Whole-Building Heat-Loss Coefficient UA
The whole envelope rolled into one number a degree-day estimate and a balance-point calc both start from: UA = sum(A_i/R_i) + 1.08 x CFM (Btu/h-F). A small house of R-17 walls, R-38 ceiling, R-3 windows, and R-19 floor with 50 cfm infiltration sums to 309.7 Btu/h-F - times a 70 F design difference, a 21,700 Btu/h load. Air-seal to 25 cfm and upgrade the glass to R-5 and the load drops 17%, the two biggest levers a roll-up exposes. Sensible only; enter the natural infiltration cfm. An energy-audit aid, not a stamped Manual J.
Formula and source
cond = sum(A_i / R_i); UA_inf = 1.08 x CFM; UA = cond + UA_inf; design_load = UA x dT.
The whole-building heat-loss-coefficient roll-up UA = sum(A/R) + 1.08 x CFM with the design load Q = UA x dT, as compiled in the ASHRAE Fundamentals and RESNET energy-audit references, by name.
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