Delta T Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026How to measure temperature split
- Let the system run for at least 15 minutes to stabilize.
- Measure the return air temperature near the air handler intake.
- Measure the supply air temperature at a nearby register or the supply plenum.
- Select cooling or heating mode and enter both readings below.
Worked example
For a cooling-mode system with a 75 F return and 55 F supply:
deltaT = 75 - 55 = 20 F (within the normal range)
A properly functioning cooling system typically produces a 16-22 F split; readings well outside that range are one of the fastest field diagnostics for airflow problems (dirty filter, undersized ductwork, weak blower) or refrigerant charge issues, without needing to attach refrigerant gauges first.