Which formula correctly estimates BTU/h from airflow and temperature rise?

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Multiple Choice

Which formula correctly estimates BTU/h from airflow and temperature rise?

The main idea is converting the heat carried by moving air into a BTU per hour value using how much air flows and how much its temperature rises. The correct formula is BTU per hour equals CFM times ΔT times 1.08, where CFM is cubic feet per minute and ΔT is the temperature rise in °F. The 1.08 factor comes from combining air density, the air’s specific heat, and converting minutes to hours: ρ × cp × 60 ≈ 0.075 lb/ft^3 × 0.24 BTU/(lb·°F) × 60 ≈ 1.08. So the heat transfer rate is determined by how much air passes (CFM), how hot it gets or cools by (ΔT), and this conversion constant. If you omit the 1.08, you’d understate the heat moved because you’re missing the time and air-heat properties in the conversion. If you drop CFM or rely only on ΔT, you ignore either the amount of air or the actual temperature change, which makes the estimate meaningless for a flow system. A factor of 10 would overestimate by tenfold. This formula is commonly used for quick estimates of cooling or heating load across a coil or in an air handler when you know the airflow and the resulting temperature rise.

The main idea is converting the heat carried by moving air into a BTU per hour value using how much air flows and how much its temperature rises. The correct formula is BTU per hour equals CFM times ΔT times 1.08, where CFM is cubic feet per minute and ΔT is the temperature rise in °F. The 1.08 factor comes from combining air density, the air’s specific heat, and converting minutes to hours: ρ × cp × 60 ≈ 0.075 lb/ft^3 × 0.24 BTU/(lb·°F) × 60 ≈ 1.08. So the heat transfer rate is determined by how much air passes (CFM), how hot it gets or cools by (ΔT), and this conversion constant.

If you omit the 1.08, you’d understate the heat moved because you’re missing the time and air-heat properties in the conversion. If you drop CFM or rely only on ΔT, you ignore either the amount of air or the actual temperature change, which makes the estimate meaningless for a flow system. A factor of 10 would overestimate by tenfold. This formula is commonly used for quick estimates of cooling or heating load across a coil or in an air handler when you know the airflow and the resulting temperature rise.

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