Which three factors are used to calculate heat loss?

• A. Design temp x U value x area
• B. Design temp x area x humidity
• C. U value x area x insulation thickness
• D. Design temp x U value x distance

Answer: (A)

Heat loss through a surface is driven by three things: the temperature difference between inside and outside, how easily heat can pass through the surface (the U-value), and the area of the surface through which the heat flows. In steady-state conduction, the rate of heat loss is calculated as Q = U × A × ΔT, where ΔT is the indoor temperature minus the outdoor design temperature, U is the overall heat transfer coefficient, and A is the surface area. This is why the correct factors are design temperature, U-value, and area.

Humidity and distance aren’t part of this basic conduction formula. Insulation thickness does affect the U-value (thicker or better-insulated layers typically reduce U), but you use the U-value in the calculation, not thickness directly.