Duct sizing for furnace

Started by cedarglen, October 19, 2009, 11:11:42 PM

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cedarglen

We're building the Universal 2 story as a 20x32'. I'm ready to rough in my ducts and need some help on sizing. I will have the furnace on the 1st (lower) floor. I'm thinking that I'll have two ducts comming off the top of the furnace. One will shoot up through the second story to the attic where I will branch it off to each of the different rooms and the vents will be in the cieling. The other will go down through the 1st story floor to the buildup  below the house where it will branch off to each room and the vents will be in the floor. What size should these two main ducts be? Or does anybody have a better way of doing it? All input welcome.

thank you,
Chuck

n74tg

Have you done a google search on duct sizing?  I know there is a internet based rental program out of Canada named HVAC-Calc that will tell you what size unit you need as well as duct sizes, but it isn't free.  I think for about $25 you get a 30 day use of the program, or at least that's about what I paid to use it a year or two ago.  It's a good program and based on ACCA Manual J calculation method, which I think is pretty much state of the art.

Good luck; let us know whatever you figure out. 
My house building blog:

http://n74tg.blogspot.com/


ScottA

Proper duct and furnace sizing requires taking alot of things into consideration such as location, facings, glass area, insulation, heat load from appliances computers etc. but if you want the quick and dirty method.
These are boot sizes-
Bath 4"
small bedroom 6"
kitchen 6"
laundry 4"
living room 2x 6"
walk in closet 4"
Dining 6"
Try to place the vents infront of windows and near doors. You want to bath the outside walls in air. For duct sizes break it down into wyes such as 6x4x4 8x6x6 etc. You may want to put a 6" over the stairs as well.

ScottA

I read that you want to go up and down? Bad idea. I'd suggest using 2 units. 1 in the attic and one on the ground floor. You'll have a hard time getting one unit to blow both ways. The other option would be to put it under the house and blow only up.  Also you'll need return air on both floors even if only using 1 unit.