Heat loss calculation

I just consider the house as an aggregate envelope - the room-by-room allocation of baseboard capacity has already been done by MSI heating engineers. There are five sources of heat loss: walls, windows, basement, attic, and infiltration. I presume 0 deg outside temp and 65 deg inside temp. Considered in turn:

• Exterior walls comprise 2851 sq.ft., at R20 lose 9266 btu/hour.


• Exterior windows comprise 573 sq.ft., at U=0.34 lose 12663 btu/hour.


• Basement ceiling is 1142 sq.ft., at R20 lose 1428 btu/hour (assumes basement at 40 deg soil temperature).


• Attic roof is 1600 sq.ft, at R20 lose 5196 btu/hour.


• Attic gable walls are 250 sq.ft., at R20 lose 813 per hour.


• Infiltration assuming 0.4 ACH (9000 cu.ft.) lose 10689 btu/hour.

Total is 40,000 btu/hour. I think the 0.4 infiltration is conservative, and the house should actually be in the 0.2-0.3 range according to its construction practices.