This is a great place to learn, thank you all that have answered my questions. Here is the next one. I just completed an audit and they only have a heater that is ducted because they are in a beach community. It was very leaky, but leaky compared to what??? I have read through my BPI and can't find some kind of multiplier for heater duct leakage
21.7 times the OUTPUT btu= cfm for heat Example: 100,000 btu furnace input 80,000 btu furnace output. 80% efficient.
21.7 X 80=1736 cfm supply for heat. You have to go outside BPI for these formula's. Try national comfort institute. The 80 comes from dropping the zero's from 80,000 btu
thank you both, ahhh I forgot my HERS stuff. Yes, when I saw 21.7 I remembered HERS. See somtimes a little nudge is all we need. I guess I couldn't think of putting HERS and BPI together. Thanks much appreciated.