Residential Ductwork : HVAC Duct Design Basics

[@mattcarwin1851]

Talked to a dozen hvac guys and watched double that many videos and this guy solves it in 6:33! Thanks!!!

[@HVACBee]

So glad the video helped! Thanks for watching and for the feedback :).

[@danbrown5133]

Tell me about it☹️

[@ronhampe]

Never talk to local trade people if you want honest answers. Most are scared to death of losing jobs to DIYer's.

[@brygram]

Easy to understand, step-by-step explanation, well-paced. Corporate trainer candidate! Thank you, Adam!

[@HVACBee]

Thank you so much. I really appreciate the positive feedback. :)

[@Dan-hd3cs]

I'm a mechanical engineer that is designing my own HVAC system. This video was very helpful since they don't teach us standard industry practices for duct design in college.

[@will_hunt_music]

Amazing simple tutorial! Great job!

[@HVACBee]

Awesome! Thanks for the feedback Will! Appreciate you taking the time to leave a comment.

[@chrisharris9574]

Thanks, you explained this better than any other video I've watched. I'm trying to do a DIY Ductwork to save some money on adding heat to a basement project. With the crazy prices of everything, we got to do some DIY where we can.

[@harrisric128]

Not all super heros wear caps! Great stuff here bro. Much appreciated!!

[@bushballistics329]

This is how I always done it. 2x 4 supply airs= 8 8+2= 16x8 duct. That would be my first section of duct coming off my upper Plenum. Let's say coming off the front. That would be the closest heat runs next to the very furnace pretty much. Let's say I got a few more further ahead so now I wanna break it down. I'm only gonna have 3 coming off that duct. 2x3=6 +2= 12x8 duct. (Always x2 +2 ) keep breaking it down further in your path. Try to make those run straight into whatever duct. Make it pretty! Less elbows, the better! Now your return air duct . 3x RA+ 3 . Break it down if you have to. Single supply air ran in 6 inch round pipe and double supply air ran in 7 to 8 inch. always run metal all the way up to the return air inlet grill or supply air dampered register. Always put a damper in your duct right before your first supply airs. Around damper in every supply air 1 foot or so off of the duct. Try not to have them at the floor boot as they loosen and may vibrate. That would be annoying For a supply air duct, never ever tap off the endcap. This will jack your flow all messed up. That air has to ricochet off that end cap then it will go to the supplies. Return airs can tap off the endcap. That one's just pulling air back to the furnace. If you have to split your supplier, air duct or return air duct midway then you need a pair of pants. That's a different story. That I could keep going, but this tinner mommy is tired😂🤣😂 journey, mama From Minnesota. That's the easy way. I definitely recommend a professional!

[@ccarlley]

I'm not an HVAC person, just a homeowner that wants to redistribute my existing airflow to remedy a temperature imbalance in my shop. I have 10" and 8" flex duct in the wide open attic space. 4 supply registers are near the plenum and 5 are up to 30' away. Is there a temperature change compensation factor for distance from the air handler? All I see is CFM calculations. Thank you!

[@viper22304]

thanks for sharing the awesome video. Question: what the size of the supply plenum on the furnace is?

[@HVACBee]

You can buy multiple size supply plenums but you’d want to buy one with the same dimensions as the furnace or air handler you are connecting to.

[@omahatim649]

I installed the trunk line above the living space because the upflow furnace is on the same level and I was told it was easier to move warm air than cold so I built in air valves based on this. Anyway, Adam mentions that putting ducts by windows creates crossflow, which I have done, but he says this is to block "heat infiltration areas". Is this also the best for block cold infiltration areas?

[@HVACBee]

Yep, same concept. To get the ‘cross pull’ though, you need the return vents across the room from the supply vents that are covering the windows or (heat / cold) infiltration areas.

[@baggedhemi8705]

Thank you brother ! I’m in the HVAC Service field and interested in the Installations thank you .

[@HVACBee]

Matthew Byam absolutely man! Hope the video helps and I am going to have a lot more to come here shortly so keep an eye out for some more training vids :)

[@javierdomenech4370]

Thanks for the info. I have a 900 sqft house there's a 2.5 ton with 6inch flex and doesn't cool the house hvac is in the attic

[@adamstasevich]

Hey Javier, what area are you located in?

[@javierdomenech4370]

@@adamstasevich florida

[@HVACBee]

How many of each duct and what sizes of each on the supply and return sides? I’m happy to help 👍

[@javierdomenech4370]

@@HVACBee 6 outlets 6inch . 1 4 bathroom 20 return

[@joeybrazda364]

In this example, if the air handler was located at either end of the ductwork would I need 26x8 or 10x20 starting duct to match the 1200cfm required for the system to operate properly?

[@elenawalczyk5927]

Thank you for the video, exactly what I was looking for getting ready to replace ducts

[@HVACBee]

Glad to hear it helped! Thanks for watching.

[@elenawalczyk5927]

@@HVACBee Thanks to you, Adam, I was able to determine what company to trust as the right guys were telling me same points that you did. Others didn’t promise calculations and design options going with “lazy” approach

[@HVACBee]

@@elenawalczyk5927 That is so cool! Very happy it helped and glad to hear it. Thanks again for watching. :)

[@dannytruneh839]

Hi Adam, thanks for posting this video! Will you have time to look over a duct design for my basement? Many thanks!

[@HVACBee]

Hey Daneal, absolutely! Just shoot the plans over to: [e-mail] and I’ll take a look at them for you.

[@dannyt9753]

@@HVACBee you're the best! I'll send my drawing and notes your way.

[@brunomourasilva6247]

What about the return? Some people say that 700cfm is enough for a 3-ton system, but my local contractor said 1200cfm for the return.

[@adamstasevich]

1200 cfm is the required amount for a 3 ton unit, but sometimes the math can differ on the amount of air the actual ducts themselves can move (depending on static pressure.) We use .8 static pressure as our gauge in Georgia which means the 10" even though (rule of thumb is 400 cfm) if you used the more exact math with static pressure calculated in, it would actually only be 320 cfm.

[@JBra1382]

Easy answer. You can NEVER oversize a return. Always make the return bigger than the supply.

[@nojiggle530]

So 1200 cfm is a rule of thumb there are alot of factors that can slightly effect this number and I disagree you can oversize a return when oversized the velocity falls off and you lose dopler effect and thus have a noisy duct system

[@2979paul]

I have a ducted ac and heating system and would like to remove a wall. I need to redo the ducts and would like to create a new riser to the second floor and install the 2 inch high velocity ports in the sencond floor ceilings over the windows. Is this possible

[@HVACBee]

It is possible but make sure to still ensure the ductwork is sized properly for the unit even after adding the new supplies. If you have too much supply space, the HVAC system could struggle to get enough pressure build up (in the ductwork) to push the air to the second floor.

[@jham5595]

Do you need a return box ? I have a 3 ton unit that I made a supply plenum for was just wondering if I neede a return box as well

[@adamstasevich]

Nope, typically you'll only need a return box on a 4 Ton unit or larger.

[@jham5595]

@@adamstasevich sweet so I can go right to my vent in my ceiling?

[@adamstasevich]

​@@jham5595 Yep! You could also build a smaller return plenum next to the system and have the duct run from that as well.

[@jham5595]

@@adamstasevich thanks 🙏 much appreciated!

[@adamstasevich]

@@jham5595 Sure thing! No problem. Good luck with the project :)

[@stevenlaw610]

Fantastic presentation. Easy to understand. Well done!

[@GCRAAY]

I’m a bit confused on the plenum. Mine is a down flow into a crawl and clearly not as big as his example or an example of a down flow I saw on a slab. Although he didn’t say the size. I suppose it could just be mine is shorter but wider. If anyone knows explain please.

[@MG-qk8tx]

Nice job however you should have finished with a floor layout showing the trunk & flexible duct layout. The reason I mentioned that is that it is usually better if you connect the flexible duct toward the end of the trunk such that it works more like a plenum. For instance, if you do your 1st 6" flex duct say at 90 degrees off the trunk maybe 3' from the start & the 2nd one say toward the end, 10' in this example, the 2nd one will have much more air flow than the 1st one.

[@HVACBee]

Mike G definitely! I may even make a advanced residential duct work video or something along those lines to elaborate a little more 👍.

[@idanny76]

I have high static pressure on a new 3.5 ton heat pump. I know for sure the flex duct is the issue. I have two 12" coming out of the supply in opposite directions. I know I need an 18" for a 3.5 ton heat pump. I did a diagram layout of the duct in the attic. What would happen if I just replace the two 12" to 18"? Ignoring the downstairs, because everything is between the walls. The problem was even worse with an undersized return. The original and only return was a 24x18. The total static pressure on the unit was .9 W.C. I was able to drop the TESP to .66 by making the return 30x24. Since there is so much static pressure and the unit TESP is a .2 and I need an 18" for a 3.5 ton for 1400 CFM. How big does the supply plenum should be and what shape? Should the supply plenum split to 3 18" going out to each of the 3 distribution boxes? Do the other three distribution boxes also need to be larger? Looking at the triangle shaped supply plenum I have very little room up for a rectangle plenum. I think a 3 feet ductboard supply plenum should work. There is a foot from the Air handler to the ceiling and I think 2 feet from the attic floor to the roof. Now I am looking at two types of designs. Design #1 keeps the 18" ducts straight by having a single 18" coming out of the supply and then a distribution box splitting it to three 18". The sides would be coming out straight to the to side boxes and one going to the third box with a slight curve. Design #2 splits to three right at the supply plenum and goes to each box individually, but all three will have a slight curve. I will not be using any metal plenums..... it will be all flex duct and ductboard boxes, because of budget. I am not trying to make a perfect system, but trying to remove the restriction from the 12" undersized ducts installed and replacing the flex duct that was patched with mastic with new ones. Another question about the installation..... I have the flex duct running up and strapped to the roof for support. Since the supply plenum is low to the floor due to the roof..... Can the flex duct be run on the attic floor? Can you tell me which layout makes more sense and less restrictive? Thank you. Layouts: Current i.ibb.co/Ld9kmPM/Flex-Duct-Layout-and-Size.jpg Option #1 i.ibb.co/GHyS00g/2022-07-05-0002.jpg Option #2 i.ibb.co/PNN8mSB/2022-07-05-0001.jpg Air Handler Specs ibb.co/17VvF4B Video of attic kzbin.info/www/bejne/n3rReoFubtZrfbc

[@ClintChance]

So much information given here I had to break out the pen an paper just to find that the contractors severely messed up. Thanks for the new project 😊

[@trueforum378]

question please: it is clear how to determine duct size WxH, How can I determine LENGTH of that size? thanks for the video!

[@johnbermudez3634]

Fantastic! Exactly what I needed and straight to the point. PERFECT.. Thank You!

[@HVACBee]

Awesome, glad it helped!

[@j.lietka9406]

Here's a good question: can the A-coil be adjusted (it's horizontal position) by removing the trunk (short straight section of square ducting) connecting the A-coil cabinet & the plenum? Have an A-coil that is not sitting like it should. Condensate water 💦 doesn't drain out of the regular drain line, but it drips out of the cabinet. Some I have collecting in a bucket, but some is going into the drain pan. Thank you the heating and cooling system work just fine, but there is a condensate drain problem, b/c the A-coil is not sitting as it should (level) for proper drainage

[@HVACBee]

Hello 👋. Shoot me an email with some pictures / the same info above and I’d be happy to help! [e-mail]

[@philiprogers8620]

This is exactly what I was looking for, great explanation, thanks!

[@HVACBee]

Glad to hear it helped you out! Thanks for watching and don’t forget to like and subscribe :).

[@mexican12OS]

How long would you recommend the trunk lines?

[@JBra1382]

Depends on the house. And length of supplies

[@HVACBee]

If you’d like to shoot me an email with some additional info I’m more than happy to help. [e-mail] 👍.

[@JR-bi3hr]

I can’t find the chart is it still linked with this video?

[@DailYxDosE]

4:20 I’m confused. Where are you getting the (2)8” + (1)6” =500 from? And all the other ones. 8” by what? 6” by what?

[@willskora2055]

I’m thinking diameters

[@HVACBee]

Diameter of circular flex duct 👍. This is a flex duct chart example that is shown. You can also search a ‘rectangular duct chart’ to see the cfm for those sizes as well though :).

[@igorvolkov4056]

Revit dont understand how much air needs from room?

[@HVACBee]

With the project we are starting in Holly Springs, the designer used Revit, and I do not believe it gave a AC tonnage requirement for the space like you said.

[@libertus8924]

Does anyone know if it matters where you install the return air filter - whether at the back of the return air duct close to the furnace or at the front of it about 18 inches from the furnace?

[@kcomfortsystemshvac7060]

Adam,,,,good man,,,👍👍 nice video...for,,this 1.200 CFM ,,,,, how do I get the size,,for the register supply and return ? Can you do basic video,,,?

[@HVACBee]

Absolutely! I have another few videos I am working on now and will add that to the list :) thanks for the feedback

[@gregburns8099]

I am a new residential installer in the Midwest looking to move into design and layout. There are many things missing in your video that I have been taught were needed. Reduction of duct size along the run for pressurization. Friction difference between flex and hard pipe. You didn't even cover return systems. What about differences between brands? I'm just curious.

[@HVACBee]

Hey Greg, your absolutely right! There is much move to residential duct design than this for sure :). I wanted to just cover the duct design basics and in the future am planning to make additional videos to elaborate further 👍

[@hangngoaigiare]

so i want to get hand on training on laying out ductwork. do u do that for a fee?

[@HVACBee]

Hey Quang, I am happy to help. If you are still interested, shoot me a quick email and we can figure something simple out. [e-mail]

[@mikejohn8129]

Hi Adam I have a questions total 1700 sq house the size first floor is 25ft Width by 30 ft length and the first floor ceiling height is 9 ft tall and the furnace is to the other end basement not in middle the house ,and Upstairs 4 room all the size is equal 12 ft by 13 ft and ceiling upstairs from the floor is 8 ft tall .what is the size duck work ? Here I used Rectangular 8 inch by 16 inch and 16 ft long but it couldn’t reach upstairs floor

[@gilbertocrespo7721]

I am planning to install a new American Standard 120,000btu (5 ton) Up flow furnace (S9V2D120U5PSBB) and the HVAC designer said I need a return box placed under the furnace (code). I ask Him what would be the height of the box and he said it would be 6" X 28".75 X 24.5". The question I have, with the 6"height, that will cut down on the height of my plenum (17" - 6" = 11"). Is there a minimum height that a plenum has to be? Another question, with the main supply (14" X22") and elbow opening into the filter housing (20" X22") and other side of filter housing going into the return box opening (6" X 20") are you choking the air flow going into supply box? Is the 11" plenum allowed? Great video.

[@user-tr9to2bh6x]

thanks ..where chart in description ?

[@jemalwright3414]

Excellent Video!

[@GrizzlyAir-MT]

great video, but i don't see the duct chart link lol

[@HVACBee]

Hey Sorry about that Adam! Here you go. hvacdirect.com/hvac/pdf/Field_duct-sizing-chart.pdf

[@troybowen9277]

I'm finishing my basement and the ceilings are already low. Is low profile ductwork an option? What needs to be considered if I switch to low profile? Do the dimensions of the ductwork just need to total the same? For example could a 14" x 6" be made a 28" x 3"? Thank you!

[@HVACBee]

Hey Troy, here is a link to a rectangular duct chart. I think this may be able to help you out if you haven’t started on this project yet. hvacdirect.com/hvac/pdf/Field_duct-sizing-chart.pdf

[@guitarhvac]

Are these CFM figures you're using based on 400 FPM. I'm trying to get a good grasp on this ductwork sizing stuff, but seems like there's some info left out or just an assumed FPM number most guys are using when teaching. When someone says, "this size duct can handle this much CFM" I'm thinking, "Yes, at a set velocity of xFPM." But if your FPM changes does the CFM not change....??

[@HVACBee]

This is just the basics of residential duct work, but it is assuming a .8 static pressure which is going to depend on the length of the run, type of duct material, etc. :) If you have any additional questions, I’m happy to help. Feel free to shoot me an email with any additional info or questions. [e-mail]

[@coreymadden3650]

Great video man! Exactly what I was looking for

[@brunomourasilva6247]

Hi, nice video. can we split the trunk cfm the way you did, like left 500cfm and right 700cfm? My truck is 8" x14" on both sides of the plenum but the HVAC guys told me I need to increase my trunk to 8" x24", they don't consider left and right on the calculation. I will install a 3-ton system.

[@SA-rt6ei]

Howd that work out for u lol

[@brunomourasilva6247]

@@SA-rt6ei I installed a 3-ton system; it works, but it's not efficient. The heat on cold days does not go above 21 Celcius, and I have to use a low Merv filter.

[@michealmonteiro7127]

Sir how to construct Round duct Pleanum box.?

[@hvacguy11]

How do you determine the rectangular duct height though. Like 6,8 or 10inch

[@helipadny1]

So? Probably a totally stupid question !!! I'm designing a duct layout for a 2 ton system for my small house. The AHU will be centered with the house, I'll need (approx- 500 cfm's on one side of the house ,, and 300 for the other half,,, Would I be correct in sizing the trunk accordingly for each side? The trunk for for 300 cfm's come out to roughly 8 x 8 ( with a .07 friction rate ,,, calculated , not assumed !) Only Asking because I've searched like crazy, and this is the only video I've seen where you've split the load,, ( make's sense to me btw,,) Just want to make sure I size accordingly ,, I've searched at nauseum, and every example shows one main trunk and sizing down as needed, so, I'm a little confused with that part, Otherwise ,, its approx ,, a 8 x 20 trunk straight across ,for a 2 ton/800 cfm's unit ,, if I'm using the calculator correctly :) 🤔 thx!!!

[@chr0meh34rts]

thanks for this!

[@benjamincordova1404]

Amazing video

[@HVACBee]

Hey Benjamin, glad it helped!

[@fatbol526]

Amazing breakdown I appreciate your time and knowledge

[@HVACBee]

Thank you! If you ever have any additional questions or anything just let me know. [e-mail]

[@jham5595]

How would I figure out the return duct size??

[@adamstasevich]

Same flexible duct sizing on the Return side. Rule of thumb: (1)6" = 100 cfm (1)8" = 200 cfm (1)10" = 400 cfm (1)12" = 600 cfm (1)14 = 800-1000 cfm

[@jham5595]

@@adamstasevich cool thanks so much!

[@mexican12OS]

Freakin awesome best video about this subject. Thankyou

[@HVACBee]

Thanks so much! Super glad it helped you out 👍

[@laynelommen9460]

Great video. ❤❤❤

[@HVACBee]

Thanks for checking it out. Hope it helps a little with your HVAC journey.

[@nojiggle530]

Not trying to be negative here but this is why we 10 out of 10 systems have air flow problems. The design is garbage in garbage out, and the first fitting destroys all the flow and will never balance. We all need to start taking this seriously

[@justingowan601]

Thanks for this!

[@HVACBee]

Sure thing! Glad it helps :)

[@saifshareef7194]

Thank you

[@pcngo1]

Thank you!

[@HVACBee]

Happy to help!

[@kidsareblessings1608]

Thanks bro

[@HVACBee]

Glad it helped. Thanks for watching!

[@dan8220]

What happened to ya, 3 videos and stopped?

[@HVACBee]

I promise more soon!

[@rhiczgartv3410]

Ilove it😍😍😍

[@HVACBee]

Thanks for the positive feedback :)

[@frankgall6]

Rule of thumbs have messed more systems up then you could EVER imagine

[@HVACBee]

Definitely agree. ✅ Always want to run a load calc when possible and ensure there aren’t any other issues with the installs application prior to the project.

[@pjandbmx]

@@HVACBee Which is EXACTLY how to started the video, with that explanation. You did a GREAT job of providing a clear and concise, "rule of thumb" overview, which is exactly what many people are looking for.

[@HVACBee]

@@pjandbmx thank you. I really appreciate that :).

[@TreRealLifeENT]

Thanks bro.

[@SA-rt6ei]

That 12x8 and 16x8 coming off plenum for 3 ton system is too small

[@HVACBee]

It is about 1300cfm before deducting static pressure. A 3 ton blower and coil needs 1200, but if there were super long runs, and a lot of them, you could need additional 👍.

[@philllsxga.7737]

Flex duct?!? That's a cuss word from where I'm from 😂🤣😂

[@HVACBee]

Where you located? We see it probably 90% of the time in north GA. Definitely not the absolute BEST choice, but definitely the BEST economical choice.

[@philllsxga.7737]

@@HVACBee in the north... If you mention flex to the guys I've worked with and learned the trade from they would tell you to leave.. Flex is such an flow restrictor. Remember the right furnace for your home is the one that's installed correctly I don't care how efficient the furnaces if it's choked down with improper size ductwork you just blew the efficiency out the window...

[@bish331]

400 per ton

[@buckslaughter9014]

Uh ok. So static pressure is irrelevant

[@HVACBee]

Not at all. I mention static pressure but it changes based on circumstance (length of run / material type) so I used the numbers prior to static pressure loss.

[@buckslaughter9014]

@@HVACBee ok gotcha.

[@yasuhiroy6585]

only theory , no implementation, difficult to understand for the beginner bro.

[@Parabellum-X]

This dude looked nervous as f#@k. Great instructional video though.

[@rockycomet4587]

I bet his knees were knocking.

[@jasonprater22]

3 ton is 1800 not 1200

[@willskora2055]

Three ton needs 1200 cfm is what he is saying. Three ton of cooling for example is 36,000 btus. The 600 was the area to condition, and 600 square feet needs 1 ton of cooling. I think I got that in line to what the example covered.

[@HVACBee]

Hey Jason, I have never seen anything other than 400cfm per ton of the drive of the blower motor. Can you please share where you are seeing 1800 for a 3 ton?

[@SpiLViL]

Basement😢

[@williammarik6159]

Jeez. If you,ve been doing this for any appreciable length of time,these convoluted formulas are not required.

[@davidcbrown4376]

Nothing about this guide is of any value other than in the beginning when he said to do load calculations. EVERY "rule of thumb" mentioned is of no value. Also, if you don't know how much air is supposed to go to each room, which you don't without load calculations, how can you determine the correct size duct/s to route to that specific room? HINT: You can't.

[@Hardworkwork777]

400 CFM per 600 ft^2? Wow, I don’t think so, bud. I think your engineering is off by a bunch. Typically 1 ton per 400-500 ft^2. Trust me, it makes a big difference, especially when you have gatherings.

[@blazedNdazed420]

It's 1 ton per 400-600 square feet. If you live in a high humidity area like the south then you go towards 400. His 600 statement is still true.

[@bojangles_bonjangles8000]

New houses decently built are closer to 750 sf / ton

[@jaredking8690]

Oh dude no please

[@harryboody]

Surely this is a joke.

[@Gutter-Snipe]

nice salesman training vid, as to how to supper simplify for the customer. i am guessing you are no more than 3 years in and have a lot of potential in sales. If your trying to show the masses how to calc and size ducts you have miss some of the most important things. you used a bad rule of thumb for older homes and homes built in the last 30 years 600 SQ per ton is not for every house. then you skip load OK not recommended by any Pro, but then you don't explain total effective feet of the duct as you have it layed out , you dont tell the most important part of what friction rate is left after pressure drop of filter coil , to even select a airflow for any of what you had in the vidio. take some more air flow clases and if i am wrong and you know more than this vid then stop posting half ass vids to confuse DYI people.

[@Paul-o-ween]

It’s an intro video for a very basic understanding. Clearly not for pros. Maybe before you start recommending classes people should take you can take a basic English class yourself.