Which data are required to evaluate heat flow through a building envelope using the conductive heat loss formula?

• A. Wind speed, humidity, thickness.
• B. Area, temperature difference, RSI.
• C. Color, surface texture, emissivity.
• D. Roof slope, solar gain, HVAC efficiency.

Answer: (D)

The key idea is that conductive heat loss through a building envelope depends on how much area is exchanging heat, how big the temperature difference is across that boundary, and how well the boundary conducts heat (its thermal transmittance).

To evaluate this with the conductive heat loss formula, you need:

• the area of the envelope portion in contact with the other environment (A),

• the temperature difference between inside and outside (ΔT),

• and the material’s ability to conduct heat, expressed as RSI (or the derived U-value, where U = 1/RSI).

If RSI is given, you can compute the heat flow using Q = U × A × ΔT, with U = 1/RSI. For example, with RSI = 3.5 m^2K/W, A = 20 m^2, and ΔT = 15 K, Q ≈ (20/3.5) × 15 ≈ 86 W.

Other factors listed, like wind speed, humidity, color, emissivity, roof slope, solar gain, or HVAC efficiency, influence heat transfer in ways other than straightforward conduction (they affect convection, radiation, or overall energy balance) and are not the data you use in the pure conductive heat loss calculation.