Quick and Easy Duct Design Information 

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Finally... a contractor that is not arrogant & will share some great info on common HVAC problems. THANKS!!

SIR I need some help I live in a double wide trailer --I am going to buy a new air condition unit .the unit is just air no heat in the unit .i have a new heat unit in the hallway it has a 10 inch flex unit pipe from one side of trailer to the another side of trailer works great. now if i put a ten inch line from one side of the trailer to other side will this be OK. MY OLD AIR UNIT WAS THIS WAY. YOU NO TRAILERS HAVE METAL DUCTWORK UNDER THE TRAILER --HELP WILL BE THANKFUL

Just a quick tip for those that have no clue this example is for normal size homes (not mansions or anything that big of house) Flexes and they purposes 4” is for bathrooms /private toilet rooms Food pantrys/walk in closets, front doors or mudrooms, 5” normally laundrys or a bedroom where you barely fit a twin or bunkbeds 6” kids bedrooms , living rooms/family room,dining rooms 7” kitchens, dining room,living rooms(will take 2)master bedrooms (will take two) 8” master bed rooms , living room 10-20” are usually trunklines, returns flexes

Interesting. For some reason Most AC companies claim they can engineer duct systems. They fall short. Usually they guess, or want to just change it for new. I am 608 1-3 cert. due to the equipment I work on. Doesnt mean I am a duct engineer.. but it does let me sniff out fakes. My new house has a "new full ac system". It is horrible. with kinks and pinches and sags and loose flex duct. its a mess, doesnt work and drips condensate. YET of the 10 companies I have had come out to Re-engineer the whole system only one has come close. Its sad really.. dont claim to be something your not, especially when someone specified, Especially when you are a "professional".

Nice to have someone like you explaining this stuff.

David, you did a great job explaining some complex details and giving valuable information in this video.

Who cares just slap it in there as long as it's blowing cold air that's good enough right

you can always learn something new from others but you cant teach something that takes years of learning how to do it in one video ,, all this does is leave people with more questions

So it sounds like if you use flex verse metal duct you reduce the volume by 50%. for calculating size of duct. So using metal I could use 6" duct, If I use flex I need 12" duct?

Manual d is the proper way to calculate size of ductwork. Caution, when using a friction rate it is based on 100' of equivalent length of ductwork. Duct systems should use available static (T.E.S.P. of blower minus everything external of of equipment: coils, filters, grills, etc. x 100/ effective length of ductwork ) to size ductwork.

David I have a question. If I design a duct system for example 4 ton airhandler @ 1600 CFM. I size the trunk line with the ductulator for 1600CFM, should all the flex drops CFM equal 1600 for a balanced duct system?

Sa sa ye la ki santi rans sèk konsa ? Kisa ki aluminium carbide la ? Poukisa yo mete aluminium nan system nan ? Yo pa konen aluminium ak plon se bagay ki dezentegre vit ki pa janm dwe chofe trop paske l'ap gaye an poud gaz nan tounen moun ? Se krack moun vini pran isi ?

I have a 3.5 ton, 13.4 SEER packaged heat pump with an X13 blower and 10KW back up strips. My duct work is single 14 inch flex return, the filter box is a 14x20, the supply is also 14 inch flex that is wye'd off into 2 plenum boxes under the house, each plenum box feeds 5 vents, each supply vent is fed with 8 inch flex, the individual supply vents are 4x8's. All of the flex is black polyester. Does this sound adequate or undersized? I ask because I get a slight whistling from the return and the condensate will not drain if the blower is running even with a P-trap full of water and the bottom of the air handler side of the unit is always wet.

So so wrong on so many levels! .1 on the ductalator? Really? Did you ever hear of manual D? Your a part of why duct systems are so screwed up. Ever hear or “total equivalent feet” ? CFM per room based on BTU loads? Unbelievable! Wayne Schneyer Manual J and D instructor.

You are very good at explaining , Unrestricted Airflow. RETURN THAT AIR !

Loved the information on wider grill spacing, that hasn’t even occurred to me. Thanks for the eye opener

Return grills, versus pass through grills, when and where to use them when and not to use them???

Don't use pleated filters in a house, especially if you have animals or have wood floors etc. You will be replacing them every month. They were made for air cleaning systems, not regular homes. It's a money thing.

The .1 . 3 etc numbers you keep referring to in the video as static pressure has nothing to do with static pressure. Those numbers represent friction rate. You're explaining how to use that duct slide completely wrong. SMH.

Terrible video more confused than I was before watching this video

Ok I don't have air returns in my 2nd floor rooms and I want to replace my supply ducts aswell so do I make the return and supply both 7 inch flex which is what is on the supply in 1 room now?

Hello David, what size main (incoming) flex should I use for a triangular terminal box that has 2 x 8" flex please

The regular guy has no other options but to do it themselves. The cost of living is out of control. You have to do it your self to survive. Thanks for sharing.

This is a lot of important info on supply theory! I haven’t seen anything like this elsewhere.

After watching this I opened the louvers in my return air vents & the system is probably moving 20% more air. I also removed every other fin from my living room registers to allow more air flow. And the sucking & whistling is gone from my return now. This is my third system in this house in 42 years. This is the first time I’ve had sufficient air flow from my AC. THANKS AGAIN!!

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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-iInIN89q8GU.html

I don't understand everything you said, but I understand a lot more than I did before. Thank you for taking the time to explain it to us. :)

hi I am A pastor I don't know nothing about air condition of building a home and right now I have all the walls done and they all remain only the 2 by force nothing no electrical done is work the plumbing is work and now I need to work in the air condition can you help me I have no clue about anything about her condition

Hi trying to fix a hot room , I changed the grill to same you showed , do I need to go from 5 to 6 flex in that room to cool it down more ? Is coming from a triangle at the end of the ductwork line box 2 5 inch line on each side to 4 vents 2 bedroom , small bathroom and one in dining room area , this one room is the one hot , no leaks

What does inside the duck work suppose look like from return vent to unit and from unit to one room as far material looking like inside of it and what point of 1500 soft house 500 is garage to have one big return vent and the other one e3 times smaller

I hate flex. Too much resistance to the inside material. Solid metal is best. HVAC is not something to cheap out on. It cost you in the long run.

what about the tonnage on air conditioner nice video will subscribe

... and if I'm not using flex?

How large of a return grill should you use for bedrooms? The return ducting is 9 inches

Great video, interesting information...Thank you. I have a question David, I want to replace my ductwork, located under the house, outdoor, on the ground, what type of flex is recommended? I live in Florida.

I haven't found anyone yet in my area who will do duct work modifications to our home. They are all happy to drop in a new HVAC but what we really need is to modify very badly remodeled ducts. One HVAC contractor even told me that he doesn't make enough profit doing ducts. At least he was honest. So if you are wondering why homeowners are watching your video, this could be why.

David, thanks for all the helpful videos. I have a 1600 sq.ft. older home and not an open floor plan. 3 ton heat pump with gas furnace. The main trunk line has 7 ea 6" flex lines and 1ea 12" flex line feeding a 2 trunk line about 20' away that has 5ea 6" flex . There is very little cfm at the end of 12" flex. Would a 12" inline duct fan work to boost cfm's for the 2nd box. The 2nd box jas plenty of cool air. Thanks for any help.

Thank you David your a good person and you definitely know your trade. I appreciate all your videos and all the knowledge your giving us. Hope all is well stay safe be well David

If I have a room 13x11 And I have a 6" supply grill Will be good to put a 6" return grill Above the door or will be better an 8" I remember when I start working on hvac we used 6" returns But now days I haven't seen that Anymore I see 8" returns even when the rooms has a 6" supply Wondering why?

David we have a house without ductwork and a finished basement we are wanting to put in a furnace and central air would it be advisable to try to service the first floor with ductwork in the ceiling otherwise we've been told we'll have to gut the basement

Thanks for the video. Especially that part about grills is super helpful for my situation

Flex duct should be outlawed, other than for terminations. It should never be used under a house. Rats love to chew right through it. Use alumaflex at the very least.

we are not going to run bedroom returns. 5-ton run 2 returns. all others run 1 return

Why .4? Every video i watch they always say .1 or .5 or something. They never EVER EVER explain what that .4 is and WHY they are using it and HOW to know what number to use. It's like telling someone, make sure your saturation temperature on your suction is 40°. If I've never learned anything about air conditioning then I want to know why 40°. You can't just throw out a number and move on. Please explain why you're using .4 and does that change in every application? How do I know when I'm supposed to use .4 or some other number?

Great video! Where can I get the wide spaced louvered registers and returns? The brick n mortars don’t appear to carry them. Thanks!

I have a 2.5 ton system in a 870 sqft house. 3 of the registers are ok. but 1 of the registers are noisy closest to the supply. and 2 of the registers don't get much air flow and the air is much warmer than the other 3. all on 6in. flex duct. i'm not sure about the size of the return. duct but the grille is 14x24 (what are your problems with this?) 1950's house with no insulation. im assuming thats why the tonnage is so high for the house size.

I have a new appreciation for HVAC guys!

Where flex legal anymore? Per hvac license

Very good, easy to understand Dave. I appreciate your instruction manner - not over my head with big terminologies!

David my wife and I appreciate your information its very helpful and huge money saver thxs for putting it all together

Thank u sir for the video. I am very hand and repair homes for a living. I am needing a ductwork designed for my home. But don’t want to pay an arm and leg. I will hire a professional to hook up the new unit. I want it efficient and have questions about how many returns the house needs. It used to be one. Now concensus seems to be some kinda return in each room or a vent pass through. I’m confused. Could you help me? Thanks -Jerry

Dude, don't tell homeowners how to do it. Then when they fuck it up someone has to go fix it. For runs off the trunkline, a 6 inch flex is sufficient for every single run in the house. I've seen runs where guys think too hard and put a seven inch for a room, a six inch, and eight inch for another room, etc.. No. Bedrooms, 2 six inch runs. Bathroom, one six inch. Living room, 2 or 3 six inch. Kitchen, one or two 6 inch. You don't need that duculator shit until you get to commercial. Then it really helps with a trunkline. You still gotta reduce it down the line.

You're definitely 👍 💯 right ✅, exelent job 👏 keep up the good work. I like how you explained basic things to upgrade the performance of the Hvac equipment and get the most efficiency and extend the durability, save money on service calls, simple things go a long way awesome work;)

Rob B 1 day ago Great videos! Thanks for sharing! Question, I have uninsulated air flexible connectors ducts for AC/Heat going about 15 ' to a retune and want to insulate them after they were installed. What is the best product or way to go about that - that you recommend? They have no insulation and I can tell they are losing hot air. Thanks!

i got a 4ton for 1300sqft thats 350ft per ton in southern Nevada easy 115 degree days, i aim to get 1600cfm and my filter is 20x20x1 side by side for a total of 20x40 filter return. i currently use the honeywell HD merv 11 filters but i think ill start using the 3m 1200 merv 11 because of the more surface area on the filter to help decrease static pressure if that doesnt help ill try to use 4in filter

Wish you were in Philly. We have a gutted 2 story row house 820 sq ft. My contractor who doesn’t know HVAC says he can do the job with flex duct. But I don’t like the design he came up with.

At the end of the video you said a woman had to turn her thermostat down to 74 and you change the grills and she was able to turn it back to 78 degrees. That's good that those grills improved her airflow that well she must have really had some serious issues, but In no way shape or form is 78 degrees cool in any house. Maybe for an old lady that's in her 80s. I have an 18 seer 3 ton 2 stage condenser that pulls humidity out tremendously well. My thermostat stays at 72 with around 46% humidity in my house in July and August. That's doing the job rather well and it's comfortable for me. If I set it at 74 / 75 with my condenser would be a little higher energy saving and more comfortable for most everyone else such as guest. 78 degrees and up on a thermostat is just not comfortable cool in a home and would only be for an old woman with poor circulation. My grandma is 82 years old and likes it at 78 to 80 degrees in her house in the summertime.

I have a 8*14 room what size duct for supply and return

There is a reason installers used to install a trunk which reduces as it gets longer, six inch runs were placed around the exterior walls so as the air blew down, it pushed all the unwanted temperature to the return, and the returns were slightly larger than the largest supply duct. The six inch runs blew even air and when yu needed more temperature for a larger room, you added another six inch vent. Why? Do you want to push more air out of one vent or push more air out of another spot in the room. In a car, they add vents for even cooling. Nowadays, I've seen so much bull shit in hvac systems its not even funny. I'll say this, go ahead and save the three or four grand on a install and go with the cheap bidder. That is gona be the guy trying to make money and he doesn't give one fuck about yur energy bill or when you will be ripping out walls and ceilings to replace duct. You will pay that money yu saved in the long run. Believe me, yu will wind up paying more on yur energy bill and you will replace all that flex one day. And if its behind walls, yull never know what has happened and you will be ripping out shetrock, hiring a painter, tearing yur home apart, etc.. if ya aint got the money to install a good system, buy window units until you do.

The ATCO flex duct calculator is not accurate as it more closely reflects metal duct values. Focus on velocity. 400 fpm on return and 600 fpm on branch supply ducts Vs static pressure. Manual D even states to use velocity over static. The ADI duct calculator is the one to use.

how marketable is this course

Hack 101

Thanks for the videos. Why do you read 0.1 friction loss? and then you used 0.4..... why based on what?

In Orlando Florida what R value should I have for flex?

what size melt main duct for a 2.5 ton 1200 square feet house for both sides on a package unit heat pump??

Set that duct sizing calculator on fire and do a manual j and d! These are our professionals. We’re f’d

Rule # 1. Dont educate the customer. If you are stupid enough to brake this rule, your phone will stop ringing or the phone of another tradesman.

Can i ask u a question couse here in florida no body can give me a answer why i have some two room that is always hot

I worked for a compnay and we'd fabricate our own attic boxes, lined on the inside for quietness AND insulated on the outside. Pain in the ass, but the customer got the best. Why don't you tell the customer that the units manual tells you how big the return duct has to be, along with the size of the supply duct. Tell em dude.

Really confusing. Lots of babbling and jumping around

What is your take on concealed ducted mini-split systems. Is sizing the same as a FAU? How about installing the unit in a vented crawl space.

Great video!

David I’m glad you mentioned about the return vents and sizes!! I just couldn’t understand why we have 2 (3) ton units in a 2 story house but our bedroom that is on the first floor is notorious hot all the time. Now that you mentioned the vents ours seem tiny!! I will go buy some new bigger ones!! I had been up to the attic and believed that maybe some of the ducts weren’t on or where loose but everything was fine. Thank you for that information!

Forgot to get to the tonnage

Hey David, Thanks for the video and your time. Quick question if I change my 16 Sears A/C UNIT to a 20 Sears do I need to change my ductwork?

David your videos are the best I've seen in terms of information and advise they are great. Thank Q!

hi david thanks for you videos .... how do u know wich friction loss to use per duct?

Thank you very informative, can you tell me if it matters where the heat outlet is placed in the room for best results mine seem to be to close to the room doors

hey day what do you think of heil. and I have an old house shopping around for contractors what to put it in the basement many folks just don't want to do it they want to go in the attic

I've always come here to this channel for the right info and right to the point.

What size would the main trunk be coming off the unit. I have 1000 sf basement and 1200 upstairs my unit is in the basement ? Thnks

David when using 8 in flex duct connected to a 8 in adjustable elbow do you pull the flex duct insulation over the elbow to insulate elbow or use separate insulation to wrap flexible elbow thanks please show video

Those don't look durable at all I have those in my home and they have holes.

Well hey david if we using .5 for the flex supply. What should the static pressure be for the return if its flex as well on the metal ductulator i dnt have flex ductulator

Great info! Thank you!

You are a fantastic instructor. Thank you for all the great information.

A lot of questions in the comments but no answers from no body, to bad.

Mr. Jones you are a HVAC genius. I am one to try doing stuff myself because I can never afford a to hire someone. Well we are building a small rancher in WV. after getting sick from west Nile virus I had to go out from work. My current home we are gonna rent out because I honestly cant afford to live in it anymore. It is gonna take awhile to do but Im trying to do most myself. We just had it framed so its wide open. The plan is to begin framing the interior and start roughing it in electric plumbing and hvac. I prey after watching your videos I can mange to do my own ductwork. Its a 32X44 rancher and I want to run flex line . I did a layout on my laptop and have the location for the furnace . Do you think there is anyplace I could go and they could tell me what I would need in regards to the sizing of material needed Flex Line Returns etc.if I were to buy from them.? Im not sure if any place would do that.The tool you used was very informative but I have never used one before so there is alot of learning. In the meantime Im going to look for more of your videos . Thanks you

Excelente!

David, what is your opinion about the SUPERCOOL SLIDE RULE if you ever used it? Really good video

Seems to me like they would make some metal ducts with flex ends on them. to reduce friction but somewhat keep the flex property. sure you can do this yourself. but they should sale some already made up.

Nice to have someone like you explaining this stuff.

This RU-vid video which you made is VERY HELPFUL! I am going to replace my grills, and my cousin who has found that her return ducting has holes in it is reading your video as I am typing as she just got a new 3 ton AC/HEAT HVAC unit and found that the AC doesn't blow hard enough to cool her mobile home. She guessed when she looked down her vent that the reason is that the reason is the holes in the ducting. Thank you for this video.

Hi David, Great video! We had an Aprilaire humidifier over our heater. It was on one side of rectangular insulation. We removed this humidifier because of moldy smell. We cleaned well and covered the hole temporarily. Smell is gone! But, now I need to get the house appraised and I want the patchwork to look more professional. The hole is about 18” x12” What is the best material to patch it? Thanks for your help!

Great video, thank you Mr Jones

if only everyone was this good at there job we be good

what is the name of that flexible duct calculator and where can I purchase one? Thanks

how many tons used that 6 duct pls

Great info. Thank you😊