Delta T HVAC Calculator
Supply and return split with a health verdict.
Enter your values
ⓘ Live results
Results
- Delta T
- 19 °F
- Verdict
- Healthy split
- Sensible capacity
- 24,624 BTU/h
- In tons
- 2.05
Quick answer
A healthy air conditioner shows a 16–22 °F drop between return and supply air; a furnace shows the rise printed on its data plate.
ΔT = return temp − supply temp
How to use the Delta T HVAC Calculator
- 1Measure return air at the filter grille and supply air a few feet into the duct.
- 2Enter both temperatures and the system airflow.
- 3Compare the split with the healthy range for that mode.
Worked example
Using the values the calculator loads with:
Inputs
- ModeCooling
- Return air temperature75 °F
- Supply air temperature56 °F
- Airflow1200 CFM
Results
- Delta T19 °F
- VerdictHealthy split
- Sensible capacity24,624 BTU/h
- In tons2.05
Frequently asked questions
My split is only 10 °F — what now?
Check for a dirty filter, a blocked coil, low charge or a blower running too fast.
Should I measure at the register?
Measure in the plenum or near the coil; register temperature is warmed by duct gains.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.