For those wondering about the ceiling affecting the CFM to each room: I think the ceilings where accounted for during the initial load calculation to size the equipment using Manual J. Since you have the proper number of tons from your system, then what he did was divide the total CFM output of the unit by the total square footage of the home so you end up with .788 Feet per minute. When you multiply that by the square footage of each room you get cubic feet per minute again.
Great video, it'll be a big help in my house design. I hate to be a stickler for details, but @1:17 your cfm calc is off on your 22x20 room. Should have been 352 and you have it at 76.8 (such as for your 8x12 room)
This is a brief tutorial and is not intended to be a solution for all duct sizing applications. If you are an architect or an engineer might I suggest that you properly perform load calculations and use the latest duct sizing software, but for everyone else in the world this duct sizing method will work in 95% of the applications. If you lack the common sense to know that a room with 12 foot ceilings will require more air than a room with 8 foot ceilings, I would suggest you find a different line of work.
Basic ok tool for the typical ranch or row house, but how about a more complex duct system? One should really use manual J to figure the load per room, and then manual D to size ducting. To use only .1 for supply friction is a bit misleading, I find quite a few of my installations have friction rates for supply ducting at more like .05. I am laying out a duct system tonight which as 460 equivalent feet of duct from the farthest return to the farthest supply. .1 is for 100 equivalent feet of duct not 460?
If celing heights vary wouldn't it be more accurate to calculate the cubic feet of each room and divide the cfm up proportional to the cubic feet rather than the square feet?
I think the ceilings were accounted for during the initial load calculation to size the equipment using Manual J. Since you have the proper number of tons from your system, then what he did was divide the total CFM output of the unit by the total square footage of the home so you end up with .788 Feet per minute. When you multiply that by the square footage of each room you get cubic feet per minute again.
First I’m just a home owner interested in learning ,I always thought there was a crazy math to figuring out the dimension of the and then the duct size ,with your book it’s not as hard as I once thought ,so thank for making that easier to understand for me , My question is just figure the area of the room doesn’t factor in how far away the room is from the unit , Now if the unit is (this my home)basementand the biggest room in the house are right above the unit on the 1st floor and by rule those rooms would have larger ducts then the smaller room above them , would most of the air pressure die off by the time it reached the 2nd and even more by the 3rd floor ,dose the length of the duct work not get factored in at , again I don’t install and I am only concluding on my experience, can any explain how I can check calculate my ducts to make sure the sizes are correct, thanks again I will continue learning more to be an educated consumer
Hi, I am in trade school now. For rooms that are farther away, the trunk line (the main line spanning the house) will actually reduce in size after a certain point, this keeps up the static pressure for rooms that are farther away. Think of it like this, if you blew air through a 3 inch pipe, and then blew an equal amount through a 1 inch pipe, the pressure would feel stronger in the 1 inch pipe. The duct system does this the same way, by going through the larger duct first and then farther away it gets smaller to keep static pressure consistent.
Pl advise best software or manuals Round / circular process duct calculation including, Expansion joint, Stiffner, development, Load calculation on each support
Michael, 16" won't be adequate for 3 tons or even 2.5 tons IF you are using flex duct. One way to see this is to use 550 FPM as the upper limit for the velocity in flex. Any faster and you will rapidly increase the pressure drop and noise. A 16" duct has a 1.4 sq. ft. cross-section. At 550 FPM you can deliver 770 CFM of air. That's really not enough for even 2 tons of cooling if you figure at 400 CFM/ton. Air flow could be 350-450 CFM/ton depending on local humidity conditions.
Yeah ok for 25 years I've been using 16 inch return flex for 3 ton and no problems and the longer the better for less noise. You can read all the books you want go and install and you'll find out what your doing really fast or you'll have customers chasing you with pitch forks
Why not go with a 3 ton? Just curious. You’ll have 68 extra cfm. Instead of 268 extra cfm. Ik you can’t install a over size unit of your evap coil will freeze up do to air flow restriction. Wouldn’t a 3 ton be more effective cooling the rooms and more efficient?
I'm no expert, but 3 tons for a 1200 sq ft house w/ average ceilings seems like it's way too big unless you have a lot of windows or very little insulation. If you oversize the system, it will cycle often and be less efficient. Variable speed units will help this, but still seems silly to oversize so much.
That's based off of doing a Manual J. Wall thickness, number of windows, direction of walls, exterior wall exposure, type of insulation under slab or crawlspace and in attic, etc. all determine tonnage of unit.
Why not get the cubic footage for each room multiplied by the needed air changes per room divided by 60. Do that to each room and add it all up to get your total CFM. By getting your total CFM needed, wouldn't that give you the tonnage you need for the unit?
Been doing this for years...we both could take a year long. Class on air flow and we would probably still disagree and go round and round as to how size ducts...
Hey man nice job, but we need to stop telling people to use .1 static. Every equipment has different friction loss, it's up to the HVAC company designing the system to know what that is. With variable speed motors, electronic air cleaners, and other add-ons you could be either under sizing or over sizing the duct work causing premature break downs of new equipment, higher power bills, and poor humidity levels in the home. I hate to be the party pooper, but too many times do I run into poor duct work and it's from this old school logic that we always use .1 when designing duct work. Times have changed, units are more efficient and homes are tighter which offset a lot of these old school practices. Please, I just want homeowners to stop yelling at me when I tell them why their 3 year old system broke down. Thanks man.
I need 162 CFM in one room which is 25Ft away from unit. Ruler showing me 14" round flex!!! Is that ok or I ma reading something wrong ? I have this slide rule tool.
NO! WRONG! CFM is sized by heat loss/ heat gain not by square footage. Dont do this, corner rooms, 2 exterior walls and 2 partitions walls will not have enought air while rooms with 3 partitions walls and one exterior wall will have to much air.
@@psmopar existing home. I have a 3 ton unit and I have the sq footage of all the bedrooms and the distance to all the rooms and it's pretty much a straight shot to all the rooms. But I dont know the duct size. And I thought I knew the cfms according to this video but everyone in the comments says its incorrect. But with the way he found it my different duct sizes look like the appropriate size but I'm not sure And also my living room has one duct coming from the handler and then it split into two ducts that both go into the living room. That's the lne I'm having most problems sizing
@@bruced9668 I'm confused, how are you sizing the duct? by the 3 ton system and assuming you have 1200 cfm from the air handler? You do or don't know the size of the exiting duct? what is your goal to patch up the living room as that is not cooling correctly?? What type of air handler gas or electric?
@@psmopar The air handler is electric. All the existing flex air ducts arent the correct, one of my cousins installed them in this house 15 years ago.. I have a 3 ton and yes I believe that's 1,200 available cfms. I'm not sure how to calculate the cfms needed for each room. I thought this video showed how to find each rooms cfm in the beginning. I know the sqft of each room and I know the distance from the air handler to each vent. I have 10 air vents, 2 of them are in the living room. One air duct feeds the 2 vents in the living room.
Heat load wrong. 10*12 = 120 sq ft by thumb rule 1 TR = 120 sq ft so 1 TR = 400 Cfm Total sq ft = 1268 So 10.50 TR required 10.50*400 = 4200 CFM required for whole rooms.
Хобби
Thank you so much for this. Love my Super Cool Slide Rool. I never leave home without it.
Great tutorial. Thank you for taking the time to make this video.
For those wondering about the ceiling affecting the CFM to each room:
I think the ceilings where accounted for during the initial load calculation to size the equipment using Manual J.
Since you have the proper number of tons from your system, then what he did was divide the total CFM output of the unit by the total square footage of the home so you end up with .788 Feet per minute. When you multiply that by the square footage of each room you get cubic feet per minute again.
Clean tutorial is very cool & has inspired me to buy your tool.
Super Cool is on it's way!!
love this tool!!! I have one question, can I use this for ventilation applications too?
s
Great video, it'll be a big help in my house design. I hate to be a stickler for details, but @1:17 your cfm calc is off on your 22x20 room. Should have been 352 and you have it at 76.8 (such as for your 8x12 room)
Yes, probably a copy and paste issue!! nw
Super cool for sure.great vid.
Great computations!
Good tutorial.God bless you
Fyi to Supercool, bottom right calculated number needs to be 352 (not 76.8)
Yep
This is a brief tutorial and is not intended to be a solution for all duct sizing applications. If you are an architect or an engineer might I suggest that you properly perform load calculations and use the latest duct sizing software, but for everyone else in the world this duct sizing method will work in 95% of the applications. If you lack the common sense to know that a room with 12 foot ceilings will require more air than a room with 8 foot ceilings, I would suggest you find a different line of work.
Can u please give me ur WhatsApp no,
I want to talk u about ducting size please.
My WhatsApp no is
00923129797912
I farted and it stunk. How much ventilation air do I need to not stink up the rest of the house?
That's a neat tool. 👌
I am adding vaulted ceilings but will have closed cell spray foam on roof/walls and rim joists. Should I then still calculate for higher ceilings?
Basic ok tool for the typical ranch or row house, but how about a more complex duct system? One should really use manual J to figure the load per room, and then manual D to size ducting. To use only .1 for supply friction is a bit misleading, I find quite a few of my installations have friction rates for supply ducting at more like .05. I am laying out a duct system tonight which as 460 equivalent feet of duct from the farthest return to the farthest supply. .1 is for 100 equivalent feet of duct not 460?
You guys need to add this to the app store!
Thanks alot!!!!!!!! it is useful!!
Hani A. /
If celing heights vary wouldn't it be more accurate to calculate the cubic feet of each room and divide the cfm up proportional to the cubic feet rather than the square feet?
I think the ceilings were accounted for during the initial load calculation to size the equipment using Manual J.
Since you have the proper number of tons from your system, then what he did was divide the total CFM output of the unit by the total square footage of the home so you end up with .788 Feet per minute. When you multiply that by the square footage of each room you get cubic feet per minute again.
First I’m just a home owner interested in learning ,I always thought there was a crazy math to figuring out the dimension of the and then the duct size ,with your book it’s not as hard as I once thought ,so thank for making that easier to understand for me ,
My question is just figure the area of the room doesn’t factor in how far away the room is from the unit , Now if the unit is (this my home)basementand the biggest room in the house are right above the unit on the 1st floor and by rule those rooms would have larger ducts then the smaller room above them , would most of the air pressure die off by the time it reached the 2nd and even more by the 3rd floor ,dose the length of the duct work not get factored in at , again I don’t install and I am only concluding on my experience, can any explain how I can check calculate my ducts to make sure the sizes are correct, thanks again I will continue learning more to be an educated consumer
Hi, I am in trade school now. For rooms that are farther away, the trunk line (the main line spanning the house) will actually reduce in size after a certain point, this keeps up the static pressure for rooms that are farther away. Think of it like this, if you blew air through a 3 inch pipe, and then blew an equal amount through a 1 inch pipe, the pressure would feel stronger in the 1 inch pipe. The duct system does this the same way, by going through the larger duct first and then farther away it gets smaller to keep static pressure consistent.
How do you figure out your main trunk size
Why .1 for supply and .05 for return?
Is it because you’re going by the available static Pressure left for the return and supply
Why not install adjustable air diffusers and then just adjust air flow for comfort?
Pl advise best software or manuals
Round / circular process duct calculation including, Expansion joint, Stiffner, development, Load calculation on each support
Michael, 16" won't be adequate for 3 tons or even 2.5 tons IF you are using flex duct. One way to see this is to use 550 FPM as the upper limit for the velocity in flex. Any faster and you will rapidly increase the pressure drop and noise. A 16" duct has a 1.4 sq. ft. cross-section. At 550 FPM you can deliver 770 CFM of air. That's really not enough for even 2 tons of cooling if you figure at 400 CFM/ton. Air flow could be 350-450 CFM/ton depending on local humidity conditions.
Yeah ok for 25 years I've been using 16 inch return flex for 3 ton and no problems and the longer the better for less noise. You can read all the books you want go and install and you'll find out what your doing really fast or you'll have customers chasing you with pitch forks
Where can I get this chart
Great video can u send me the text data for cfm calculate as u shown in video .
How do you get 400 per ton and why are multiplying it by 2.5??
This is precisely this and the most interesting - they, as always, do not finish speaking - in order to seem smarter than everyone.
Why not go with a 3 ton? Just curious. You’ll have 68 extra cfm. Instead of 268 extra cfm. Ik you can’t install a over size unit of your evap coil will freeze up do to air flow restriction. Wouldn’t a 3 ton be more effective cooling the rooms and more efficient?
i was kind of leaning towards this line of thinking.. i need to learn more.
I'm no expert, but 3 tons for a 1200 sq ft house w/ average ceilings seems like it's way too big unless you have a lot of windows or very little insulation. If you oversize the system, it will cycle often and be less efficient. Variable speed units will help this, but still seems silly to oversize so much.
can any one plzz explain hvac formulas .....................
thank you
MD Chowdhury supecoo
Supercool siliderule.com
How can I order it ?
Everyone says to use .1 friction loss but I can’t find any answers as to why it’s .1 what makes this the nominal number to use?
How did you assume 2.5 tons for given sq footage? How do we calculate that please help
That's based off of doing a Manual J. Wall thickness, number of windows, direction of walls, exterior wall exposure, type of insulation under slab or crawlspace and in attic, etc. all determine tonnage of unit.
Why not get the cubic footage for each room multiplied by the needed air changes per room divided by 60. Do that to each room and add it all up to get your total CFM. By getting your total CFM needed, wouldn't that give you the tonnage you need for the unit?
how do you know air changes needed ? Tonnage required is also dependent on heat load. How well is room insulated ? how many windows ?
Been doing this for years...we both could take a year long. Class on air flow and
we would probably still disagree and go round and round as to how size ducts...
Anyone can tell me what cfm is for 7in x 14in return joist ?
14 x 6 is 400cfm and 14 x 8 is 600 cfm so 500 cfm.
Hey man nice job, but we need to stop telling people to use .1 static. Every equipment has different friction loss, it's up to the HVAC company designing the system to know what that is. With variable speed motors, electronic air cleaners, and other add-ons you could be either under sizing or over sizing the duct work causing premature break downs of new equipment, higher power bills, and poor humidity levels in the home. I hate to be the party pooper, but too many times do I run into poor duct work and it's from this old school logic that we always use .1 when designing duct work. Times have changed, units are more efficient and homes are tighter which offset a lot of these old school practices. Please, I just want homeowners to stop yelling at me when I tell them why their 3 year old system broke down. Thanks man.
That's why there's extra equations for static loss recovery and for friction loss etx
HEY BOSS IF YOU ACTUALLY HAVE ONE OF THESE CALCS IT HAS THE CORRECTED PRESSURE DROP TABLE ON IT. HIS SYSTEM MIGHT HAVE BEEN .1 AFTER CORRECTION
Make into an app and yea 16 was ok when u said 20
The math is off on your chart. 440sq *.8 is 352 not 76.8
I thought return was .8
I need 162 CFM in one room which is 25Ft away from unit. Ruler showing me 14" round flex!!! Is that ok or I ma reading something wrong ? I have this slide rule tool.
+srokalapy No way is that correct
Ruler is showing me 10"
srokalapy b
NO! WRONG! CFM is sized by heat loss/ heat gain not by square footage. Dont do this, corner rooms, 2 exterior walls and 2 partitions walls will not have enought air while rooms with 3 partitions walls and one exterior wall will have to much air.
Can you help me find my cfms
@@bruced9668 What is it that you are looking for, existing home, new home?
@@psmopar existing home. I have a 3 ton unit and I have the sq footage of all the bedrooms and the distance to all the rooms and it's pretty much a straight shot to all the rooms. But I dont know the duct size. And I thought I knew the cfms according to this video but everyone in the comments says its incorrect.
But with the way he found it my different duct sizes look like the appropriate size but I'm not sure
And also my living room has one duct coming from the handler and then it split into two ducts that both go into the living room. That's the lne I'm having most problems sizing
@@bruced9668 I'm confused, how are you sizing the duct? by the 3 ton system and assuming you have 1200 cfm from the air handler? You do or don't know the size of the exiting duct? what is your goal to patch up the living room as that is not cooling correctly?? What type of air handler gas or electric?
@@psmopar The air handler is electric. All the existing flex air ducts arent the correct, one of my cousins installed them in this house 15 years ago..
I have a 3 ton and yes I believe that's 1,200 available cfms. I'm not sure how to calculate the cfms needed for each room. I thought this video showed how to find each rooms cfm in the beginning.
I know the sqft of each room and I know the distance from the air handler to each vent.
I have 10 air vents, 2 of them are in the living room. One air duct feeds the 2 vents in the living room.
440 X .8 is 352 not 76.8
Doing videos like this we Don't assume. And is not a 1.5 ton unit.
Lol
Heat load wrong. 10*12 = 120 sq ft by thumb rule 1 TR = 120 sq ft so
1 TR = 400 Cfm
Total sq ft = 1268
So 10.50 TR required
10.50*400 = 4200 CFM required for whole rooms.
Two 16in flex ducts for a 2.5 ton system!? What blasphemy is this.
OMG