How to Quickly Size Ductwork!

Explaining what is an air duct calculator, how to size of ductwork for an area as General rule: use 1 CFM per square ft. this will help on deciding how much air conditioning goes into any room.
Thanks for watching!
- David
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[@chancecooper4006]

Best and most simplest way that Ive seen someone explain the ductulater on here so far. Im a new subscriber!

[@thomaspierce9458]

Best and simplest... or Best and most simple... (Not "Best and most simplest...")

[@robmartin9735]

best overall presentation i've seen yetthanks David.well done!

[@acechoice45]

great Video Ive been in the trade for 4 years ur videos help me alot Thanks

[@hvactecster79]

Great video and tutorial David !! Take care, Brett

[@jonesacnaples]

Thank you, I hope it help you to understand return grill sizing better.

[@jonesacnaples]

I will try this week. Thanks for the idea.

[@AustinTXRealEstatebyFelix]

Great Explanation. Thank you for being a Teacher!

[@vemlacduong1954]

Thanks . This instruction open my mind.

[@aaronshensky9385]

Thank you David Jones

[@MujahidAli-yy8ti]

Thanks a lot & good advice

[@shahbaz66789]

very helpful sir, thank you

[@melvinbatista1374]

Great video very helpful.

[@jonesacnaples]

Thanks, I appreciate that comment.

[@eagletek1]

thanks for your wisdom

[@Gabriel-vz7ml]

Thank you David

[@jerrybinkley1737]

my name is Jerry I'm in Ohio I watched several of mr. Jones videos I even called him and he answered his phone and he was a great help to me this guy is a godsend thank you for your efforts mr. Jones Jerry Binkley Springfield Ohio

[@kimmikita1277]

Thank you!

[@hvacguy11]

This guys a beast dude

[@lio2137]

It's good my friend good job

[@JuanGonzalez-bn2ez]

Great videos

[@jonesacnaples]

Yes, need to know the rated capacity of your system. Blower CFM is your starting point.

[@juanmartinez-eh6ef]

👍🏼👌🏼 I like your explenation

[@jeffreywang6547]

Shared, subscribed.

[@quickfrostquickfrost1901]

thank you sir

[@jonesacnaples]

Thanks

[@cubanito725]

Good job.!!!!!!

[@dagestanifive]

Thank you man, that was a very simple explanation. I am going to take my contractors test soon and you explained how to use the ducculator wonderfully

[@jonesacnaples]

Glad it was helpful!

[@TheAdrian012275]

thanks Dave

[@jonesacnaples]

Yes, start with the air handler opening, then use the correct static pressure. .1 on supply and .05 on return. I am here if you need me. David

[@jrm3401]

Great video for the younger generations!!! Anyone looking to get into the business watch this video!!! I actually use .97 cfm/ per foot... More than one way to skin a cat!!!!

[@tonybaker1247]

You need to take the ACCA manual J 8 and D classes to learn how to do it the correct way.

[@josecarlosharojauregui3571]

Very good

[@jonesacnaples]

I would recommend you add a branch line,

[@baileysair]

David, very informative video..but you have the design friction loss wrong. Yes we design for half inch. That is what almost all residential units are built to. But you need to subtract component losses to get your AVAILABLE static pressure to size the ducts correctly. You have to subtract, registers, dampers, coils, filters and such then use that number for your friction loss which is always less than .5 and will result in larger ducts needed to deliver the proper amount of air. At our company we do not use rule of thumb to calculate air delivery. We do a complete manual J with room to room load analysis and size the ducts to accommodate the actual load which can vary greatly from the rule of thumb.

[@kathypinner432]

love your videos on a/c system. It is hard to get anyone to size the my a/c unit. I live in New Orleans, la. My house plans show 1725 sf living area including exterior wall. W/o exterior walls I measured the interior 1600 sf,. W/o interior walls measuring room I meausre apprx 1520 sf not counting interior walls. 3 BR, 2 bath house, insulated walls and attic, have a den, living room and kitchen (2 large windows face west living room and 1 small window face east bathroom) t). Contractors stated I need a 4 tons unit. Seem large. I had a 3 1/2 ton but return was smaller then recommended by your videos 20 X 24 or 25". Would it be a problem going with the 4 ton with a 24" x 24" grill.

[@JDB5824RG]

most 12x12 grills for example are actually 10x10 and .1 is OK for supply but .08 is better - also should mention the importance of not only sizing but how to maintain static and velocity also long runs.

[@rodgraff1782]

I believe the Trane duct calculator you were using is for ridged duct, not flex. They make a duct calculator for flex duct. Flex duct does not have the capacity of smooth ridged duct. We always sized residential ductwork for .08 static.

[@aminkhan-hv9nv]

Hey David. Would you use the same method for sizing the return duct and supply trunk. Flex duct. For 1400 sq ft home

[@JilkyInc]

Do a video about static pressures please

[@ImamguliyevK]

Should I add something for the winter time? I'm from VA and the winter here is quite cold.

[@jonesacnaples]

You should not install any duct work within the 1st 4 foot of plenum. Hope this helped.

[@guadalupejog]

Hello David, excuse my ignorance I have a question, your chart says " duct calculator" the new ones in the market says "ductulator" . Both charts are the same?

[@eagletek1]

How do size the main trunk coming off the unit on the supply? Do you use the information on the equipment ?

[@hvacrickone]

Cool!!!

[@josecarlosharojauregui3571]

Donde podre conseguir un ductulador, daludos sr. David jones

[@MrOlid84]

Hi. My name is Miguel. I'm having trouble working on sizing up the rooms in the home. I'm taking HVAC Course at UEI graduating this June. I'm just confused from when all rooms and you get the Return duct diameter how or which sizes do you start off to do your runs? I'd gladly appreciate to get your help with what sizes you start off with from your Return.

[@mercpusateri3321]

I'm finishing a big area in my basement, 900 sq ft. can I put the grills right in the main trunkline or should I branch off.

[@shabeelaa]

Sir which ac is good when 93 t load is needed chiller or package units. Am new to this topic

[@sammarchetti2484]

I think I can clear this up for everyone. If you need to deliver 800 cfm, select a fan that can deliver it at .7 or .8, instead of .5, then you have some available external static pressure to design your duct system with. A coil, filter,grill ,register,and damper use up .5 ex. S.p. Bottom line, if you have a 2 ton a.c., you will need a 3 ton blower. Unless you duct system just a couple of feet long.

[@jonesacnaples]

The first supply should not be within the first 4 foot, start reducing about every 400 cfm of supply drop to keep good static pressure.

[@Aubrey-is-loved]

I am new to sizing duct work and have studied Manual D in depth but have not yet been able to put into practice. I am curious why you are using a rule of thumb calculation for the avaliable static pressure and not using manual D calculations instead? Especially, why are you not using the Friction Rate Worksheet to determine static pressure based on a given blowers design value?

[@HeatGeek1]

MisterCristor man, what joke! the new guy gets it but The guy teaching doesn't. This is why 80%+ of all installs are screwed up. Keep reading and studying cristor. I encourage you to join HVAC TALK as a pro member.

[@mercpusateri3321]

would placing the vents (2 or 3 of them) directly in the the main trunk line vice branching off negatively affect the flow or efficiency

[@rustyshackleford3647]

No.. not if the system is sized to accommodate them... the lack of the branch lines means less pressure/temp loss

[@saljudeh]

Thank you, I wonder if you would help if I call

[@Jimhavasu]

David who ever taught you to use .1 friction rate on all supply ducts knows nothing about manual D or a how to use ductulator, not to mention the ductulator you using is for galvanized non lined duct, not flex duct. I might also mention using 1 cfm per square foot of conditioned space would indicate that you size by 400 square feet per ton, in most cases that would cause extreme over sizing! All sizing should be done by manual D's sister Manual J.

[@rustyshackleford3647]

THANK YOU... I'm a contractor in Charlotte... this is why people think we overcharge.. more to it than rules of thumb, but that can get you by if that's how you want to roll.. drives my stock up! lol

[@scottmuller8822]

Nonsense! I have done hundreds of duct designs using .05 Return and .1 supply and have never had a high static issue. Some newer systems that communicate and achieve 17 seer and beyond I will use .04 return. Good video Mr. Jones

[@tonylock68]

david after how many feet should I reduce down square duct main supply

[@rustyshackleford3647]

It's not how many feet, friction rate is based on per 100 ft... it's about CFM available.. as runs are installed, you can reduce trunk size to cover however many are left, keeping them straight and short as possible

[@fromra8569]

What you want to avoid is to size half the residence to 1.0 inches wc, and the other half to .07, cos if you do that youll end up with a cold side of the house and a warm side of the house... and aalways size your heat load to your AC needs,, unless you live in alaska,,

[@joeperez4651]

Lo Mar ;(())))

[@abdulkhuddus06]

Dear, Sir can explain me how to take duct size....example i have 1000 cfm, so.??

[@rustyshackleford3647]

need a ductulator..

[@hoozdis]

Your approach isnt even close to the Manual D methods

[@jkokuna808]

knowing what your blower is rated for is where you should start your duct sizing.

[@rustyshackleford3647]

That's putting the cart before the horse. You design the duct before selecting the equipment needed. Load calculations, duct design, then equipment selection.

[@jkokuna808]

@ Doug ummm, how about no! Load Calcs, Equipment selection (blower performance) then duct design. How do you know what your sizing to without knowing the blower performance? or where the operating point falls on the fan curve vs required CFM? Are you designing equipment for your duct size? or duct for your equipment? go look up manual J, S, & D! Sure there are a lot of "rule of thumb" tricks that will work for simple cooling/heating systems with no design expectations, those would probably be more specific to localized regions, that'll get you ball park with experience. blower data, ESP @ required CFM, pressure drops accross air devices, available SP, TEL, then you can determine friction rate. You cant put the cart before the horse, hahahaha, right back at you

[@rustyshackleford3647]

Blower size is dictated by CFM requirement which is dictated by the distribution system (duct) required to deliver proper capacity (load calculation). Otherwise you could have a 2000 CFM blower on an 800 CFM duct system.

[@rustyshackleford3647]

Using .1 friction is a rule of thumb. You should calculate your pressure drops, multiply by 100 then divide by total effective length. Now you have your friction rate to take to your duct wheel to DESIGN YOUR DUCT. How would you have a blower before that?

[@jkokuna808]

type of distribution system does not dictate CFM requirement. distribuition system is more or less determined by your construction limitations. more important... how do you know if you have enough static to overcome your pressure drops accross fittings, filters, dampers, and registers if you dont know what your fan is capable of putting out? do you have enough static left over to achieve desired room stratisfication? or throw pattern? Your only thinking in terms of CFM and not static pressure. Seriously though ACCA Manual D, Section 3-2 is a good place to start. you can even google it or better yet I quoted a paragraph from the first thing that popped up; "Once the Manual J room details and Manual S equipment sizing have been completed, we can begin to design the duct system for your project. If the duct system is not properly sized, the air conditioning system will most likely not perform as well as it should, have rooms that are too hot or to cold, excessive wear and tear on the HVAC system while costing more to operate. It is important to have the equipment selection made prior to performing the Manual D calculations because each manufacturer’s equipment is different which can impact the supply and return duct work size." -acsupplytexas

[@armandom.5299]

"im not sure i like that"

[@stevejollimore186]

Did you miss the text on the ductulator that says "friction per hundred feet"? You are missing the step where you determine the equivalent lengths of fittings and calculate friction rate PER hundred feet. I would also like to point out that you are sizing flex with a rigid duct sizing tool. Flex duct has a minimum two feet of effective length per foot. You are teaching people to use a rigid duct sizing tool for flex with no concern about the effective length of the duct. A static pressure of 0.1 is good, but a friction rate of .1 PER hundred feet is likely not correct. You need to take the Static pressure (0.10 ) and multiply it by 100, then divide by the effective length of duct from the air moving device to the diffuser. Count your measured length as two feet for every foot. On the back of your ductulator there are equivalent lengths of fittings.

[@jordanfaltysek9957]

I hope people still aren't doing like this. Your friction loss is not a set number. It's the starting static you get from the blower performance chart minus airside pressure drops divided by total equivalent duct length. It will not be the same for every system you do. Please buy a Manual D

[@pelonmoran3]

Shit i need to go back to tech school ,, i though i knew something did 8 service calls today one low on r22 ,3 bad capacitors 2 blower fans 2 thermostats, ,

[@lendssadiasa4814]

How can you i dentify the rectangular fuct size by just givin cfm? Tnx

[@deluxairhead]

Internal measurement should be used, not internal please ; }

[@fromra8569]

You are all drowning in a cup of water my friends. Hvac duct sizings is not rocket science. Every successful tin knocking installer out there will size a homes heat load to the locality,, its either arizona or minessota? supply duct sized to 1 inch water column is ok so long you design the whole house to 1 inch, , it will just be a bit noisier,, return design to .07 is more than enough. And for residential stop sweating the details... if you have a run longer than 100 feet , maybe you need two heating systems. Ive sized duct for over 10 years,,, and rules of thumb for your region is all you need, cos only you knows what works for your paarticular region, arizona or mineasotta

[@HeatGeek1]

Lo Mar Rocket science? no. Science? YES!!! Stop mixing up friction rate and static pressure please. Go back to school if this is unclear. the same goes the the OP. Disseminating incorrect information to the public diminishes my profession.

[@rustyshackleford3647]

Amen, brother.... has anyone even mentioned the lack of a load calculation? How many exterior walls to that room? What is the R value above, below and through walls and windows? Latent vs. sensible? We work hard for our licenses for a reason.

[@rodgraff1782]

Design the whole house for 1”? Most residential furnaces are only rated for .5” total.

[@fromra8569]

@@rodgraff1782 bull shit,, modern air handlers can really push air,, I’ve measured tons of systems out there and a good inch is fine. Seen done it

[@rodgraff1782]

@@fromra8569 No reason to get upset. I’m not talking about commercial systems, I’m talking about small residential furnaces. You can go up to what ever it says on the data plate. If what you are allowed, for the equipment you are working on is more, that’s fine. Most residential furnaces, in my time, had a rated total static pressure not to exceed .5 low side probe measured at a tapped hole on the blower door, and the high probe at the discharge plenum, before any cooling coils. I was a certified Testing and air balancing, Instructor, so I do know a little bit. Maybe you are talking about a large variable air volume systems, which run at several inches static pressure. Most residential furnaces I worked on that were running in excess of their rated total static pressure were not able to produce their rated CFM, and were running beyond their designed temperature rise, which is also specified on the furnace data plate. I am sorry if this is all BS to you.

[@biblebloopers946]

You use .1 static. Others use .05. Some use .08 Any of these will dramatically change the size of the duct. Who the hell is correct? Why do you just tell us what you use and not explain why you use it? I'm tired of these videos where they don't explain shit

[@armandom.5299]

"im not sure i like that"