Sorry......flex duct doesn't readily come to (my) mind because we use so little of it here.
Originally Posted by duckman06
Dampers are a must in every situation IMHO.
Originally Posted by arc8
I thought you were referring to a minimum velocity needed to help "push" the air or some other notion.
70k input @ 95% eff, divided by 1.08, then by 60F = 1026CFM.
Of course you could also use a smaller furnace and AC. AC in northern climates frequently get oversized because too high of a design temperature is used. Most of Vermont is between a 81-84F design temperature with 69F wet bulb. 1.5 tons should be plenty. 2 tons at most if there were a lot of windows and minimal shade.
A 120 sq ft room may only need 60 CFM. The sq ft of a room doesn't determine how much air that room needs for heating or cooling.
Originally Posted by M.Dubbs
Your 28X8 supply duct is ok for 1200 CFM.
There are many 2800 sq ft homes that don't have anywhere near 2800 CFM of air flow.