Quick and Easy Duct Design Information
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- Опубликовано: 16 фев 2017
- Duct design is a very popular topic in our industry that does not get covered often, a lot of people are confused on what ductwork to use on what area. They do not understand that if the static pressure is too low you will hear it blowing too hard, or sucking in too hard, this could mean that the system is in pain and could shorten the life of the equipment and can cause high head pressure on the compressor, over heated coils and frosted copper lines if the system is undersized. Other issues that could happen are lower efficiency, high energy bills and shortened life of the equipment. The different flex diameters include flexible ductwork from a range of 4” up to 20” and there are many manufactures, Hart and Cooley, Thermaflex, Goodman Flex, Thermafoil, Flex Master, and Ultra Duct just to name a few. We recommend using the aluminum foil flex because of its durability and longevity. No matter how well you design a duct system the return and supply grills have to be able to deliver the air to the conditioned space, if you have supply or return grills that are 3/8” or less they need to be replaced to a minimum of ½” width in order for the system to breathe properly. The bottom line is the ductwork should not be too small and the grills shouldn’t be either to achieve the maximum efficiency the system is able of providing.
Thanks for watching!
- David
David@DavidJonesAC.com
Follow me on Facebook: / david-jones-ac-1010702...
Finally... a contractor that is not arrogant & will share some great info on common HVAC problems. THANKS!!
Thank you for watching I’m only here to help
*Easy to assemble **Fastly.Cool*
Nice to have someone like you explaining this stuff.
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’m glad the information helped thanks for watching
David, you did a great job explaining some complex details and giving valuable information in this video.
Excellent video!! We were going to replace ductwork ourselves. Now, we will get an HVAC person. Thx so much
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. :)
David my wife and I appreciate your information its very helpful and huge money saver thxs for putting it all together
Loved the information on wider grill spacing, that hasn’t even occurred to me. Thanks for the eye opener
This is a lot of important info on supply theory! I haven’t seen anything like this elsewhere.
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
I've always come here to this channel for the right info and right to the point.
This RUclips 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.
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
Thanks for the video. Especially that part about grills is super helpful for my situation
Very good, easy to understand Dave. I appreciate your instruction manner - not over my head with big terminologies!
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!
David - well I ended up purchasing a couple of frost king air diverters so far it seems a whole lot better than it was. I got the biggest ones from Home Depot. Our sizes is 8 x 14 but vents are directed in every direction. So directing them over the sleeping area is better. I’ll see how it goes
Well done. Easy to understand and nailed the return issue.- Thanks!
You are very good at explaining , Unrestricted
Airflow.
RETURN
THAT AIR !
David your videos are the best I've seen in terms of information and advise they are great. Thank Q!
Very informative. You are a good teacher! Thank you 🙏
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.
This video helped, thanks!
Great video, thank you Mr Jones
I have a new appreciation for HVAC guys!
Great info! Thank you!
Great info. Thank you😊
You are a fantastic instructor. Thank you for all the great information.
I appreciate that!
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.
Great practical real world situations you see as a "Seasoned Professional Technician". Great videos for the guys David. Thanks!
Great job on the video. Very thankful for you to post this. Question. How do you calculate splits on supply ducts? And whats the difference metal vs triangle duct-board wyes?
Return grills, versus pass through grills, when and where to use them when and not to use them???
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!
A great video, thanks for sharing. Would you know of someone in the Hobe Sound/Stuart area that has the same expertise as you? It is only a 2000 sf house but it is miserable to try to cool it and I know ducting is 80% of the issue.
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;)
Thank you for the comment
I appreciate you watching I’m only here to help
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
great info thanks
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.
k.scott phillips where do you live ?
Great video! Where can I get the wide spaced louvered registers and returns? The brick n mortars don’t appear to carry them. Thanks!
Very helpful for me considering replacing my ductwork along with the new heat pump we're planning. This man is passionate about his ducting!
Dude, get a metal shop to make your ductwork. I was a duct guy for a very reputable company which had a small tiny metal shop. We ripped out flex systems, ductboard systems that a mouse chewed into and died, and re did shabby ass installs. If yu go round pipe and flex runs, use six inch runs to each vent. Use reducers as yu go down the trunk. Make the return slightly bigger than the largest supply duct. And if yu use round pipe, get metal fittings made and use curved fittings to get to transition to the round pipe. It makes a difference. I fixed a job, I literally saw how much of a difference curves make vs. Flat square boxes and flat squares where the air changes direction. It makes a huge difference which translates into your energy bill which could turn into thousands and thousands of dollars
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.
KEITHS AC thanks! So if you figure all pressure drops of everything outside of AHU it should equal the TESP of unit?
Also why some use .1 for return and supply and others do .5 for return and
.1 for supply.
Too many contradictions
amazing thank you so much
i'm looking for any information on maintaining static pressure on my trunk as i take off runs seems crazy to reduce after every run
Hi David, I was wondering if you could help me size my addition . I want to use a roof top unit but seeting on the side instead of on the roof. Please let me know. I can give you more details if you do have time to help me out . Thank you for the info you provided on this great video.
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
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?
thank you so much
Great information thank you.
Good job Mr. Jones
LOL, "Ductulator" @3:00 . Great video, tks sir
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
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?
Pastor David Cruz no the ductwork has nothing to do with your furnace efficiency. Ur duct size will determine how many cfm you can deliver to your room.
Hey can you do a video on sizing cans and grills? 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
David, what is your opinion about the SUPERCOOL SLIDE RULE if you ever used it?
Really good video
not really, as long as ACCA approved I am sure it will be ok
hi david thanks for you videos .... how do u know wich friction loss to use per duct?
if only everyone was this good at there job we be good
Great video!
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
what size melt main duct for a 2.5 ton 1200 square feet house for both sides on a package unit heat pump??
18 by 10 splitting into 12 by 10 each way off the split , then reducing to ten by ten each way. Leaves plenty of airspace for 1000 cfms. Depends on the unit too. I've seen alot of chicken shit looking bowers with a frigging tiny tiny opening for the supply. We can thank the white collar world for that one, more engineering jobs had to be created for all the graduates, so God damn, common sense and what was a bit cheaper went out the window, and every thing went digital board and techie, which makes it cost way way more. I even saw an American standard unit with a chickenshit looking blower opening. So they're telling you to attach a duct four times the size of the blower opening. Bull shit. No techie fucker is gonna tell me it blows air thru that duct like an opening three times that size. The engineers probably cut costs to maximize profits there. So good luck in today's times of " fuck a good job and good work, I gotta make mine, and also the created engineer jobs where everything had to be revamped so newbie graduates have a white collar job". Oops, sorry for the rant. But things would be simple, men would take more pride n their work, etc. If uncle Sam ddnt have to create jobs for all the newborns because women gotta be a mom two three or four times.
Excelente!
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
Question, Should the supply air be in the ceiling? or below in the hall?
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.
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
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!
Good info, thanks.
Thanks for the videos. Why do you read 0.1 friction loss? and then you used 0.4..... why based on what?
Supply and return air uses different friction loss
Where can I get the wide openning supply grills some supplies only have the small .
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
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?
Love it love it
... and if I'm not using flex?
Great video
thank you hope it helps
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
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
Thanks Davis, you are very helpful and explain things in a very understandable way. Much appreciated!
You started to mention tonnage but then didnt. I am getting quotes now for a new 5 ton package unit and my returns total 612 sq in. Most companies have noted those need to be increased but none have mentioned the duct work they supply. There are two 12" flex duct and that just doesn't seem to be enough to me. Is it? and what size should it be? (Those two 12" ducts currently feed one box when then has a flex duct going to a small return in a nearby room) Thanks for the video and in advance for your reply!
adnedarn the
If you haven't yet, your going to want to Increase your return to 2 20 inch duct optimally. 2 12s is not nearly enough
Customers as well as companies tend to oversize. Are you SURE 5 tons is the proper size? What's the square footage, and what climate? To answer your question, 5 tons × 400 cfm = 2,000 cfm. At 2 cfm per square inch, that's 1,000 sq in. of filter area. So you need to increase at least 40%. As far as the duct, it depends on the length, and any bends, etc... but you are probably looking at two -14" as a minimum. I would do two - 16", and install dampers. FYI two - 14" doesn't sound like much of an increase, but it is. A 14" does 50% more than a 12". So swapping the two 12" for two 14" is the same as keeping the two 12" and adding a 3rd, 12".
Also, how small is the connecting return?
@@jakekeeton8332 Holy shit! TWO 20" returns? That's WAY too much!
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?
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.
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?
What's your opinion about whether a duct system can be OVERSIZED. Interested in hearing your take on this.
I have rarely seen a oversized duct system
if you have oversize supply duct system that should not be to much of a problem, especially if it's variable speed, may need to use balance dampers depends on tonnage
from my experience most of the time no problem, makes for better air, flow lowers energy usage
always use good supply grills, and return
thanks for watching
Slightly larger duct shouldnt be to much of a problem.... BUT ... if duct is GROSSLY oversized... it will greatly reduce air flow,satic pressure and diffuser throw...... and create an unhappy customer
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.
correct on the tonnage, sounds like it very ubdersized
put most of the air out furtherst from the return.
to get good even temp
thanks for watching
what about the tonnage on air conditioner nice video will subscribe
Great video. I have some specific questions on how to tie in two flex returns on a 3 ton gas pack. I have a 14"flex that was reduced to 12" in the duct box for some reason and a 10" flex return at another grill. Duct work was just redone. Is this sufficient in size? It comes off the unit with I believe a 16" roughly 6 feet then it "Y" 's to the 14 and 10 off that. Again that was on returns. Your help is greatly appreciated. Is that setup sufficient, besides possibly upsizing the flex returns. My grills are whisteling.
you will need to use reducers, go to HVAC supply house
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
yes if there is enough space
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.
How do you know the minimum trunk size you can use ?
best of luck
NICE
Is there a specific place to purchase the Ductulator you are using?
Is there a ever reason to not insulate flex ducting in between floors? Ive lived at my house in Virginia for 2 years. Its about 20 years old. I just discovered 2 sweat spots coming from uninsulated flex tubing in the downstairs ceiling. The HVAC system inside and out are 3 years old and in great shape. By cutting holes in several ceiling areas ive noticed that all of the duct work in the 1st floor ceiling is uninsulated while the unit in the attic is insulated and installed to a high quality.
Always use insulated flex duct... no exceptions.... all ductwork should be insulated!! Including return !! Some others will cut corners or tell ya the return duct doesn't need to be insulated...
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
An HVAC supply house isn't going to tell you how to size your duct system. You need a proper load calculation done on the house, which will size your system and ductwork based on square footage, windows, insulation, etc. I've been an HVAC installer for 15 years and it took me several years to be able to properly design a duct system. My advice to you is to hire a professional before you fuck it up, and I'm not trying to be rude, I'm just being honest with you.
what is the name of that flexible duct calculator and where can I purchase one? Thanks
thanks man
No problem!
Thank you
In this video, you are using .1static for supply and .4 for return. In another video, I believe, you were using .1 static for supply and .05 for your return. Can you explain the difference?
He was desizing to make up for friction loss
@Mike Taylor He was desizing for friction loss. In either this or that last video he says to NOT undersize the the duct. I can only assume by some transverse property that the desizing on the chart is equal to using a larger duct for the return.
Always upsize them Returns. David Knows...Get the Unrestricted AIR back to the System
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.
Hello David, what size main (incoming) flex should I use for a triangular terminal box that has 2 x 8" flex please
Were do you get the grills that you refer to in your video