Formula for sizing feeder ducts?

[Onewolf]

I'm curious if there's a formula or utility to determine the number/size of feeder ducts required based upon square footage of a room?

I have a 916 sq ft room (28'4x32'4") with 10ft ceilings and I was wondering if there's a formula for calculating the theoretical number/size of feeder ducts? For instance would five 8" ducts be sufficient? too much?

 

[zmaxmotorsports]

How many windows and doors in the room,what is it being supplied by?

 

[Onewolf]

Zero windows (there are two windows but they will be blocked out and insulated) and one door. It's a Trane TAM4A0A30 2.5 ton heat pump supplying three rooms (40 sq ft, 140 sq ft, 916 sq ft).

 

[volleyball]

Heat calc will give you a needed sq in. size. total. Figure your duct size and how many to fulfill that requirement

 

[bazar01]

Get hold of a Manual D book on sizing and designing residential duct system.
There is also a Manual J for calculating heat gain/loss of the rooms that accounts for insulation value of walls, floors and ceilings, windows R-value, orientation (E,W,N or S), etc.