STEP 7: Calculate the heat loss through infiltration by crack method q (Btu/h) = 1.1 * V (cfm) * DT (°F) V (cfm) = S(P*leakage rate) each window V (cfm) = 18*(3’ + 3’ + 4’ + 4’)*(0.10 cfm/ft) = 25.2 cfm q (Btu/h) = 1.1 * (25.2 cfm) * 80.1 °F = 2,220 Btu/h
