Modifying existing duct work
Without seeing the actual system and knowing what kinds of ducts you have (hard metal or flexible, etc.), it is hard to say exactly what you should do. Static pressure drop and airflow (in cubic feet per minute, or CFM) is all related to this. You would need to do a heat loss calculation on your home as well (including wall insulation info, windows, doors, direction the rooms face, where you live, etc., etc.) to determine how much air you need in a room.... or, you could "dumb it down" and just approximate how many CFM per square foot you need in certain rooms (depending on room usage and wall direction, whether you had big windows, etc.). Residential usage is typically anywhere from 0.4 to 1.0 CFM/sqft.
All that being said, from your sketch (well done, BTW), some basic ideas:
-Make sure that if you change around your ducting, you keep about the same cross-sectional area within the ducts... i.e., if you want to combine two 7" round ducts to be one main duct, those are each about 38.5 sq. in. of area, so two would be about that would come out to be about 77 sq. in., which is approx. a 10" round, or, say, a 10x8 rectangular).
-Make sure, if you have flexible duct, to straighten out any kinks and make any turns as long and smooth as possible.
-Obviously, if you can seal any leaks, that is good too.
Last edited by pjpjpjpj; 04-05-2007 at 10:38 AM.