Duct Sizing

sdbrown1

Hello all and thanks in advance to you

I have a house 1st, 2nd,3rd floor. My question is, what size duct should i use for each floor?

does the 6 inch duct give more of an illusion of force on the room end as apposed to the 8 inch duct

Diesel65

Nowhere near enough info, how many units, what size, appx square foot of each floor, hard duct mains or all-flex system, would be a start.

A 6" flex carrying the same cfm's of air as an 8" will have a higher velocity but will also need an increase in static pressure to accomplish, there-by creating a problem with the design of the rest of the system.
A 6" flex will carry appx 225 cfm's at the Trane recommended max (for residential) of 1200 feet per minute.

An 8" will carry appx 420 cfm's to carry 420 cfm's in a 6" flex you would need appx 2400 feet per minute FPM which is twice as much as the average residential design will allow (getting on for nearly 2.0 static) which a standard a/c system cannot produce.

sdbrown1

the house is 2200 sq feet. I intend to use sheet metal type ducting.

able14

recomended cfm for 6 inch is 100 cfm and around 220 for 8 inch you need to do a heat loss heat gain by room to see what size duct you need to run

national

what does everyone usually use as a standard for a 12x13 room..id use 1 7 or 2 6's normally

thom

12X13 is borderline 1 @ 6". any larger would be 2@7'. Two windows in the room would bump it up to two as would a skylite. This is with refrigerated air. Evaporative cooling would require boosting duct size to 7".

I am in a moderate climate (Albuquerque). A harsh climate could change things as could a more moderate climate.