Manual J Deep Dive (and Selecting HVAC Equipment with Manual S)- Part 1 of 2

Alex Meaney is my trainer when I level up on HVAC design calculations, and he came to visit us and share some of his expertise. Alex reveals what the J stands for and why you should never round up the tonnage from your Manual J software, and gives two rules for Manual S:
1. Never use AHRI data
2. Meet the latent load while not going too far over the sensible load (more in part 2)
Check out Alex Meaney's trainings: MeanHVAC.com
ASHRAE Weather Data Map: ashrae-meteo.info/v2.0/
Watch Matt Risinger's video on the Build Show about my Manual J report tour:
• Your HVAC specs might ...
Learn more about the Science of Homes: BuildingPerformanceWorkshop.com
Watch the first-ever TV series about the Science of Homes: HomeDiagnosis.tv

[@edlauren9434]

I am a licensed hvac/refrigeration contractor. Great video, thank you! Since I’ve passed my license exams I’ve re-done air ducts at dozens of residential and commercial properties. Dozens and dozens!!!! Here is the typical story… Customer says that his convenience store/gas station don’t have enough A/C during July/August. So, the customer wants one more 5 ton RTU installed because people behind the counter literally sweat badly as soon as outdoor temperature goes above 90F. So, I re-do the entire air duct set-up and…. There is no need for additional A/C anymore, the electrical bill drops 30-40%, no sweating any more… So, with the ducts done correctly, old bitten up A/C becomes surprisingly efficient. P.S. I’ve tried to use the manual J for my air duct designs …. and I gave up on using that Manual J because it more confusing than helping. :) P.S. #2. I now have a line of small shops, stores, restaurants that are willing to get the air duct see-done.

[@HomePerformance]

Good work Ed- and yes, Manual J is probably not the right tool for you in commercial spaces.

[@E150GT]

Crazy stuff. Being a homeowner I have read enough to be dangerous. I asked my contractor to downsize my equipment when he replaced it and he didn't put up a fight or do any calculations. He just did it. I had my reasons and I think it's gonna be ok. But holy crap what a gamble I took without knowing what the hell I was doing. And still don't. I find this stuff fascinating and disappointing at the same time because I would probably venture to guess a lot of HVAC professionals don't even get this deep.

[@HomePerformance]

I love this

[@cindystokes8347]

They have no incentive to. They make more when it’s oversized and they don’t pay your bills.

[@TECTubefilms]

Meaney and Corbett in one video! Couple of our favorite instructors.

[@ryanhoger1]

These dudes have so much energy and passion when they talk. I loved when Alex comes to town each year to teach Wrightsoft classes and I eat up all of Corbett's podcasts even on topics I don't really need to know much about. Fantastic combo. More please.

[@timdestasiohvac]

I love listening to Alex Meaney talk design! I'm glad to hear experts like him acknowledge there is still a level of estimation in HVAC design. We can do a lot of things to reduce the ductwork such as inserting the blower door ACH instead of picking "Average" or "semi tight" infiltration, but things like duct gain are just multipliers- SWAG at best.

[@justinherman9443]

Wonderful video, can't wait for pt2.

[@paulmurray3837]

I love that you back up your comments with actual data. Thanks for the info.

[@HomePerformance]

Rock on Paul

[@ryanhoger1]

The link to the ASHRAE weather data just saved me a ton of time instead of looking it up in the actual ASHRAE Handbook each time. I have been an ASHRAE member for 20+ years and never knew about the site!

[@davec6016]

Alex Meaney talks and has mannerisms just like my brother-in-law who is fascinating to listen to just like Alex. Of course, Alex is talking about subjects my brother-in-law has no clue on, but are extremely interesting to me. I was in HVAC service briefly decades ago between my Army time and college. I grew up in a house with a father who believed only in window units and radiator heat and thought central air was the devil so I was slow to the game. Since working in apartment maintenance in my youth and spending a year learning how to repair all the gas furnace central air systems on the property I have always held an interest in moving heat around, but never went that route for a career. One thing i definitely learned is just because a guy shows up in a van with a state license # on it, there is no guarantee he has much of an idea of what he is doing. This was clear when i was a young apt maintenance worker bugging the HVAC contractor we called with questions and he couldn't even tell me what the difference between PSIA and PSIG were. He also had no idea how a capacitor worked. I wasn't being a jerk. I didn't know either and was honestly curious. I found the answers on my own that night, but that service tech likely still doesn't have them. I pretty confident Alex could answer any questions i could come up with and answer questions I didn't even know i had ! A ton is not 12,000 Btu's and J is for 'joule'... marvelous. Great video.

[@mzzm8850]

So glad I'm learning this now before I try and figure out our geothermal project. I'm getting so much bad information from folks in CT after doing some basic research. I'm pretty sure we will be reaching out for further building science reco's.

[@MattPetrowsky]

Way cool stuff. I'm actually glad my personal build has been delayed because of inflation, trade access, etc. I keep learning more cool stuff like this.

[@davidhoover2446]

I need to do this or have it done by someone when we replace our A/C. We have a 2,000 sq ft house with a 2 stage 4 ton A/C installed by an A/C contractor chosen by my builder. We literally never need anything except stage 1 at 2.8 tons even on unusually hot days over design temperature of 91. If it's 96 out and we're cooking, and we're running exhaust, and maybe also drying clothes then it will run 100% of those times still maintaining 74 on stage 1. It's a huge A/C for the house and it doesn't run a lot. I have installed a ventilating dehumidifier and dialed in the fresh air to keep the VOC's and C02 at a good average and it keeps us dry when the A/C isn't running. Our oversized A/C plus the dehumidifier now works well together.

[@adrianwright3061]

Thanks very helpful and informative. The new hvac curriculum has began.

[@HomePerformance]

✊

[@frankgall6]

I’ve watched it 4 times already lol a lot to take in, great job as usual 🎉

[@HomePerformance]

Thanks Frankie buddy

[@Squay313]

This is such a great episode

[@HomePerformance]

Thanks Jamie

[@Studentofhvac]

Great video. Alex is a beast!

[@petersonfam77]

Alex Meany is the dude.

[@Joe-qw6il]

This is good stuff, I’m getting ready to re-design my ducting system in my attic, contractor who built my home did a horrible design job!!!

[@Crusader1815]

Alex is one of the most knowledgeable people in this field, and his training is really valuable. I can't help but think, though, that he and all who are listening to him could benefit if he would modify his delivery. Maybe it's a Boston thing, but the consistent snarkiness makes it difficult to listen to him.

[@davidhoover2446]

Thanks for the information

[@TJ-22]

Two very knowledgeable and talented individuals. Excellent video. The video mentioned it’s not a good idea to set a thermostat below 72°, because on a peak outdoor humidity day, the outdoor dewpoint could reach 72° or above. If that happens, when the indoor air and outdoor air meet, condensation will form indoors, usually in areas that are hidden, where you can’t see it. Therefore, if we keep the house too cold, we risk condensation forming inside the ducts, on the equipment, in the walls, the ceilings, and hidden in places that we can’t see. In the southeastern US, it’s not uncommon to have Dewpoint temperatures at 75°. On the other hand, if we keep the house too warm, we risk the dewpoint rising. During the time that the AC is off, humidity from the outdoors is infiltrating our home. Which could cause condensation to form on the AC vents, potential mold growth, in addition to possible structural issues. The longer the air conditioner pushes cold air out of the ducts, in an environment where the surrounding dewpoint is higher, The more sweat that will form on the surface of it. It can be a challenge to find that perfect balance.

[@HomePerformance]

Thanks TJ, well said

[@TJ-22]

@@HomePerformance Thanks

[@martinp1544]

Great info! Thanks!

[@HomePerformance]

👍🏽

[@MarkRose1337]

I keep the temperature at 15°C (59°F) in the winter. Any below 13°C (55°F) gets a bit chilly. I could really use a humidifier, too.

[@albertoarriaga9611]

Hey Corbett, awesome content. Where can I find the extended OEM data/design condition calculator for Mitsubishi systems?

[@marvingarcia8982]

Great information but one thing they forgot to mention is that all manufacturers are doing inverter compressors and at that point your 3 ton could perform as 2 tons if outdoor and indoor temp requires that, and yes will have to have a good duct design but the conversation here was manual j and equipment selection. As a contractor I have much respect for engineers. Thank you for the information.

[@alexmeaney2407]

Careful. Not all inverter systems are created equal. Many systems (especially multihead applications) can't ramp down nearly as much as we think (unless they are true VRF). And even the ones that can ramp down by a lot aren't always a very good solution without dehumidifiers as some tend not to dehumidify well (or at all) as they run at lower capacity- it helps them get a higher SEER score but can be a humidity nightmare in the wrong situation. At the end of the day, there's no substitute for looking things up. I think we talk about some of this in part 2.

[@winstagram1785]

Big problem we’ve seen in the last couple of years. The evaporator doesn’t always reach dew point when it’s running in a lower speed, so it’s reaching sensible set point, but not removing any moisture. Also, ducts should be designed for when the unit is running at 100% capacity. You lose the stratification effect if the air velocity is too slow. I believe the top tier Trane units allow you to set humidity along with temp and it will ramp up the compressor to a high enough speed to still reach dew point even when sensible is satisfied.

[@microcolonel]

To nitpick: a joule is a unit of energy, but your load is quoted as power (ton/watts) since it is over time. E.g, a Joule being one watt-second (energy), a ton being 12000btuh (power) or about 3.5kW Good note on the equipment, and how conditions completely change the performance of heat pumps.

[@Werdna12345]

First time I’ve heard don’t set AC lower than outdoor dew point

[@tweake7175]

i absolutely love that you guys mention "ignore what temp the customer says". the human factors side drives me nuts a bit.

[@scottschweigert1657]

oh hey at @5:10 thats gonna be me lol - debating signing up for a session cause no one here in Hawaii wants to do ducts and im afraid of sizing a system too big it doesn't get rid of humidity.

[@brightboydesigns8325]

I would like to hear your opinions on the CoolCalc Manual J web app as well as how to best reverse engineer/optimize/pick new equipment for an existing system in a 20 year old house where so much of the ductwork cannot be changed/altered. Manual J/S/D guidance from ACCA is great for new construction when you have new construction.

[@HomePerformance]

If the ducts cannot feasibly be altered, then you’re right, a block load is all you’d need to make sure you don’t make a mistake replacing the equip with the same size. Luckily, if the equip gets downsized bc of improvements in the enclosure, the ducts are upsized automatically, which never hurts.

[@brightboydesigns8325]

@@HomePerformance You should also consider partnering up with Ed Janowiak who is the head of education at ACCA and has his own KZbin channel. His lectures are also published on other HVAC KZbin channels like HVAC School.

[@HomePerformance]

Thx Bright Boy

[@diaperdood1]

I have 3.5 ton heat pump in a 1500 square feet house with blown fiberglass. Now I have spray foam in the attic with the fiberglass removed. A manual j was performed and recommends a 2.5 ton. Can I just use the 3.5 ton heat pump already in place and use a whole house dehumidifier? Thanks!

[@howardmeeks3143]

I’m not an hvac contractor but I have a decent understanding of it. I would imagine you could use your existing system and use a whole house dehumidifier to keep the humidity levels where they should be. The issue with oversized units is they won’t stay on long enough to remove the humidity. It’s going to cost you a few grand though to have one installed unless you did it yourself. In my area you could probably get a new mid range 2.5 ton system installed for $5k so it may not be cost effective to go your route in the long run. Whether or not you can use a system that’s one ton smaller with the existing ductwork is something you would ask a hvac contractor though.

[@AdityaMehendale]

Please don't be shy to delve deep into the "geeky" stuff. The non-geeks aren't watching this video - they are out playing football, or waving flags, or whatever other stuff it is, that non-geeks do. Wonderful explanation about the "melting ice" rationale.

[@HomePerformance]

Thank you and agreed on the metric system

[@JMoney-ne3to]

Great assumption. You sound like a real 'learned' individual.

[@AdityaMehendale]

@@JMoney-ne3to Your assumption, too, is correct!

[@videos10]

Disrupting what we were taught, feels like im learning from scratch again. I even think Corbin learned a thing or two.... I'm Starting to stress out

[@valasdarkholme6255]

... So if you *ARE* someone who overheats, that *really* wants a 65°F House in the winter, but will *compromise* with 68°F - How do I avoid the humidity problems you're describing? Lots of dehumidifying?

[@HomePerformance]

Yes

[@HomePerformance]

And airsealing, and insulation- it’s a system.

[@ZergZfTw]

@@HomePerformance Using a perfect wall style construction helps a lot. If all of the thermal resistance is on the outside of the air control layer, there is a lot less stopping any moisture in the wall from evaporating to the inside, where it can be dealt with by the dehumidifier. Using moisture insensitive materials, CMU, mass masonry, ICF, and even hempcrete works too; rocks and concrete don't tend to have any problems with getting a bit wet.

[@MrNiceGuyMEGA08]

What is the order of HVAC manuals? Is J 1st? Then S? Then D? Are there any more?

[@HomePerformance]

Correct- J, S, D. There are more, but if you can get these done you’re aces already.

[@aldoogie824]

Are you literally reading this comment and haven't hit the like button, literally the easiest thing you can do for the channel.

[@HomePerformance]

Aw shucks, thank you Al

[@noahoyeah]

Just wacked the like button. Thanks for the great videos

[@HomePerformance]

Thanks Noah

[@f.villanueva]

🥰🥰🥰

[@ccvideotech]

Florida... December...88% Humidity.😑

[@HomePerformance]

Haha yes- but interestingly, most places are very high RH in winter. Because it’s cold, RH has a different meaning.

[@ccvideotech]

@@HomePerformance fair point.

[@alexmeaney2407]

Also, much lower dew point, so when you bring in cooler high RH air and heat it up, the RH is still much lower. That said, I don't care what the homeowner says in FL- the dew point is so high on peak dehu days, anything lower than 75 without an intense independent moisture control plan is malpractice.

[@ccvideotech]

@@alexmeaney2407 Tell that to the contractors down here. The homeowners all know but usually not till its too late.

[@kevinkroll5540]

How are you dealing with fact that Elite Software has not updated their HVAC equipment database since Jan. 2019??

[@HomePerformance]

Once I finish with Man J, I leave Elite and do the rest by hand and 3d modeling

[@kevinkroll5540]

​@@HomePerformance How are you doing Manual S??

[@HomePerformance]

If we can get the extended performance data from the installer (big if), then match as Alex describes.

[@kevinkroll5540]

@@HomePerformance Ok so I actually work for the HVAC company doing the install. The only thing we can get is the AHRI number from our local Lennox rep. I guess we need to start asking for that performance data and maybe go through the dealer site like Alex talks about to get more equipment info?

[@HomePerformance]

You got it man!

[@quantaengineeringllc]

Joule is a unit of energy, in this case thermal energy. It can be quantified a few different ways. One is that it is the energy dissipated as heat when one amp passes through a resistance of one ohm for one second. *OR* It is equal to the amount of work done when a 1 newton force displaces a mass through a distance of 1 meter in the direction of the force.

[@paulgaras2606]

Whhaaaat? j is for joule?

[@HomePerformance]

Good to know the nerdy soundbites

[@paulgaras2606]

@@HomePerformance the whole Acca Manual naming scheme has just been unlocked. J=joule D= duct S= selection T = throw B = balance CS= commercial systems N = now we’re talking Q= quit while you’re ahead

[@pyroman590]

I guess I'm that guy, I keep my thermostat either off completely or between 60-65 all winter long.

[@GCRAAY]

Guys guys guys, talk to us like we’re NOT in the HVAC business for 30 yrs.

[@BigAnil]

Living in Houston we set our thermostat to heat to 65 and cool to 72. With the crappy Lennar home we live in the house is always humid, greater then 65% RH. Am I still an idiot 😅

[@seek3n]

All the hvac contractor should quit and go work for this guy.

[@samgreer8596]

Who the hell is this guy? Is he a mechanical engineer? I'm not impressed.

[@GregorVDub]

Just call it a load calculation