Hvac duct design

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  #1  
Old 04-08-19, 03:49 PM
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Hvac duct design

Doing my third personal home hvac install....but first requiring ductwork installation as well.
Anyone here familiar enough with sizing requirements?
I have 5 ton 2 stage unit going in attic. All drops from ceiling. want to run 2 trunks...1 down both sides of house,,,with one trunk slightly longer than the other. I understand the room sizing calculator to a degree for each vent....but what diameter should the main trunks be?
I can draw a diagram if anyone willing to give me a hand.
Thanks.
 
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Old 04-08-19, 05:48 PM
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The main trunk needs to be designed to handle the maximum CFM from the air handler. And it needs to then be reduced to handle the reduced CFM with each takeoff.
Manual D is used for duct design. Along with a room by room manual J.
Your looking at 2,000 CFM.
 
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Old 04-09-19, 03:15 PM
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Will upload pics of floor plan later but plan on attic install running 2 trunks down each side of house. Charts say 19 or so inches at 2000cfm but am figuring 16 because length of runs around 40 to 50 foot each and also flow loss with gas burner and splitting in half at blower. Question is if I split output at blower do I drop to 8 inch runs each side since wont be a closed loop at end of the run.
Forgot to mention would like to run round duct...but may have to run rectangular duct.
 

Last edited by isosphere; 04-09-19 at 03:18 PM. Reason: duct
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Old 04-09-19, 03:44 PM
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Attached are the pics of design. Bottom side is roughly 40 foot run....top side is roughly 50 to 55 foot run with a couple 90 degree turns up and over through a room to get to eaves to hit bedroom and bathroom on left side upper corner of first floor diagram Also just notice 2nd floor diagram rotate 180 degrees.....ac system is over dining room....lol
 
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Old 04-09-19, 04:12 PM
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Just wanted to add if not for anything else to make me feel better getting off my chest....my !*%%$! neighbor supposedly owned a HVAC company. Met him before I bought house 5 months ago. He said 10 to 12 k to do whole job. I budgeted 15k just in case. Took months to get him out...finally brings his partner out and quotes me 20 to 22k...lol Tells me he is a small partner....but messed up either way. Doing myself then gonna invite him over for a beer with house cranked to 60 degrees and offer him a sweater.,,,,lol.
I dont expect anyone to do anything for free but he was not even close in his estimate.
 
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Old 06-14-19, 05:42 AM
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How was 5 ton's found to be the correct size without a heat load being done? If a heat load was done then just convert that to room by room and you will know how many CFM will be needed for each room. FYI 20 inch spiral will be good for 2000cfm and 14-16 will be good for 1000
 
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