Furnace Temperature Rise Calculator

Temperature rise must fall within the range on the furnace rating plate.

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Formula

Rise = supply − return
CFM ≈ output ÷ (1.08 × rise)

Example calculation

Supply 125 °F, return 68 °F → 57 °F rise; 76,800 BTU/h output → ≈1,248 CFM.

Practical HVAC use

Verify airflow during furnace start-up.

Common mistakes

Measuring supply in line-of-sight of the heat exchanger.

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Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators