Thanks for your comment, I have done this so many times that I have duct sizes memorize. The most important thing is not to undersize your duct system. The returns being the most important. Keep in touch my friend.
I can say, working in the field without using computer calculations, Mr Jones will get as close as humanly possible to get accurate on layouts... Thank you David!!!!
3 ton = 1200 CFM for a house with ducts for 1350cfm Great Job David over sizing duct makes for quite operation.... Smart, Real Smart,,,,,,, Thank You for the video,,,,,,
My God I thought I knew what I was doing cutting all these extra supply ducts into my ceilings and absolutely no return at all. No wonder I have 2 a/c units (4 ton and 3.5 ton) for a 5000 sq ft house and can't get the right temps going. THANK YOU SO MUCH. I can't wait to rip all this old ductwork out and start from scratch. I wish you were in Miami!
I do need to get a manual D, I know from many years or experience What I am showing will work. When you are actually in the field you have to know what will work and what will not. Thanks for watching.
I'm confused about something. If the 3-ton unit handles 1,200 cfm's how can you be okay with 1,350? I'm still in my hvac program in school and need to watch these videos and I like how you discuss the topics. Keep them comming I'm learning alot from people like you good sir.
Can you please elaborate more on placing the registers on the perimeter walls? I feel I need to understand this better. I'm designing a small office space and need to reconfigure the supply and return. Currently, the system has the return in the center of a perimeter wall and two 10x10 registers located closer to the center of the small 300ft2 space. I wanted to install the registers on the perimeter walls like you suggest and move the return away from the perimeter wall.
What I do is take the total CFM that the equipment is delivering, and divide it by the square footage of the home, to get the CFM per square foot. I size the duct for each room, per its square feet. Then work backwards to the trunk lines. I never used flex, and never used od ball duct sizes. If a 7” was calculated,I used an 8”. Screw that flex duct. That’s for weekend wannabe HVAC installers. Real HVAC installers use ridged pipe, externally wrapped with foil back insulation and vapor barrier. I’ve got no good use for soft flex duct. The only thing is good for is rats nests.
That was the best HVAC Duct video I have seen to date, easy to understand. Thanks... Only one more question what determines how much CFM needed per room? Do you have a video that shows that? New Subscriber...
What I don't understand is that for 1200 sqft a 2 ton system is recommended. But that only gives you 800 cfm and everything I read says you should have 1 cfm per square foot. How does this add up?
Ok so my room is 11×12sq ft. X .96= 126CFM that's the amount of cfm that I need for that room? So, I will be good with a 7 inch flex duct? If so how do you know what size supply register?
I have watch some of your videos and like them for the most part but I disagree with your 4" is useless comment. A 4" can carry roughly 35-75 cfm depending on static pressure as with variable speed blowers which would cover at least 35 sq ft. I have used 4" ducts for small rooms that have minimal heat load or outside walls for years with no complaints. Remember the rule of 1cfm/sq ft , 400 cfm/12000 btuh per ton cooling and 20,000 btuh for heating tonnage(it's easier to heat than to cool). And I also use a rule of thumb of 1-10" duct per ton and divided evenly. So 1-10" = 2-8"/10", 2-6"/8" , 2-4"/6" and likewise in reverse.
Good video my only concern is flexible duct. No good installer would ever use all flexible duct hard pipe is so much better airflow cleaner and easier on the equipment. If designed correctly you will not have excessive sound.
Mr. Jones, I love your videos. Would have enjoyed apprenticing under someone like yourself. In Canada, all of the duct systems must be designed by an engineer or someone with a stamp. The Canadian government moved legislation through last year destroying what a tradesman can design. This is what happens when you give men in suits-and-ties the power of deciding who is capable of designing mechanical systems. It all stems from a few bad apples making poor decisions in design, usually severely undersized.
Thank you teacher David How much can I charge for one house dimension 1200 square feet new duct work installation and new equipment?? Thank you and I’ll hope your answer Sincerely Manny
From my experience you can usually do 1 CFM per SQ foot of the room. This could change depending on the heat load of the room, like big glass doors etc or if the sun hits that glass all day. But generally you should be ok with 1 CFM per SQ foot.
HI David. I have been watching your videos and appreciate the content you put out on youtube. I live in California San diego. What's the code for condensate drains? What I'd the usual setup for primary drain and second drain for a attic horizontal install?
Liked your video, not sure I follow 100% because new to me, but leaned a lot watching your video. I paid $5000.00 2 years ago for a whole new duct system and still sucks. 4 bedrooms split plan. 3 bedrooms on one side of house with inside unit and hard blowing air while master bedroom on other side of house with little air flow. Got ripped off.
You calculated 1350 cfm needed but the system can only support 1200 cfm. How this is working? I am a noob. Just trying to understand. You mentioned it is because of noise reduction, so always our cfm should be lower than the ton system to avoid such noises?
He should have room size shown on the sketch. Looks like he could have upgraded to a 3 1/2 ton. Bathrooms can use a 6" instead of a 5" because of taking a hot shower and oversize the kitchen because of the cooking. Always make the return air as big as possible because the pleated filters WILL restrict air flow and when they are bigger you wont hear the air being sucked in. You can't make it too big. To see if that fancy filter you bought is restricting too much. (evaporator need to be clean)Turn the blower on, and remove the filter, go to the closest register from the supply, hold your hand right up to it, have someone put the filter back in, if you feel the air supply drop...then it is restricting too much. The unit doesn't care how big the supply is. only how much air is going across the evaporator. Always get an inspection access between furnace and the evaporator for cleaning and inspecting.
HELP PLEASE! Can you tell me the requirements of a vertical fan coil unit needed to heat vent and cool a level 4,292 cuft in size? (29L x 18.5W x 8H) This area contains a kitchen, bathroom, laundry room, living room and 2 bedrooms. Also can you tell me if any additional equipment would be required to work with the VFCU? My questions are based on the idea of renovating a 3 level house in a way that allows each level to be completely independent of each other, eliminating the need for a commonly shared furnace and hot water tank. Each level with the capacity to be isolated, will have its own electric water heater and VFCU, and the only common area will be a small room on the lowest level, housing the main shut-offs for water, gas and electricity.
Thanks for these videos. Question for you, I have a house that an addition was recently done. The original house has a 2 ton unit, and square feet for CFM is 889, so that leaves 89 CFM in addition. Now I’ve added 498 sqft. So at 1387 I would assume I need a 3 ton unit. My question is what point over the Ton=CFM would you need to go to the next size? I could add a closet vent or two if I need to be over for what a 3.5 ton unit would have enough flow. So if you have 300 CFM more, would you go bigger at that point? Thanks in advance
Typically you don’t want to exceed 2 ft./min. per square inch. For instance he was using .1 static pressure as his base. And he said he was using flex. He said .1 static pressure is 300 CFM‘s per a 9” run. But actually it would be 220 CFM‘s for flex. But let’s just go with 300. A 12 x 12 register is 144 in.² times two equals 288. So using a Ductulator when I look at 9 inch at .1 it’s 300 ft./min. So that would max out that grill any more cfms and that grill will be noisy.
Based on the size of the room he oversized the ductwork to make sure the furnace never starves for air. He installed ductwork that can handle 1350 CFM while the machine supplies 1200 CFM. This system should perform quietly.
You did not say how you selected the flexible brach sizes for each room. Also, flexible ducts are the worst enemy of air circulation. We in Canada never use them and never recommend them unless it's a cheap contractor who gets away with it.
Just finished doing a ducted ductless mini split diy with all 4in supply duct "pretty much useless" seems to be mostly accurate 🤦 so maybe im not so finished yet
@Simon TemplarI like how comments don't age well. The question wasn't answered, and my knowledge was off, maybe I was thinking FPS. To Luz L, who probably doesn't care anymore or has figured this out: CFM is just cubic feet per minute, and you can get 300 cfm just by having a blower rated to put that out from what is called a central air unit or handler. There will be branches or duct tied into that unit (unless it's ductless) that will distribute air throughout the ductwork, this is known as forced air. The only things that will effect the known or wanted cfm are: cleanliness, blower power, and length of ductwork as well as it's size (supply and return grills match duct size).
In my opinion, this is probably the worst video I've ever seen on duct sizing. If you don't mind, there are two things that I would like to point out here... First, you don't explain at all how you came up with your CFMs for each individual room, along with determining each room's duct size. All you did was assume that the viewers of this video already knew how to calculate all of that information. For example, how do you know that one room has a 12"x8" box/grill, the return grill is going to be 12"x12", etc?... Also, at 4:32, you said you don't use 4" flex because it's pretty much useless. I know several long-time, certified HVAC Technicians who use 4" flex in small rooms, such as bathrooms, etc, and those smaller rooms all receive the proper airflow after their rough-ins, trim-outs, etc are finished. One of them in particular has been this field for over 30yrs... From 4:40 - 5:00, you mentioned ADDING more CFMs in order to combat mold, mildew, etc in a walk-in closet. Did you know that, the lower the temperature within a conditioned space, the MORE humidity is added TO that space?... Yes sir, I learned that in school. If you don't believe me, try taking your psychrometer (if you have one) and measuring your relative humidity directly at the supply plenum, immediately where the ductwork comes off of the air handler or furnace (or just verify that fact by looking at a psychometric chart...) Now, I can understand providing proper airflow to a particular area within that conditioned space. And if that is what you are trying to achieve, (in my opinion), I would install a de-humidifier in the attic, and have a drop in that walk-in closet. THAT'S how you combat mold, mildew, etc... Other than that, I love your videos. I am a subscriber of your channel, and an avid viewer of all of your videos. I just wish your videos were a little more 'technical', or complicated. Other than that, keep up the good work.
Finally a video which answers questions and is not just a promotion for someone's business. Thank you for real world answers.
Thanks for your comment, I have done this so many times that I have duct sizes memorize. The most important thing is not to undersize your duct system. The returns being the most important. Keep in touch my friend.
I can say, working in the field without using computer calculations, Mr Jones will get as close as humanly possible to get accurate on layouts... Thank you David!!!!
Nice. Clear, concise, and, as promised, very real world.
3 ton = 1200 CFM for a house with ducts for 1350cfm Great Job David over sizing duct makes for quite operation.... Smart, Real Smart,,,,,,, Thank You for the video,,,,,,
thanks
My God I thought I knew what I was doing cutting all these extra supply ducts into my ceilings and absolutely no return at all. No wonder I have 2 a/c units (4 ton and 3.5 ton) for a 5000 sq ft house and can't get the right temps going. THANK YOU SO MUCH. I can't wait to rip all this old ductwork out and start from scratch. I wish you were in Miami!
The dudes ending just killed his entire video. He totally transposes his required cfm with the supply.
Thanks for the simple explanation of how to use ductulator.
I do need to get a manual D, I know from many years or experience
What I am showing will work. When you are actually in the field you have to know what will work and what will not.
Thanks for watching.
please tell me how to start in the field . im a mechanical engineering graduate
Find people in the field that willing to teach you the knowledge
how do you size the supplyl grills?
Nice clear data that will help me size new ducts
Awesome teaching buddy! I simply can't afford to have somebody else do it. I know how to listen and learn though! Thank you!
I'm confused about something. If the 3-ton unit handles 1,200 cfm's how can you be okay with 1,350? I'm still in my hvac program in school and need to watch these videos and I like how you discuss the topics. Keep them comming I'm learning alot from people like you good sir.
the 3 ton unit creates 1200 cfm. a 1350 cfm supply ductwork system can handle what a 3 ton unit is pushing out.
Great easy to understand explanations. Will share with team. Thanks for posting.
Good Stuff David. Thank you for sharing your experience and knowledge. Much appreciated.
Can you please elaborate more on placing the registers on the perimeter walls? I feel I need to understand this better. I'm designing a small office space and need to reconfigure the supply and return. Currently, the system has the return in the center of a perimeter wall and two 10x10 registers located closer to the center of the small 300ft2 space. I wanted to install the registers on the perimeter walls like you suggest and move the return away from the perimeter wall.
What I do is take the total CFM that the equipment is delivering, and divide it by the square footage of the home, to get the CFM per square foot. I size the duct for each room, per its square feet. Then work backwards to the trunk lines. I never used flex, and never used od ball duct sizes. If a 7” was calculated,I used an 8”. Screw that flex duct. That’s for weekend wannabe HVAC installers. Real HVAC installers use ridged pipe, externally wrapped with foil back insulation and vapor barrier. I’ve got no good use for soft flex duct. The only thing is good for is rats nests.
Very informative video ! I can tell you don't even have to think about it to calculate it. It's obvious this is not your first rodeo !
I will do a static pressure test, I promise. Thanks for watching.
Hey amigo if a room is 12x12 =144sqf how can I know what size of flex ducting should I used
Thank you! Really good advise and simple explanations
I am glad it helped...
The only thing you should have discussed is 400 cfm per ton, that's on a furnace ,we always calculated 425 per ton if you have a fan coil or heat pump
Would be perfect if we would know size of the house and rooms as well
Excellent video and thanks for sharing your knowledge.
Does it mean as long as the total return cfm is a little less than the cfm from the AC then the return air flow would be quiet?
Great video David
Please do the static pressure test when you get it running.Great video
Great videos. Love watching these.
That was the best HVAC Duct video I have seen to date, easy to understand. Thanks... Only one more question what determines how much CFM needed per room? Do you have a video that shows that? New Subscriber...
thank you for this video! very helpful. what about the main trunk line? is there a calculation for that?
Thanks I hope it helped, I am here to help.
Guy sure does know his stuff
Hello. Can you tell me if new flexible ductwork has a smell? I have allergies and am thinking of replacing the ducts after 19 years.
What I don't understand is that for 1200 sqft a 2 ton system is recommended. But that only gives you 800 cfm and everything I read says you should have 1 cfm per square foot. How does this add up?
I like this video. I learned a lot. Where can I get that air duct calculator?
very good video nice to share your hard earned knowledge!!!
Good lesson man thanks
Another great video.
Just use the multiplier of .96 over sq ft.. Example 100x.96= 96cfm
Or 6. " flex which equals 100 cfm
Ok so my room is 11×12sq ft. X .96= 126CFM that's the amount of cfm that I need for that room? So, I will be good with a 7 inch flex duct? If so how do you know what size supply register?
I have watch some of your videos and like them for the most part but I disagree with your 4" is useless comment. A 4" can carry roughly 35-75 cfm depending on static pressure as with variable speed blowers which would cover at least 35 sq ft. I have used 4" ducts for small rooms that have minimal heat load or outside walls for years with no complaints. Remember the rule of 1cfm/sq ft , 400 cfm/12000 btuh per ton cooling and 20,000 btuh for heating tonnage(it's easier to heat than to cool). And I also use a rule of thumb of 1-10" duct per ton and divided evenly. So 1-10" = 2-8"/10", 2-6"/8" , 2-4"/6" and likewise in reverse.
Robert L 4" flex is useless 4" hard pipe is fine
Dalton Morrison not true... if it’s not a long run thn 4 inch is fine but most people do seem to prefer 5” nowadays
Hello David, can you do a video on static pressure on a residential home.
Good video my only concern is flexible duct. No good installer would ever use all flexible duct hard pipe is so much better airflow cleaner and easier on the equipment. If designed correctly you will not have excessive sound.
Hey this is great thanks!
Mr. Jones, I love your videos. Would have enjoyed apprenticing under someone like yourself. In Canada, all of the duct systems must be designed by an engineer or someone with a stamp. The Canadian government moved legislation through last year destroying what a tradesman can design. This is what happens when you give men in suits-and-ties the power of deciding who is capable of designing mechanical systems. It all stems from a few bad apples making poor decisions in design, usually severely undersized.
Thank you teacher David
How much can I charge for one house dimension 1200 square feet new duct work installation and new equipment??
Thank you and I’ll hope your answer
Sincerely
Manny
Great video, thanks a lot, could you please tell me how to do air balancing??
3 ton = 1200 CFM for a house with ducts for 1350cfm?
Same Question
Great show, my son is thinking about changing out his ductwork. Built 1956 so it’s way out of date. Thanks 33771
What if you only have 1200cfm to play with and you install ducts for 1500 cfm
great job sir
hello its a good vedio ,we can learn lot of knowledge.
Annie C. Hi.
Great video!
David do I need a separate return in a room that is closed off from house and if so how big of return its about 250 sq feet
Ing. David jones saludos donde puedo conseguir un ductulador gratis
Nice job. My question how do you determine the amount of cfms in each room?. I just see you start from the vents and with good experience. Thanks.
From my experience you can usually do 1 CFM per SQ foot of the room. This could change depending on the heat load of the room, like big glass doors etc or if the sun hits that glass all day. But generally you should be ok with 1 CFM per SQ foot.
How many CFM will 10, 11, 12 inch duct allow?
Thanks
How many square feet have this house?
for this project what is the duct size for the 2 Returns
HI David. I have been watching your videos and appreciate the content you put out on youtube. I live in California San diego. What's the code for condensate drains? What I'd the usual setup for primary drain and second drain for a attic horizontal install?
hi david. what was the sqft of airconditioned space on this house
very very good
Liked your video, not sure I follow 100% because new to me, but leaned a lot watching your video. I paid $5000.00 2 years ago for a whole new duct system and still sucks. 4 bedrooms split plan. 3 bedrooms on one side of house with inside unit and hard blowing air while master bedroom on other side of house with little air flow. Got ripped off.
You calculated 1350 cfm needed but the system can only support 1200 cfm. How this is working? I am a noob. Just trying to understand.
You mentioned it is because of noise reduction, so always our cfm should be lower than the ton system to avoid such noises?
He should have room size shown on the sketch. Looks like he could have upgraded to a 3 1/2 ton. Bathrooms can use a 6" instead of a 5" because of taking a hot shower and oversize the kitchen because of the cooking. Always make the return air as big as possible because the pleated filters WILL restrict air flow and when they are bigger you wont hear the air being sucked in. You can't make it too big. To see if that fancy filter you bought is restricting too much. (evaporator need to be clean)Turn the blower on, and remove the filter, go to the closest register from the supply, hold your hand right up to it, have someone put the filter back in, if you feel the air supply drop...then it is restricting too much. The unit doesn't care how big the supply is. only how much air is going across the evaporator. Always get an inspection access between furnace and the evaporator for cleaning and inspecting.
Don't happen to live near Tucson Arizona? Need mobile home done for rental.
E Buzek. Thank you.
HELP PLEASE! Can you tell me the requirements of a vertical fan coil unit needed to heat vent and cool a level 4,292 cuft in size? (29L x 18.5W x 8H) This area contains a kitchen, bathroom, laundry room, living room and 2 bedrooms. Also can you tell me if any additional equipment would be required to work with the VFCU? My questions are based on the idea of renovating a 3 level house in a way that allows each level to be completely independent of each other, eliminating the need for a commonly shared furnace and hot water tank. Each level with the capacity to be isolated, will have its own electric water heater and VFCU, and the only common area will be a small room on the lowest level, housing the main shut-offs for water, gas and electricity.
how the hell can u fit a 2br suite into 29x19? Shit I'm compromising with the same rooms in a 27x34. Is it for little people or something?
Hi sir do you do hand on training? What is your fee?
How do you calculate the long metal supply trunk line with reducers? per a 3 ton unit
Hello sir. Are you still working in hvac industry? I would like to ask few questions regarding on ducting system if you dont mind.
Hello sir how can i start to design?
how come you use a 8'' duct for a 12x12 room and then a 9'' duct for the other room that's 12x12 ???
Pretty sure those are the grill size not room size
Thanks for these videos. Question for you, I have a house that an addition was recently done. The original house has a 2 ton unit, and square feet for CFM is 889, so that leaves 89 CFM in addition. Now I’ve added 498 sqft. So at 1387 I would assume I need a 3 ton unit. My question is what point over the Ton=CFM would you need to go to the next size? I could add a closet vent or two if I need to be over for what a 3.5 ton unit would have enough flow. So if you have 300 CFM more, would you go bigger at that point? Thanks in advance
Lla😊
like your vids. I'm in Texas, but I want to work for you!
Thanks great video! can you explain the 0.96 btu per sq ft.
How do you determine the grill size based on the duct size?
Typically you don’t want to exceed 2 ft./min. per square inch. For instance he was using .1 static pressure as his base. And he said he was using flex. He said .1 static pressure is 300 CFM‘s per a 9” run. But actually it would be 220 CFM‘s for flex. But let’s just go with 300. A 12 x 12 register is 144 in.² times two equals 288. So using a Ductulator when I look at 9 inch at .1 it’s 300 ft./min. So that would max out that grill any more cfms and that grill will be noisy.
Ser can you show me in a industrial plan i will Line to led more of this ac intalling
what a second here! You have a 3 ton that's 1200 cfm and you said you calculated needing 1350 and you are good???
you just undersized the system
no this works well
Based on the size of the room he oversized the ductwork to make sure the furnace never starves for air. He installed ductwork that can handle 1350 CFM while the machine supplies 1200 CFM. This system should perform quietly.
You did not say how you selected the flexible brach sizes for each room. Also, flexible ducts are the worst enemy of air circulation. We in Canada never use them and never recommend them unless it's a cheap contractor who gets away with it.
I Could really use some help on a church gym project, not sure if you are still around.
where are you
Iowa
Just finished doing a ducted ductless mini split diy with all 4in supply duct "pretty much useless" seems to be mostly accurate 🤦 so maybe im not so finished yet
Thanks for watching.
nice Video
please correct me how to decide the duct length.
Hi: Excuse me for this dumb question. How do you get 300CFM with a 9in flex (in the living room) ? Thank you
Luz L Must have more than 1 supply in that room. Not getting 300cfm out of 1, 9" flex.
@Simon TemplarI like how comments don't age well. The question wasn't answered, and my knowledge was off, maybe I was thinking FPS.
To Luz L, who probably doesn't care anymore or has figured this out: CFM is just cubic feet per minute, and you can get 300 cfm just by having a blower rated to put that out from what is called a central air unit or handler. There will be branches or duct tied into that unit (unless it's ductless) that will distribute air throughout the ductwork, this is known as forced air. The only things that will effect the known or wanted cfm are: cleanliness, blower power, and length of ductwork as well as it's size (supply and return grills match duct size).
@Simon Templar Some things to consider when changing ductwork: insulation, values, and size. More than often the return is undersized or too short.
5 Inches Air duct didn't exist anymore
In my opinion, this is probably the worst video I've ever seen on duct sizing.
If you don't mind, there are two things that I would like to point out here...
First, you don't explain at all how you came up with your CFMs for each individual room, along with determining each room's duct size. All you did was assume that the viewers of this video already knew how to calculate all of that information. For example, how do you know that one room has a 12"x8" box/grill, the return grill is going to be 12"x12", etc?...
Also, at 4:32, you said you don't use 4" flex because it's pretty much useless. I know several long-time, certified HVAC Technicians who use 4" flex in small rooms, such as bathrooms, etc, and those smaller rooms all receive the proper airflow after their rough-ins, trim-outs, etc are finished.
One of them in particular has been this field for over 30yrs...
From 4:40 - 5:00, you mentioned ADDING more CFMs in order to combat mold, mildew, etc in a walk-in closet. Did you know that, the lower the temperature within a conditioned space, the MORE humidity is added TO that space?...
Yes sir, I learned that in school.
If you don't believe me, try taking your psychrometer (if you have one) and measuring your relative humidity directly at the supply plenum, immediately where the ductwork comes off of the air handler or furnace (or just verify that fact by looking at a psychometric chart...)
Now, I can understand providing proper airflow to a particular area within that conditioned space. And if that is what you are trying to achieve, (in my opinion), I would install a de-humidifier in the attic, and have a drop in that walk-in closet.
THAT'S how you combat mold, mildew, etc...
Other than that, I love your videos. I am a subscriber of your channel, and an avid viewer of all of your videos.
I just wish your videos were a little more 'technical', or complicated.
Other than that, keep up the good work.
Hahahahahaha!!!!!
good luck finding odd sized flex. Ive seen some of the american way to install duct systems...all hacks!! Come to CANADA and learn the right way.