Evaporator Coil Temperature Difference

Coil TD shows how hard the evaporator is working relative to the air across it.

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Formula

TD = entering air temperature − saturated suction temperature

Example calculation

75 °F return air, 40 °F saturation → 35 °F TD.

Practical HVAC use

Low TD can suggest low airflow-independent issues; high TD can suggest low airflow or a dirty coil. Compare with design data.

Common mistakes

Confusing coil TD with supply–return ΔT.

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Calculate sensible heat in BTU/h and kW from airflow and temperature difference using Q = 1.08 × CFM × ΔT, with metric inputs.

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