Which HVAC calculation would require knowledge of BTUs?

When sizing a furnace, knowledge of BTUs (British Thermal Units) is essential because BTUs are the measurement of thermal energy. This unit indicates the amount of heat necessary to raise the temperature of one pound of water by one degree Fahrenheit.

In the context of heating systems, a furnace's output is rated in BTUs per hour, which helps determine the capacity needed to efficiently heat a given space based on its square footage, insulation quality, and the local climate. Properly sizing a furnace means matching its BTU output to the heating requirements of the home; this ensures the furnace operates effectively, maintains comfort levels, and maximizes energy efficiency.

The other choices, while related to building performance, do not directly involve BTU measurements. Assessing insulation quality relates more to R-values and thermal resistance, measuring duct airflow speed focuses on air velocity rather than thermal energy, and calculating structural integrity pertains to load-bearing and material strength, which are not associated with thermal calculations. Thus, the knowledge of BTUs is specifically applicable and critical in the context of furnace sizing.