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View Full Version : I NEED HELP!!!!!!!!!!!!

kipfisher
09-21-2005, 06:51 PM
i've been doing commercial duct work for a while. i always do well on the work i am assigned, but i always have the prints to show me what to do. i just told a friend i would run the duct work in the house he is building and was shocked to see his prints had no duct work on them. now i have no idea how to figure out materials. how many CFMs does each size round duct carry? i have a 3 1/2 ton unit with both plenum sizes 14 1/2 x 14 1/2, unit specs is 1150CFMs and the house is 1512sqft. how do i figure out my materials given this information.

BaldLoonie
09-21-2005, 06:57 PM
Some flaws here.

He must be building it pretty poorly to need 3.5 tons in a 1500 sq ft home :(

Also, you say unit spec is 1150 CFM but for 3.5 tons ought to have more capacity than that.

First, someone needs to do an accurate heat gain/loss calc. If it really needs that much cooling, he should build the place right to reduce the gain & loss. That's sorry for new construction.

Then get a hold of ACCA's Manual D and study it. Butcher his duct system and he'll remember you for life - or at least as long as he is in his uncomfortable house.

2hot2coolme
09-21-2005, 07:00 PM
You never have any HVAC drawings on blueprints for residential, well I can't say never, once in a while the architect will draw all his/her oversized crap, your kinda screwed, time to go back to school and learn calculation & design classes or pay someone to come out and design it for you while you do the labor.

happycamper
09-21-2005, 07:03 PM
cuz it sounds like your in over your head and if it goes wrong you just lost a friend..

Irascible
09-21-2005, 07:33 PM
Originally posted by BaldLoonie
He must be building it pretty poorly to need 3.5 tons in a 1500 sq ft homeEither that or he likes it 68 degrees in the house on a 105 degree day. We fat people sweat a lot. ;^)

kipfisher
09-21-2005, 07:38 PM
ok well thanks everybody

dan sw fl
09-21-2005, 08:32 PM
Originally posted by kipfisher
How many CFMs does each size round duct carry?

i have a 3 1/2 ton unit with both plenum sizes 14 1/2 x 14 1/2, unit specs is 1150 CFM and the house is 1512 sq ft. how do i figure out my materials given this information.

CFM per duct size = ~ 600 FPM * Duct Area ( Sq.Ft.)

Send me drawing + Window Schedule and SHGC
and I'll tell you CFM per room.
Location : ____ ?

I'll re-check capacity ( 26,000 BTU h Sensible ? ) required.

[Edited by dan sw fl on 09-21-2005 at 08:37 PM]