Forced-air Furnaces: The What, Why, and How

Let's not get too heated, this is after an inflammable subject. Frankly it's exhausting, but we gotta do it. We gotta explain how furnaces work! And soon, we'll talk about what will replace them. I'll try to remember to put a link here when that time comes!
Links!
Technology Connextras (the second channel that stuff goes on sometimes):
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[@TechnologyConnections]

***A fascinating correction about the flame sensor!*** It turns out that fire, as in literal actual flames, acts something like a diode. This means that the furnace is able to detect flames by putting an AC voltage on the flame sensor and monitoring for a voltage drop. The fire will actually conduct some current to the chassis ground of the furnace! This also allows it to detect if a flame has gone out mid-run. Pretty neat!

[@John_Lee_]

with oil fired furnace they use something called a "cad cell eye"

[@timeimp]

You could say that the flame represents... current events. huehuehue

[@mr.monitor.]

Its called flame rectification. Fire acts just like a wire for electricity. If the fire drops off so does the path to ground = gas valve closes and furnace will attempt to re-light after a purge cycle.

[@eric4946]

Flames and even just really really hot gas has lots of ionized particles. This can be seen from the flame itself . The light produced is the result of ionized participles returning to ground state emitting light. This makes flames very conductive (vs air) and this is often exploited through conduction, capacitance you name it. Boilers usually use thermocouples on the pilot light to power a solenoid. (Which is amazing given how little power is involved) UV flame sensors are also popular and use UV light from the flame to excite a special gas to conduct electricity or some other similar technique that could be solid state or who knows there’s so many ways to do it.......

[@jrmcferren]

@@John_Lee_ Yep, since the oil flame produces a lot of visible light and the detection of the change in resistance is easy, the moved to CAD cell (which is Cadmium Sulfide also known as CdS) photo resistors. Prior to that a special thermal switch used in the exhaust (called a stack switch) was used to prove flame.

[@vect0r858]

Every time my CO monitor goes off it gives me a huge headache and makes me tired. Stupid thing!

[@MPRiley-rb6lj]

I would really like to find an inexpensive detector that would alarm not only at the unit but at multiple locations where it cannot fail to get noticed.

[@travelinghermit]

@@MPRiley-rb6lj How many stories is your residence? You should have one on every level of your home. In a single level home, the alarm is likely loud enough to wake you. CO is nefarious, and I understand you're looking for inexpensive options, but if you're a homeowner of a multi story home, I'd really recommend hardwired detectors with an integrated circuit. If your basement alarm detects CO (around 30ppm in my experience) it will send an alarm signal to all detectors on that circuit causing them all to sound in an ear-splitting cacophony that will even have your neighbors knocking on your door.

[@MPRiley-rb6lj]

@@travelinghermit Sadly hardwired is the only option I have found. Odd with everything using wireless now. You could have a gun range in the basement and fail to wake someone on the second floor.

[@alex0589]

Just rip the battery out, sleep tight

[@stevenw4549]

LOL funny that.

[@JamesPotts]

As a child, when we had a ~70% furnace, I had a lot of headaches one winter. When the furnace was replaced, we learned it was really good that our windows leaked.

[@bbuggediffy]

Jeez

[@mharris5047]

When I was a kid we had a large woodstove that was about 65% efficient. Even woodstoves are more efficient now but back then we used to go through 10-12 cords of wood every winter. Some converted these to natural gas or propane and I have seen converted woodstoves but we did not as propane cost 5-6 times as much as wood for heating. The stove was also compatible with coal but we didn't use any of that.

[@Yosef9438]

@@mharris5047 Thank goodness everyone doesn't burn wood for heat. The smoke output is way worse for all of us.

[@Bubu567]

@@Yosef9438 Modern woodfire stoves have reburners and are much cleaner than they used to be. The exhaust is white/clear(depending on moisture), though full of carbon dioxide and carbon monoxide. Less smell as well.

[@sammorris2721]

@@Bubu567 Its something that people don't know, let alone understand about modern wood stoves or heaters. Not the pellet "wood" stoves, but the ones that burn split logs. Having good insulation is key as well. Its cheap and works great for keeping a base temperature in the home as it has a decent thermal mass. Also when the power goes out you only need a small battery pack to run the blowers and they don't use a lot of power themselves. Seasoned wood that isn't rotten helps as well, it doesn't smell and works great. Electric heating works, but I would rather use the heat pump. The strain on the national grid is awful, having a Resistive load is one thing an inductive load another and a Capacitive load terrible. But that is outside of the scope of the video, Wood burning stoves / heaters are good when designed and maintained well. As we move away from bulk paper products, wood in the form of charcoal could become a decent heating commodity when soaked in a small amount of waste oil to keep the dust down and increase the BTUs. TLDR = Natural gas furnaces not bad, wood burner not awful if properly built and fueled, as well as reliable. Pure electric heating only good for small well insulated spaces with limited ventilation. Just food for thought folks.

[@Jremi95]

HVAC technician here. Your explanation and overview was great! However you missed one key safety feature, the rollout switch. This is there to stop operation if positive pressure from the blower motor is entering the heat exchanger through an existing crack. That positive pressure will prevent the draft motor from doing its job and flames will rollout of the heat exchanger. Set to trip if it detects flame!

[@dacasman]

Hearing the draft inducer kick on while you're laying in bed on a cold winter night is one of the most comforting sounds in the world man.

[@noahherritt6452]

Grew up in a small town here in Newfoundland, so using wood stoves for home heating is commonplace. Man, when you hear the blower turn on during the winter, it's the best.

[@NotThatGuy_YepThatGuy]

Where the heck is your bed in relation to your furnace?

[@dacasman]

@@NotThatGuy_YepThatGuy We have 2 furnaces in the house. One of them is on the 2nd floor where I sleep. Imagine a hall with 3 doors on one wall. It goes, my room, furnace closet, bathroom. So to answer your question, 3 feet from my bedroom. Basically on the other side of my wall.

[@KALI1080]

I have boiler heat. Hearing the pipes creak and click is oddly nice when it's cold.

[@gen2mediainc.577]

Sometimes when I sleep in the living room after watching breaking bad or something I can hear the AC spooling up on its routine

[@leonardlakey7779]

I am a retired furnace designer and you got everything right except for one thing. The flame sensor is not a thermocouple. Modern furnaces use a property called "flame rectification" to detect a flame. An alternating current is passed through the flame and the ionization of the flame acts like (a rather inefficient) diode. The control circuit board detects this small DC current. Three to ten microamps.

[@rancidcrabtree.]

Leonard is right and the nature of the sensor can be problematic when installing. People will assume polarity of your 110 vac line doesn't matter and indeed the motors and and other electrical components don't care if hot and neutral are switched. However, the flame sensor and the electronics in the control board do care and may not register a flame when there is one. I have been called to troubleshoot unit heaters on at least two occasions where this was the core issue. Alas, they were installed by electricians who should have known better, but worse argued with me about changing the wiring and insisting it wouldn't matter until I demonstrated it to be otherwise.

[@andrewt9204]

Good do know, thanks. I always have a backup on hand, but will continue to use a scotchbrite pad to clean the old one for as long as I can until it fails too often or completely.

[@lambchopsz]

Do you know why furnaces use hot surface igniters instead of spark ignition? I've had my own hot surface igniter go bad because of cracks.

[@rancidcrabtree.]

@@lambchopsz Less complicated. Spark ignition requires a high voltage source (usually incorporated into the control card) and needs to be 'gapped' and grounded properly and have a highly insulated wire just like a car's spark plug. An HSI just needs a switch on the control card capable of handling the current flow. Good to have both a spare HSI and flame sensor on hand for your furnace as they WILL fail and it will not be at a convenient time.

[@andrewt9204]

@@lambchopsz They're generally more reliable, but mostly cheaper. There's no electronics with the HSI, just a relay.

[@randy25rhoads]

Sooooo I’d like to personally thank TC. I saw this video and thought, “Huh, I never did get my furnace checked out after we bought our house two years ago.” So I looked at the furnace and saw that it was 22 years old and called someone to give it a checkup. News wasn’t good, fellas. It was dumping 12 ppm CO into our house, which I know isn’t a massive amount, but our state says the tech has to turn the furnace off for safety reasons at 6 ppm. Now my family is cold for the weekend, but we’re not dying! Thanks, TC!

[@frankrizzo7351]

Out of curiosity what state is this? Per OSHA Under 50 ppm Isn’t deadly (usually) for an 8 hour period. 6ppm-20ppm can be standard in an exhaust pipe of a furnace during operation. I know you mentioned 6ppm coming into the house though. It is a very low number considering 400ppm is usually the standard deadly level. ASHRAE, WHO and EPA call for shut down at 9-10ppm per 8 hour period.

[@allalphazerobeta8643]

@@frankrizzo7351 WHO says no more than 6 ppm for 24 hours. KEEP in mind that CarbonMonoxide is always building in the blood at certain point. That's what makes it such a silent killer, your blood is a sponge for CO, it's literally cleaning the air of CO. It takes longer for the CO to leave your blood than it does for it to enter because it bounds so tightly. This is believe is around 70ppm in the air for most people. I have friend who got slightly sick and brain damage form his furnace putting a small amount of CO into his house hold air, this was over one winter. Probably more than 6 ppm though. But parity with the outside is the goal for your household when it comes to CO. I talked to nurse about CO poisonings. He said you know those people who died from a indoor BBQ for heat had the windows open and plenty of ventilation. Yep, the small amount of CO building up in the blood is what does it. CO is not something to mess around with.

[@riccardoorlando2262]

@@frankrizzo7351 Dude said 12ppm into the house, which means his family was exposed to that 12ppm continuously. Much worse, I'd imagine, than 10ppm for 8 hours.

[@zombieregime]

@@riccardoorlando2262 especially since CO hugs the floor. If it was a single story, I can see why the cut off would be lower. Also, GET CO DETECTORS!!!!! And check your fire alarms.....

[@wheelinndealin]

Not dying is cool!

[@huntercovington9421]

As an HVACR tech I deeply appreciate this. I wish more people were knowledgeable about how we heat and cool spaces. I think HVAC is the most fascinating trade. It encompasses so many different disciplines (plumbing, electrical, high and low voltage, controls, carpentry if you install, and refrigeration) you can go so deep if you want to but most people don’t even have a basic understanding of how it works.

[@codyhufstetler643]

I did an engineering internship for a company that designed and built the internals of these things (called "heat modules". A couple extra fun facts: The burners are an interesting design in themselves. There's a small nozzle that shoots a stream of gas into a steel venturi tube, which draws air in at just the right ratio for combustion. The other end has a big hole like you'd expect, but they also have tiny channels sticking out on either side to carry the flame across all the burners during ignition. A thermocouple isn't the only way to detect flame. A very interesting method is by placing a small pointy metal rod in the flame. Because of physics and reasons, when you place a large metal surface area (like the burners) and a small metal surface area (like the pointy rod) within a flame, the flame plasma will conduct a small amount of electricity, but only in one direction. Effectively it acts like a diode and a large resistor in series. So the circuitry will check for that condition. It's actually somewhat more robust than a thermocouple - a thermocouple could get hot for some unrelated reason, but it's very unlikely that a couple pieces of metal begin acting like a diode-resistor without flame present. (Unless, of course, an intern is making a control board testing rig, and they literally put a diode and resistor across the flame sense leads.) There are also some furnaces that, along with a limit switch, have a "rollout" switch. These are thermal switches just outside the flame box that are meant to detect if flame is "rolling out" of the fire box instead of going in the tubes. This could happen in the event that the flue or one of the tubes is blocked - the pressure switch activates as expected, the flame is present as expected, but there's not actually airflow, so there's just flames rolling out into the wiring and everything. Some heat exchanger tubes have dimples, and the ones you show in the video have wrinkle bends. These help disturb ideal laminar flow and mix the gases, allowing the gases to cool uniformly. This sounds simple, but the design actually needs to be somewhat careful - any old baffle or dimple design may introduce eddy currents near the tube wall and cause overcooling and condensation, which will rust out the tube. Condensation can only happen in the final pass of a high efficiency heat exchanger - making the entire exchanger from stainless is not cost effective, so it's only that last pass that's built to withstand it. Up until that point it's exactly the same design as a standard 80%. (Also, that's the only reason why pretty much all low efficiency units are 80% - if you extract any more heat, condensation starts, and the steel tubes will rust out. You kinda covered that in the video, though.)

[@massimookissed1023]

I wonder how Destin would feel about things disturbing ideal laminar flow.

[@kindlin]

Great extra info. Enjoyed the read.

[@jamesbarca7229]

I recently had to replace the small pointy metal rod (flame sensor) in my furnace and I was wondering what the difference was between that and a thermocouple. Now I know. Interesting info, thanks for posting it.

[@marco23p]

The diode effect is because the flame is slightly ionized and thus conductive. But, in this case, the ions are flowing with the flame. Therefore, it poses less resistance to the electrons 'going with the flow' then to those going against the flow. This makes it behave like a (very bad) diode. If you apply an AC voltage to the probe, and measure the current, you can therefore measure a slightly assymmetrical current. This tells you an ionized stream of flowing gas is present: A flame! These probes can also be used for spark ignition. Useful in instant water heaters, where you want to ignite fuel immediately and not wait a couple seconds for some hot thing to warm up. You can immediately after sense the flame, no need for the probe to warm up. I think that the pointy shape is rod just to aid spark ignition, and not for the flame detection, but I may be wrong there.

[@absalomdraconis]

@@marco23p : The point will tend to concentrate the electric charge, thus leading to a higher current flow in all states, aiding both sparking _and_ sensing via the same mechanism.

[@darkreyule]

Only on this channel can you hear a technical soliloquy like "this is the anterior self regulation ignition inducer " followed by "this sparky thing."

[@williamberry4597]

And that is why we enjoy this channel so much folks!

[@krissp8712]

The hot igniting surface which becomes hot enough to do igniting was a good one too :)

[@wompastompa3692]

Anterior crocodile alligator, I drive a regulation self inducer.

[@nisserot]

Now we're getting to the burny business!

[@Elfnetdesigns]

Well all I can say here is: My old man was one of the most feared furnace fighters in Northern Indiana. In the heat of battle my father wove a tapestry of obscenities that as far as we know is still hanging in space over Lake Michigan.

[@capacitatedflux]

Oh fu - -

[@spEAMerNation]

What a beautifully written comment

[@parkerbrewer1257]

​@@spEAMerNationThis is a reference to the movie "A Christmas Story"

[@lookoutforchris]

RIP Jean Shepard

[@jconrace]

Love the Epcot/Norway guy on your t-shirt, a deep cut and excellent "technology connection" for this subject. For anybody who is curious: the face on his shirt is an oil rig worker depicted in a mural once found within the Maelstrom ride in the Norway pavilion of Disney's Epcot. In 2014 it was replaced with a Frozen themed ride. The mural depicted aspects of Scandinavian history/industry, including fossil fuel exploitation. The man on his shirt is depicted manning equipment on an oil rig. A central figure of the mural, his leonine charisma commanded the respect and awe of all who passed under his gaze.

[@paulmccoy2908]

I thought it was Chuck Norris in a hard hat.

[@HarryLovesRuth]

Maelstrom was deeply weird. Although, my husband and I enjoy following any mention of Norway with a reminder that the "Norwegians have always been drawn to the sea."

[@Sunlight91]

The most high tech space heater is a gaming pc.

[@therealdebater]

Oh yeah. A few years ago you could heat your house with one of the high-end graphics cards. I had to upgrade my PC to a 1000W power supply. I forget which card I had but it had multiple fans on it, and chucked out heat you could make toast on. The most recent graphics cards are a bit disappointing by comparison.

[@thecommenter578]

My crappy HP laptop: I'll burn your entire neighborhood

[@blakem2902]

I have found thatAn old MacBook Pro is a very good leg burner

[@kennythawsh]

Fr

[@gabrielebursi5509]

I acutally use BOINC to get my CPU to 100% so I don't have to turn on the radiator in my bedroom, it works wonders and I contribute to science too xD

[@WeirdFrog]

"Efficiency of 96%" "Correction it's 95%" How dare you betray us with this fallacy! I'll be getting my unnecessarily precise statistics elsewhere from now on, thank you very much.

[@spudnickmorty2666]

James Anouna it may be .5% less that 95 because the air filter is a little under sized, makes the blower work harder to get the amount of air it needs

[@samerm8657]

😂

[@maciejkornatowski3026]

Me, reading up on and buying heating for my house: 96? That's shit, are we still in 70s? 97+ or bust.

[@supersonictumbleweed]

It's a quarter of those 4% !

[@MayContainJoe]

The efficiency number only states how much fuel it turns into hot air. Hot air heating itself is very inefficient compared to using water as a conductor to radiate heat (usually through the floor in modern homes), but ducts are much cheaper to install than piping, which made it popular in the U.S. - the land of "cheap" energy. There is a KZbin channel of a disabled guy struggling with paying his propane bill every year, while elsewhere even poor people living north the 50. latitude manage to keep at least one room warm on a moderate rate (like $30 per month) using radiators fed by a gas powered furnace. The problem starts with the concept of heating just the one room you're in doesn't even exist with central forced air.

[@bw1235]

One more safety feature- the access panel interlock switch, which you likely defeated to get your interior shots.

[@iyrsh07]

it's not *essential* since you're unlikely to leave furnace open,but I can see the danger.

[@theannoyedmrfloyd3998]

I'm reminded of the time we switched the propane tank on my grandparents' furnace. The fuel pressure was higher than the previous tank which meant while there was combustion going on, excess fuel also got pumped into the furnace and was unable to exhaust fast enough. I woke up with headaches for an entire week (my room was in the basement) until I figured out how to adjust the fuel pressure. If I hadn't learned that, my grandparents' house could have exploded or worse. Which is why furnaces need a fuel pressure regulator. Why my mom and I were at my grandparents' house is beyond the scope of this comment.

[@drogenmuellerable]

what's worse than a exploded house?

[@connorbernier7689]

​@@drogenmuellerable the former residents dying...

[@Kudlaty771]

flatly I can already tell why and without getting into detail, I am sorry. Someone young shouldnt have to learn how to adjust a gas valve because of circumstance. cheers to not being at that point in time anymore.

[@deborah8887]

Sounds like an interesting backstory we’d like to hear…

[@letsnotplaywithelectricity9346]

Been a service tech for 16 years now, and I have to say this is the best explanation video about modern furnaces that I've seen on KZbin.

[@wendyokoopa7048]

I'm laughing at your screen name and I shouldn't. Can I go cuddle a creature that has the ability to store 10 thousand volts in his tiny yellow adorable body?

[@squishmastah4682]

@@wendyokoopa7048 Lemme check my Magic 8 Ball...

[@georgf9279]

@@wendyokoopa7048 You want to paint your cat yellow?

[@GloryofLlama]

TFW it's Saturday afternoon, your friends are all married with kids, you're in a robe drinking chocolate milk, and you're watching a video called How Furnaces Work.

[@alex0589]

Shivan so you really dodged a bullet then, uh?

[@ncot_tech]

Or it’s Sunday morning and you’re sat in bed watching it on an iPad, contemplating going downstairs to use your gas burny cooker to make bacon. While you know your friends have been up since 7am trying to herd their children.

[@RandallJennings]

I watched this while setting up a fort for my two kids. Win win.

[@GloryofLlama]

Haha yeah, really this TFW was kind of ambiguous, like half of me was in existential horror, and the other half was elated by the freedom to just chill and watch random technology videos without any responsibility or need for appropriate clothing

[@27dcx]

they sell "condensate neutralizers" which is literally a plastic box with a couple chambers full of limestone chips.

[@Velcr0man652]

First this channel helps me troubleshoot my dishwasher and consistently get clean dishes out of it and now it tells me how my furnace works which just so happens to be having issues right now, love the content keep it up!

[@TheJJluv123]

I've never been so excited anticipating a future video about heat pumps.

[@tayzonday]

This guy is like my Dad explaining things when I was a child. But I’m almost 40.

[@asmodeusz28]

My own dad explained things a bit more like the father from Calvin & Hobbes. It was fun, but I rather like Alec's style.

[@remlezar4439]

He has such a way with explaining things to make sense. He does make you feel like a child listening but after the video you feel smarter and then the jazz plays!

[@Lozoot2]

Holy shit, not only are you Tay Zonday but you're almost 40??

[@YouTubestopsharingmyrealname]

Are you the actual TayZonday? Of Chocolate Rain fame? The internet has taught me to expect impersonators...

[@Lozoot2]

@@KZbinstopsharingmyrealname It literally takes one click to check his channel

[@accidentalmeme5327]

You know, I was half expecting him to say "through the magic of buying another one" somewhere in the video.

[@PaulMansfield]

there should be a cross-over with the lock picking lawyer memes, "through the magic of buying another one of the things Bosnian Bill and I made"

[@Kihidokid]

Through the magic of already having two of them

[@Alex_1A]

16:29 He does have 2! Or at least had 2.

[@aterfelis4708]

How many furnaces does one house need?

[@Furious321]

@@PaulMansfield "Let's get this heat exchanger out onto a tray..."

[@John_NJDM]

This is one of the smartest and most informative channels on KZbin. I spent some time as an engineer in the Coast Guard, and I enjoy learning about technical systems of all kinds. This, and many others, were great videos!

[@chonasassl2558]

Masterpiece of a Technology Connections video.

[@nefariousyawn]

I love how nonchalant or deadpan he is when delivering his puns.

[@glenncaughey5044]

Takes a lof of takes to do that 😁

[@CreamAle]

The true way puns should be delivered.

[@wendyokoopa7048]

He's very very newhart esque

[@nickjanssens1045]

I lost my shit when in the retroreflector video when he said something like, "These retroreflectors are called cat's eyes because they work like the eyes of a cat. Let's take a look at one." And then he puts a cat on the table. Comedy gold.

[@jonathanespinoza94]

I loved his U Tube pun

[@travelinghermit]

I have been servicing both 80 and 90 plus efficiency furnaces for 3 years in chilly North Dakota. I have worked with 4 local contractors and a myriad of technicians. NOT A SINGLE ONE has been able to describe some of the design features of these furnaces. You have slain ignorance in as much time as it takes me to service the average call! Thank you for helping me help others!

[@astranger448]

Forever problem with technology and especially teaching. Staying up to date requires effort that not everybody is willing or able to put in. It results in kids leaving school with outdated stuff and technicians sticking to what they learned ages ago.

[@J-1410]

Must be a real ND person. I lived through the oil boom and all I heard was "cold" "freezing" "the opposite of hell" "frozen wasteland" and "forsaken ice box" My guess is eastern ND as western is alot of electric heat.

[@travelinghermit]

@@J-1410 I'm a technician servicing Minot AFB. All our furnaces run natural gas. The base keeps an emergency store of propane for SHTF situations. Once a quarter, they run propane through the lines which runs too rich for all the furnaces, power vents, etc. That means soot builds up on the flame sensors often (most common cause of furnace calls for us). As far as what I feel about ND winters? I came from New Mexico, Turkey before that, and California before that. I do not dig the winter here lol

[@J-1410]

@@travelinghermit what's their logic for running propane? Make sure it works?

[@travelinghermit]

@@J-1410 If you mean why store propane as opposed to gas, I can't say. I can say I've never seen natural gas under any kind of long term storage like I have with propane. I don't actually know if storage would be a consideration.

[@LloydLynx]

It's quite spectacular when the heat exchanger of an old furnace goes. The pressure from the large blower pushes the flames back out and flames come shooting out the front of the furnace, which then trips all sorts of safety features and shuts it down. There's sometimes a loud bang when it happens. It's more common than you'd think.

[@Deacetis1991]

This year, I've replaced more gas forced air systems with Geo and air to air heat pumps than ever. I'm doing two 20+ seer variable systems just this week. Even with slightly higher costs on electricity in some places, the overall efficiency is so much higher, like an energy advantage of 3 to 1.

[@redacted2871]

As a Frenchman that sometimes struggles with spoken English ; thank you so much for the subtitles !

[@FatterPidgeon]

This channel is the closest I will ever get to a having a degree in something.

[@megazenn22]

you can get a few more degrees if you get one of these :)

[@WespectRamen]

@@megazenn22 lol

[@rorysparshott4223]

I hope that degree is in celcius for the sake of sanity

[@TRunner96]

I thought a degree was required to watch this channel

[@mcspikesky]

But he never pointed at the things and said which was which :(

[@ofoosy]

I lived in an old home that relied on wood fires for heating. Two for the whole house. I live in the inland northwest and our temps in the winter bottom out at around 10°F with occasional dips into the negatives. Our family converted the fireplaces to natural gas with some odd retrofitting. This video makes me want to really investigate how efficient they are! they've been around for twenty-two years now. When I was a young child I remember being fascinated at having to heat my home with a 19th century wood stove. Thanks to your video on heat pumps my family's home has had a heat pump installed as an addition. And now those gas fireplaces run much less often. And now we have solar panels on them for a completely anachronistic looking home. One look back and our eyes on the future. Love these videos. Thanks for making them!

[@capacitatedflux]

When you interjected with the "this is a correction" I, admittedly foolishly, expected you to say something like "I misinterpreted the number" or "I suggested a thing that was a positive is actually a negative!" but it was a simple change of 96 to 95 (which is still an A!). That's dedication to truth right there, even if it wasn't necessary or even really disputable, and it is to be commended. (I say "admittedly foolishly" because if it was actually misinformation it would never have made it into the video in the first place, thanks to your keen editing and the production value of these videos.)

[@TheDigileet]

They're also used in semi trucks, and they just use the same diesel as the engine. It can keep my truck as hot as 85°F (29.4°C) for an entire night when it's below freezing outside, and it uses a small fraction of the fuel it would take to run the engine all night.

[@Hansengineering]

That is fucking cool.

[@Corrodias]

Ooh, neat.

[@bassam_salim]

29.4 is hotter than most people see as comfortable temp, these days the temp in my house is 29-31 and I run the ac to cool it down, 25-26 is what I say comfartable for sleeping

[@TheNiteNinja19]

Yeah I remember the one that was in my Peterbilt, darn thing could roast you out in the middle of Minnesota. All it uses for power is the 12v DC from the battery to power the fan and the ignitor. Once lit, it burns efficiently like a kerosene lamp (essentially the same fuel).

[@cedricpomerleau5586]

Bassam salim I can barely sleep over 23. I heat my place to 22 during winter, 18-19 in my living room.

[@birbo5603]

People take these for granted, but they're actually really interesting pieces of technology.

[@umangmalik]

that's basically the theme of this channel

[@Mdudeman13]

These topics are my favorite, I hope he continues to make more.

[@tech99070]

Furnaces are comprehensible pieces of tech which makes them really cool to learn about

[@kaitlyn__L]

what I find really interesting is how similar it is to a huge fan space heater. you just have heat from burning in the giant heatpipes, instead of resistive heaters stuck to heatsinks. Both provide instant, forced-air heat. Hydronic (radiator) heating works more like those oil-filled electric heaters... takes ages to get going and then overshoots the temp after the thermostat gets triggered. I have to constantly twiddle the thermostat to effectively reduce its tolerance from ±0.5°C to ±0.25°C (but with the overshoot, it takes the actual room temp range from ±1°C to ±0.5°C).

[@PhazonBlaxor]

I found it very interesting because I've never seen a gas furnace before (never seen any household stuff functioning on gas really). Wouldn't have thought that something so simple sounding could actually be so complex.

[@benjamino5]

As a new home owner who's had some real furnace repair and replacement headaches, this video was wonderful in helping me understand what I'm paying for and why my old furnace had to be replaced.

[@ravit50]

Love hearing the little fan then the snapping of the ignition system, the woosh off fuel. Lovely things. Thanks Armstrong air

[@ChetCoenen]

Our water heater exhausts became clogged when I was in highschool. There was about a week where everyone in the house felt like death. Finally, when my dad almost didn’t wake up in the morning we had someone come out and check our systems. The HVAC guy brought a sensor in and literally exclaimed upon going downstairs “you all should be dead”, and opened every window he could find before even starting to fix the issue.

[@matthewmiller6068]

Yep, dangerous stuff -- always good to have multiple CO & Gas alarms if you have or use any fuel powered appliances...or even have an attached garage (some have died from push-button-start cars that were accidentally left running in connected garages). We always had 1 on each main floor (basement 20ft from furnace, livingroom 20ft from fireplace, upstairs central to bedrooms) plus an additional one in the room above the garage. I also like to have one indoors where any extension cords come thru windows/doors while running portable emergency generators.

[@TheDonSapius]

Y'all got super lucky, that's scary AF.

[@nthgth]

@@matthewmiller6068 like I needed another reason to hate pushbutton start...

[@westcheap]

"and what lives on the other side of those tubes are the flamethrowers." t h e w h a t

[@gregmercil3968]

Technically called “inshot” burners.

[@willpower3544]

did anyone notice he said "flamefrowers"?

[@ryank1273]

@@gregmercil3968 Flamethrowers sounds way better.

[@ZenoDLC]

Flamethrowers, it throws flames at whatever you point it at

[@gregmercil3968]

@@ryank1273 lately, I’ve been calling them “thrusters.” 😆

[@Naruedyoh]

Hey, thanks to this video I was able to identify the problem with my water heater and saves like a hundred euros calling a technician for a furnace no longer in production and with the manufacturer out of business

[@guyfriendo2917]

So glad I found this channel, it's very informative! And interesting enough to binge watch

[@caryrodda]

"But I digress..." I think most of us like your digressions!

[@IanDunbar1]

"Fun" story. At one of my previous jobs we were all given low level carbon monoxide poisoning. According to our maintenance guy, the heat exchangers had cracks big enough you could slip your hand into them. A "lack of funds" meant that they system hadn't been inspected in quite some time. When the carbon monoxide alarms went off, one of our managers told people to get back to work and that it was a "false alarm". Yeah, no. Pretty much everyone ignored him, thankfully, and evacuated. When the fire department arrived we were told it wasn't safe to be in the building.

[@regular-joe]

But I vengefully want to know what happened to that manager (and company)!!!

[@IanDunbar1]

@@regular-joe You'll be surprised (or maybe not) to learn that absolutely nothing happened to him, and as far as I know he's still there to this day. He was upper management (number 3 in the company basically), so there wasn't much that was going to happen realistically. I suspect COVID has put a MASSIVE damper on their sales though. I can't imagine they're doing well these days.

[@stevethepocket]

@@IanDunbar1 Ideally he should have been arrested for what he did. Was it a company so big that they effectively owned the police, Capone style?

[@megafarad4933]

It doesn't really require much funds to check for cracked heat exchangers. I've been doing HVAC, plumbing, and electrical for years. It always seems heat exchangers get people confused. If there is a crack in a tube, the blower will blow air through it. An idiot can stick a grill lighter in a tube and turn the fan on. If the flame persists there is no crack. If the flame dies there is a crack.

[@IanDunbar1]

@@megafarad4933 Dunno, that was just the story we were given. That said, I'd believe it. They were crazy penny pinchers. For instance, the owner used to refuse to use curb side check-in at the airport because you were expected to tip, and he felt like that was an exorbitant expense.

[@John-hc8fy]

30 years in hvac I don't no why I like this video it's good stuff

[@BiznatchWang]

I can't wait for your video on heat pumps and their challenges! As someone who lives in a municipality that is banning furnaces from new construction I'm very interested in knowing the tradeoffs of that heating system.

[@halfSpinDoctor]

Our furnace just broke, so I suddenly dived into a deep hole of "how furnaces work". This video is very timely.

[@Jusiun]

How did you survive the winter?

[@halfSpinDoctor]

​@@Jusiun by getting it replaced ...

[@bbuggediffy]

@@Jusiun Portable heaters

[@mtldax]

Re: negative air pressure Modern homes actually have some thing called a HRV or ERV, they recover energy while ventilating the house which allows the house to be very well sealed. This might be a neat video topic for you ;)

[@alexanderbresnahan2932]

Yeah, these things are slick! They pull fresh air from outside and push air from inside out, but through a heat exchanger to take the ~70F air from inside your house and reclaim some of that heat by warming the -30F degree air from outside first.

[@ShadowZero27]

my windows are older than i am so i do not have to worry about this

[@103213able]

Yes please can you do a video on this?! I have one and I have no idea how it works!

[@travelinghermit]

I hadn't heard of these! They sound nifty!

[@thepurdychannel8866]

What heat pumps?

[@jyesucevitz]

I've been in wholesale hvac sales and tech for 35yrs. since I was 19. specifically gas fired furnaces. I live near Boston, MA. you nailed this video perfectly. outstanding.

[@yomanleavemealone9815]

Any idea how to make one of these things quieter?

[@EvilishDem0nic8732WhatItDo]

Techmoan brought me here but I'm already subscribed so expect traffic today bro

[@DaddyBeanDaddyBean]

I have a condensing boiler in a hot-water-baseboard system. When the HVAC company put it in, they routed the condensate through vinyl tubing into my sump pit. A few months later I found a trickle of water running from under the boiler. They had connected the condensate drain to the vinyl tubing by inserting the ends of a little piece of 1/2" copper pipe; the condensate had eaten through it. It probably wasn't doing my sump pump any good either. (Normally zero groundwater entering the sump.) I replaced the copper piece with PVC, and made a big "U" of 3" PVC in the sump pit, one side an inch lower than the other, filled to the top with marble chips; the condensate drips into the high side, so the water has to pass through several feet of marble before it can escape out the low side. Copper pipe fittings nestled in the rocks on each side for a year showed significant corrosion on the inlet side, and none at all on the outlet side; five years later, the condensate had dissolved about 3" of marble from the inlet side, while the outlet was still full & clean. Seems like it's working. 😁

[@Corrodias]

That corrosive water is no joke. I've had a tech warn me that I need to make sure drain water from this stuff goes directly into the nearby drain and doesn't drop onto the concrete floor, because it'll damage the concrete.

[@DaddyBeanDaddyBean]

@@Corrodias having seen firsthand what it does to marble over time, I don't doubt it.

[@TheDonSapius]

That's genius and kinda scary.

[@BY-bj6ic]

@@DaddyBeanDaddyBean Well marble is metamorphized limestone. You can bake marble to make lime

[@spencerwilton5831]

DaddyBeanDaddyBean The marble chip method is actually an approved way of disposing of condensate in the UK building regulations. Ordinarily, condensate is routed to a drain where it is diluted by other waste water. It is however acceptable if there is no suitable drain to connect to a soakaway located a suitable distance from the wall / foundation and backfilled with limestone.

[@michaelimbesi2314]

Another thing to note regarding carbon monoxide: it’s likely part of why they use induced draft rather than forced draft fans. Having the blower before the tubes would put them at slightly higher pressure than the ambient air pressure, which would mean that any leak in the tubes would expel combustion products into the house’s air supply. With induced draft, the tubes are at a lower pressure relative to ambient air, meaning that a leak there will suck clean air into the tubes and won’t let CO into the ventilation system. Of course, any leak in the PVC exhaust will still contaminate the interior, but there’s less risk since it isn’t subject to the same intense thermal cycling as the fire tubes.

[@audvidgeek]

oil furnaces do just that...forced draft. The oil burner pushes air into the combustion chamber, as high pressure oil is sprayed into it with an atomizer nozzle. A spark electrode ignites it the air/fuel mixture.

[@Stoney3K]

That's the reason why water boilers do use forced draft, because there's no risk of CO leaking into the domestic air vents. Some even have turbines to recover even more latent energy than just forcing air through, turning them into small-scale turbojet engines.

[@johnparham7112]

better that than be dead! Me, an intellectual,: “Hmmmm”

[@thenasadude6878]

Also placing the fan after the tubes lengthens its service life and makes it cheaper to produce, because less thermal stress will occur

[@jhonsiders6077]

After seeing this I got rid of the ventless unit ! replaced it with a vented unit .

[@jamesknix]

New homeowner with one of these that’s currently on the fritz. What a fantastic video! Crash course in my own furnace system! Would have liked to see a note about condensate pumps as well! We’ve reused this water vapor, but now we have water in the house that we have to get rid of!

[@tacos5631]

My old furnace that was built in the 80s still has a gas pilot light that you have to light to fire the main burners. And it has a pretty interesting limit switch, it spins! It's basically a giant heat sensitive probe stuck in the exhaust chute, when the main burners are lit, the heat from them extends a big ol thermal bimetallic strip and causes it to extend to a certain point. When it extends all the way, it kills contact to the blower motor.

[@rowal23]

Me: Lives in the cold north and knows full well how furnaces work Also me: watches the entire video anyways and enjoys it

[@stevenpotter8228]

same bro

[@alanhilder1883]

Me: In Australia, the reverse works fine here.

[@abjz71]

Thats ok I'm a licensed hvac tradesmen and I sat here and watched it

[@MarkMcKinney94]

I worked for an HVAC company for 4 years and still watched to the end.

[@AutistCat]

This is quite fascinating to me because I’m from Iceland and our heating is usually done with hot water, piped into homes from geothermal power plants. It’s a really interesting system, I wonder if you might cover that subject some day! ❤️

[@donnawander7710]

Tom Scott did a video on that semi-recently.

[@AutistCat]

Donna Wander Yes, I loved it! He did a series of videos here and they are fantastic, no silly misinformation or nonsense like is so often the case with content about Iceland. Tom Scott is great.

[@Karjis]

If he makes short series (5 part? :D) about ground source heat and heat pumps he might mention areas with lots of heat near the surface like Iceland and if I am not completely wrong areas near Yellowstone also. I mean that some places you don’t need heat pump to get hot water, just a pump.

[@tankermottind]

Living atop a supervolcano does have its advantages.

[@NicholasLittlejohn]

@@Karjis Geysers, CA too

[@jelleluiken]

As a Dutch service engineer I work on these systems daily. Altough we have some slight differences, you have explained it very very well. Thank you! Awesome to see something in my industry :) Adressing to the change of heating systems to heat pumps due to climate change, our heaters in the Netherlands are already ready for hydrogen. It’s as simple as changing the gas valve (if they use the gaslines used for natural gas. If your interested in these type changes they are working on, please let me know. I can help you get in touch with manufacturer.

[@johnhammond6248]

I just started HVACR School and this video is very good and insightful, and is helping me understand more about my future career! Thanks for another great video :)

[@flyingninja1234]

"I'm really in the middle of nowhere." Rural folks with giant propane tanks, can confirm.

[@xaenon]

I'd rather live in the middle of nowhere with the giant propane tank, to be honest. Granted, it's probably not as 'convenient' as suburban life, but I'll wager it's a lot more peaceful.

[@Slippergypsy]

i live 25km outside of sydneys CBD and i have 2 30kg natural gas cylinders on the side of my house for the stove and bbq and heat my water with the power of the sun

[@xaenon]

@@Slippergypsy Sounds like a righteous setup, friend.

[@Ilander86]

@@Slippergypsy In America, 500 gallon tanks are relatively common for residences! Around 770 kg!

[@flyingninja1234]

@@xaenon Agreed.

[@willpreston6881]

I definitely exhaled harder than usual at "you might call them U-tubes."

[@postitman]

"exhausting job" is what did it for me, haha...

[@allmycircuits8850]

I saw it coming when he said about series of tubes!

[@andrewxc1335]

I know, it was like one right after the other for a good minute, there.

[@flyingjunkie1235]

I just got this exact furnace 2 days ago, so it was nice seeing the stages explained on the same one I have.

[@jeffreymiller1822]

Thank you for making these videos. I watched it when it came out last year and my furnace went out this morning and thanks to your video I felt confident enough to fix it myself. Ended up changing the igniter and gas valve!

[@davemi00]

I’ll call a Service Tech and get the Parts and Replace them myself. If it’s practical.

[@EmilFr]

It's so nice living in Iceland, where we get geothermal water out of the ground to heat our houses, provide hot water from faucets and even to heat up driveways and sidewalks when it's below freezing... and it's dirt cheap.... actually, so is our electricity, since that is either hydro or geothermal too

[@Adam-qs5ir]

My natural gas costs me no more than 75 us dollars (or 10,429 Krona) a month throughout the winter. What does geothermal heating cost? Just curious.

[@Jupiter__001_]

@@Adam-qs5ir Geothermal heating only costs as much as the installation and maintenance of the heat pump, but its effectiveness varies from location to location. Recall that Iceland is highly volcanic, and hence there is a very good return on investment with a geothermal heating system. The issue is that in most places, one must dig a long way into the ground (at least 100ft, the deeper the better), so as to escape the variable temperature of the upper layers. This may be different in Iceland.

[@Adam-qs5ir]

@@Jupiter__001_ makes sense, drilling that deep probably costs a fair amount.

[@Jupiter__001_]

@@Adam-qs5ir Plus there is the small cost of driving a pump to move the water (though a heat exchanger can also be used, there isn't much point in Iceland).

[@Adam-qs5ir]

@Mark Kennedy that's hard work, but I'd enjoy it

[@Dr__Money]

Oh man when he said "a series of tubes" I had a war flashback

[@fffUUUUUU]

It's okay mate. They are all dead by now

[@rpavlik1]

Got a new furnace a few years ago. It came in a big truck. They just dumped my old one on it.

[@TEHSTONEDPUMPKIN]

Its not a big truck

[@RichieRouge206]

Forced warm air systems were popular here in the UK in the 60s and 70s but they were renowned for failings and setting fire to rooms/houses. Everything is mainly gas fired central heating here now - a central boiler heats radiators or under floor heating in homes. Another excellent video dude

[@gregakinson2800]

You always have great and informative videos with a splash of humor........thank you so much!

[@firemanjoe9491]

As a firefighter we get called on so many smoke/fire investigations for residential structures that utilize these devices to heat their home. As shown in this video they are wonderfully crafted and designed in order to not be the very reason your home burns down but they can only do so much. Save the money needed to maintain and repair these routinely. The cost of an HVAC appointment is pennies on the millions in comparison to the potential loss of life suffered from lazy or forgotten responsibilities. Be safe and that you for your awesome videos my man! Your are a treasure!

[@tech99070]

I have literally never heard of a forced air gas furnace causing a house fire, how would that even happen? They're metal boxes with a regulated gas supply. As he said about 20 times the biggest risk by far is releasing exhaust into the house, which is also very rare. Their most common risk is failing to work due to open circuit from the safety devices. They aren't going to cause a house fire.

[@Coconut-219]

You forget that at the end of the day all of these safety features are still being built by the lowest bidders.

[@Skyhawk1998]

@@tech99070 A bad rollout or gas leak could lead to a larger fire.

[@m8onethousand]

@@tech99070 I'm not a firefighter nor an HVAC guy, but if I had to wager I'd say electrical stuff, bypassed sensors, or bad gas pipes/valves. I've personally seen more than a handful of really disgusting and thick aluminium to copper connections that just send shivers down my spine, as well as bypassed sensors. Not so much about gas pipes other than solid copper ones which are "okay" I guess, since their usability depend entirely on the type of natural gas you get so as to not form flakes of whatever chemical stuff it is that happens with copper pipes and certain types of natural gas.

[@FishFind3000]

My grandfather has a boiler for radiator heat. He had no ac until about 5 or so years ago. Living in Chicago.... will all those 110°+ heat waves. Being 80+ years old. With a heart condition. Life finds a way!

[@absalomdraconis]

I'm curious when someone will come up with a two-way radiator system based on heat pipes. Seems like a vacuum-pressure system should be somehow workable.

[@lutyanoalves444]

@@absalomdraconis you mean an air conditioner pointing outwards? heheheheh i think it would be very expensive to run compared to gas, or am i missing something?

[@bekindandrewind1422]

Thank you for the outtakes... I needed to smile today.

[@vickireynolds4055]

I love your channel! I watch it even though I don't understand a large percentage of what you say! I usually learn something, so that's progress!!😂👍👵

[@ZGryphon]

Data point: In the northern half of Maine where I live, we don't have a natural gas pipeline network, so most of us are burning No. 2 fuel oil delivered by truck, either in forced air systems or, as in my 100-year-old house, boiler-radiator systems. A few avant-garde types (like my father) are using propane out of cylinders instead, like you, and of course there are the holdouts who still burn wood, and those pellet stove wackos, but fuel oil is still by far the most common choice in these parts. Hot water systems are still pretty common as well, although that's at least partly because central air is pretty uncommon in private homes. It's only hot enough to need AC for about six weeks a year, anyway.

[@PCPSolutions]

I am one of those pellet stove wackos. It's my primary heat source with a heat pump system as a supplement. I live in Northeastern PA, so not exactly warm. I wouldn't go back. Pellet stoves are efficient and cost effective. (I'm only a convert within the past 3 years, from an oil fired boiler) I will never go back!

[@Asmodai1234]

Here in Nova Scotia, truck-delivered fuel oil is the predominant fuel source as well. I'm glad I have electric + heat pumps since it means I don't have to worry about tank condition or CO.

[@jrmcferren]

@@PCPSolutions You are close to the Anthracite deposits, converting to coal (Anthracite) is going to be cleaner burning and less expensive, but not so renewable.

[@petersilva037]

I'm in Quebec, which is kind of Saudi Arabia for electricity... the default/cheaper way houses are built is to use resistive baseboards here. The only reason this is done is because the equipment is cheaper to buy and install. I have one of those 100 year old houses with hot water radiators. Replaced the fuel oil burner with an electric boiler a couple of years ago. It's comfortable, but need a completely separate system for cooling, and there is no air exchange.

[@IrisGalaxis]

I have a wood stove at home... It's the cheapest variant and it makes no sence to have central heating for a house this small. It is probalby the most common method here. Other folks round here normally have boilers with radiators if the house is on the older side, all fueld by oil bought at the gas station, or, if the house is newer, they heat themselves via AC if they have enough money to pay that electric bill

[@cho4d]

technology connections: "but it has a bit of an exhausting job ahead of its self" me: * raises eyebrow * technology connections: "... exhausting!" me: * eyes closed smh *

[@over00lordunknown12]

This video isn’t like candy for your channel! All the separate components working together to ensure safe and constant operation really works perfectly for the purpose of this channel (how technology connects together).

[@JuanGerardoHernandez]

Your channel is pure gold!!!

[@theGhostWolfe]

I live for the “[adjective]ly smooth jazz line” at the end of each episode.

[@chrismanuel9768]

Orange. Metallic. Hairy. Loquacious. Moist. Greasy. Speckled. Bright.

[@0oShwavyo0]

Adverb tho?

[@theGhostWolfe]

@@0oShwavyo0 I guess. I moved schools a few times as a kid, and I distinctly remember getting to the part of my education where we started on nouns and verbs, changing school, and the new school had apparently already done that, and I never really got a good grasp on grammar, and I mostly manage well enough to not swallow my pride and go back to cover that >.>

[@theGhostWolfe]

@First name Last name ??? I feel like a lot of army brats switch schools as kids. I’m not bragging that I somehow failed to learn some of the most basic shit kids know, I’m complaining about it.

[@douwebdevries]

@@theGhostWolfe It is never too late to learn :)

[@Yelawolf269]

Most furnaces: has all these fancy safety features and lockouts to stop it from working with the covers off My 1978 Lennox furnace: you can operate me with the covers off but don't stick your fingers in here 😂

[@teacfan1080]

About a decade ago, my parent's furnace in their home, which was a few years old, developed a crack in the heat exchanger as you mentioned. The furnace shut itself down automatically. Of course, this happened during a frigid cold snap in mid-December when lows reached the -20's F and highs barely reached zero. They had a Tempstar furnace. Tempstar overnighted a replacement heat exchanger to them but it was for a different model furnace!! All in all, it took a week before their furnace was back running normal again. Until then, they used four different space heaters to heat the home during the dark hours. One was one of those oil filled radiators which they blew a fan through to help heat the area. During the day, they opened all southern curtains of the home to allow the sun to heat the home. Thankfully, it was sunny most of the time. Never once did they go under 60 degrees in the house. A spokesperson for Tempstar was appalled by their parts delivery saying "These people should NOT have needed to wait a week in frigid conditions for a part for their furnace!"

[@reeceguisse17]

I have only recently (summer 2021) found your channel, but the crossover between How It's Made and Connections (with James Burke) have me hooked

[@vBrolin]

"Heat pumps... They are indubitably the future of home space heating" Living in a house that have had geothermal heat pumps heating it since 1982, I just gotta say welcome into the future whenever you are ready :)

[@absalomdraconis]

The best installations range from inconvenient to impossible to install after the house is built, so not so suitable to suburban & urban locations.

[@vBrolin]

Jared Maddox yeah its far easier to convert if you are heating with water instead of air. Then it's just a two day job.

[@Lawrence330]

@@absalomdraconis If you already have central air, you can have a heat pump. The air handler replaces your existing furnace and the refrigerant lines are run just like a typical A/C installation.

[@absalomdraconis]

@@Lawrence330 : The best systems are geothermal. Unless you have a reasonable amount of easement-free land, you can't realistically install them after the house is built, only before.

[@Lawrence330]

@@absalomdraconis The best heat pumps you mean. Gotcha. I mistook your statement to mean that you couldn't easily switch to a heat pump (not specifically GT) after the house was built. Even an air source heat pump is quite efficient in the lower half of the U.S. I'm in coastal VA and have had a heat pump here for a decade. This house is very poorly insulated and ventilated, so I imagine newer/better construction would see a bigger benefit than I do.

[@TheVirtualTim]

I had a furnace fail to light (and why does this always happen on a weekend?). It would light, then shutdown within a few seconds. The repair tech asked if I was handy with basic tools (I am), had me open the furnace, remove the thermocouple, and confirm it was mostly black (it was) -- then told me to grab a wire brush and brush off the carbon buildup (I used a Dremel tool) until it looked completely clean/new again. I put it back in and the furnace worked perfectly. The advice he gave me was that ... even before you have a problem with your furnace, buy a spare thermocouple and a spare inducer fan for your furnace because these were the two most likely parts that can fail and leave you without heat. Having them on-hand means you can just swap out the parts and have heat again without making a service call in the middle of the night or on a weekend.

[@abjz71]

There is no reason to buy a spare inducer motor as they rarely just fail and there is no reason to buy a new flame sensor as they can almost always be cleaned. Now a new furnace ignitor that is a whole bother conversation. Buy an extra one actually buy two because you are likely to break the first one while installing it

[@dshipley]

The first failure on my 9 year old furnace was the draft inducer (happened earlier this week). I also had a nice crack in the plastic duct behind it and replaced that as well.

[@SETX_Sirens_and_Rail_02]

Coming from someone going to school for this field, I will say that this video was very well put together. Also, here in the south (especially in south Texas) we only ever install the 80% furnaces and just completely avoid the 90+ units simply because we don't have much of a need for higher efficiency heating since it rarely gets very cold. Whenever it does get very cold, it is very short lived which really beats the purpose.

[@m2heavyindustries378]

RIP this comment after the Texas Power outage and resulting winter catastrophe

[@superman60201]

Great video, thanks for tackling what many of us have in our homes and know not much about!

[@ReyMysterioX]

Finally I understand why Airbnb is so persistent about telling me if a carbon monoxide alarm is present in the flat / house.

[@NicholasLittlejohn]

Liability for them

[@4R8YnTH3CH33F]

@@NicholasLittlejohn not dying is also a neat side effect of this corporate policy

[@3rdalbum]

It doesn't make so much sense in properties that are heated solely by air conditioning!

[@ReyMysterioX]

@@NicholasLittlejohn I was a little bit a wonder why this was so important to Airbnb. They specifically highlight if no CO alarm is present. It's a little bit unusual because in Europe, where I live, hot water radiators are the most common heating system. That's why I found it unusual to make such a fuzz about the CO alarms. But now I know why.

[@SupaDanteX]

Alec's own pinned comment: "Turns out the fire can be a diode!" At least two comments I've read so far posted after: "Actually, the flame can be a diode."

[@SupaDanteX]

In honour of those people, Alec I have to add my own 2 coins. You may not know this, but if done correctly, fire can actually work like a diode. And so you don't need a thermocouple. It's crazy, I know.

[@grn1]

I'm going to assume they either watched and commented before he got the correction up or were watching on mobile or something and just didn't see it. I pretty much always watch on PC, the few times I have used mobile (and looked at the comments) it felt incredibly clunky and I could easily see someone missing a pinned comment.

[@SupaDanteX]

@@grn1 I would assume they just missed it. I know that happens. I was just trying to make a joke about it :D But yea Alec's comment was at least earlier than all other people's I saw. At least if the time stamp on the comments is to be believed.

[@dickcheney6]

A diode can also create a flame with enough current. Well, once, anyway.

[@hewhohasnoidentity4377]

@@mojad6137 You can actually breathe water indefinitely, up until you first breathe air. Research is being done to find a way to allow us to return to filling the lungs with liquid for health purposes and for deep diving or space environments.

[@tzisorey]

"The Heat Exchanger is a series of tubes" A thermal Internet?

[@ktm42080]

I just bought a house, two years ago, and it had a neglected oil boiler. I got it up and running for the first season but only used it for backup heat. I installed an electric water heater and a pellet stove. Pellet stoves have all the same safety devices as a furnace, pretty neat actually. I tore out the boiler and installed electric baseboard heaters, its a small house, for primary heat but usually rely on the pellet stove. Great video!

[@ACBMemphis]

I had my furnace replaced this year, after the old one wouldn't start due to a cracked heat exchanger - one of the sensors stopped it. The repairman told me a story about family who had a leaky roof and put a blue tarp over the leak - and also unfortunately over their heating vent! After they started getting very sick, they realized what was happening before it was too late. And after hearing this story, I went out and purchased a carbon monoxide detector to go with the new furnace! Thanks for the very educational video...

[@liesdamnlies3372]

@ebulating The combustion is always going to produce some amount of CO though. You really need that sensor to be in the living space, away from the flame. Then, if it's going off, you know you have an actual hazard.

[@nulious]

I'm living in blue roof territory (sw Louisiana) right now and I'm seeing a lot of houses that have their vents covered...

[@uzlonewolf]

@@liesdamnlies3372 Putting it in the return air duct would take care of that. If you have so much CO in the air going to/from your living space that it's tripping a CO alarm (which actually requires quite a lot of CO to trip) then you have way more CO than is safe.

[@liesdamnlies3372]

@@uzlonewolf Fair point.

[@collinpearsall9084]

The flame sensor, as far as I know, actually works by conducting electricity through the flame, not by sensing a chance in temperature as stated at 15:53.

[@schellenbergenator]

Yes and no. In a high efficient condensing furnace you'll find a flame sensor that uses flame rectification to detect the flame, but in older standing pilot style furnaces you'll find a thermocouple which "senses" the heat by use of a thermocouple that produces a small voltage when heated.

[@InShortSight]

tech conn pinned a comment on this point. Electricity is weird!

[@collinpearsall9084]

​@@schellenbergenator That's true. Should have specified I was talking about the flame sensor highlighted in that particular part of the video. Having looked inside a very similar furnace I knew it was of the flame rectification type.

[@markdickson2150]

I love the matter-of-fact sign off in this one. "Ok, bye!" :)

[@Dansk55]

Very well done. Learned quite a lot after fixing my furnace this year

[@AsloAso]

I’m in Australia, we normally have wood fired, central heating or as what my home has is floor heating via running a fluid through tubes under the floor for each room allowing the heat radiate up from the floor. It feels lovely to get out of bed and walk to the toilet on a warm wooden floor at the middle of the night.

[@AirbusA380DIA]

Modern mountain homes here (I live in Colorado, USA) have floor heating because there's no need for central A/C if you live in the mountains. It's a cool idea isn't it.

[@PhazonBlaxor]

In Finland we use wood, oil or just plain electricity for heating. In north wood is very commonly used. My father has a huge oldschool stone furnace and it takes a lot of wood to warm up, but it stays hot for a long time once warmed up.

[@thefixerofbrokenstuff]

In the Missouri Ozarks most of us grew up with wood heat. Alas, the influx of foreigners from Illinois, California, and other communist territory diluted the intelligence quotient so much that most insurance companies refuse to insure houses that heat with solid fuel. The risk of fire from stupidity is just too great.

[@jamesarber904]

Another Aussie. To clarify "Central heating" is our term for the gas furnace ;D

[@m2heavyindustries378]

To clarify, the vast majority of Australia is too hot for any kind of dedicated heating system beyond an electric resistive heater/reverse cycle AC. The comment was referring to the colder/ more southern states and cities.

[@jamesplotkin4674]

As a child, I thought adults were saying, "four stare" heating. So, when I was cold, I'd look (sternly) at the register a few times, but alas, nothing happened.

[@lutyanoalves444]

thats cause you never actually TOLD it to get warmer after staring. i bet the poor thing though you were going to beat it.

[@jackhung6929]

The first models worked kind of like a clapper - stare ON stare OFF, but early adopters found the system too unstable. It could be set OFF with a passing glance. It was Benjamin Franklin who came up with the "double stare" variant, known today as "four stare" as most users do not wear glasses.

[@jrb_sland5066]

Many thanks for this video! Last week [2020 11 03] my 29 year old 80% efficient gas furnace was replaced with a 96% condensing furnace very similar to yours. Your explanations give me a better understanding of what is going on inside this cute new machine - the installer guys were too busy doing their work to give me a detailed technical lecture on modern furnaces. LOL It was indeed expensive, but my gas supplier [Fortis B.C.] is currently offering a double-rebate [$1400] so my net cost will be acceptably low once I receive the rebate check. BTW, my detailed gas bills show that the B.C. carbon tax I pay is roughly equal to the basic cost of the methane itself. All else are charges for GST, PST, storage, transportation, etc.

[@shadowxxe]

I live in Scotland and usually (this is true for most of the UK too) we'll have a boiler and radiator system, and since our boiler is downstairs the exhaust pipe is located on the side of my house in the back garden this means that not only does it get a little steamy back there, but it also smells like used gunpowder, of course, that's only if the boiler is running full blast, the insulation is quite good so it only runs when the ambient air temp drops below a certain threshold

[@network_king]

A relative had a new furnace like this put in years ago now, like 6 months after it was in in midd winter it was cold in the house. They looked at it could not find issue, called installer said something is messed up with this thing you installed fix it. End up being (what they said was common issue) a bird sat on the vent on the roof, the Co2 made it pass out falling down the chimney. Then somehow the bird made it into the draft inducer stopping it from running. They later had a cap put on the chimney so this does not happen again.

[@absalomdraconis]

Why didn't it have a cap by default???

[@lutyanoalves444]

@@absalomdraconis santa gotta come in somehow

[@jochenstacker7448]

What is a furnace? Well, it's a flamethrower in a box.

[@HappilyHomicidalHooligan]

With a fan...or 2...

[@Archgeek0]

and a computer to make it turn on and off and not make anything explode or poison everyone.

[@samerm8657]

This is the FORCED air furnace, that you've just described 😉

[@beacjere284]

@@samerm8657 now you are just forcing the topic XD

[@monad_tcp]

@@Archgeek0 there's computers? that's the most unsafe part of it all

[@eustatic3832]

nice! thanks for adding the bit on particulates and respiratory health!

[@Sam-rf8yh]

This was excellent. Thank you so much.

[@kirbymarchbarcena]

Now we know why Santa Claus refuses to go into a modern chimney that has this kind of technology.

[@Stoney3K]

Because it... sucks?

[@Jemalacane0]

@@Stoney3K It doesn't.

[@Kylefassbinderful]

This was extremely fascinating. The last time I learned this much from a Tech Conn video was the part in the Compact Disc series when he discussed how CD's organize data in packets with redundancy and sub channels (not pits and lands representing 1's and 0's like it's easy to think) and are then reorganized by the player in such a quick time.

[@tbituner]

Really loved this video! Always wondered exactly how a gas furnace works. We had a boiler from the 30s in our house when we first moved it and it was literally a gas stove in the middle of a coil of copper tubing that the water flowed through and then was pumped to the radiators. Insanely simple but something only like 60% efficient. Replaced it with a modern combination boiler/instant water heat to keep the radiators and it was tested at over 98% efficient. Only drawback is you definitely need a humidifier with that system; speaking of which I watched your video on that too and love it. My vote is evaporative for anything more than a bedroom.

[@NickCharles]

As someone who lives in a tropical climate where a lot of our homes and apartments use solely electric heat (or heat pumps for newer constructions), this is fascinating to see.