Delta T HVAC Calculator
Supply and return split with a health verdict.
Enter your values
Choose one of: Cooling, Heating.
Enter the return air temperature in °F.
Enter the supply air temperature in °F.
Enter the airflow in CFM.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Supply and return split with a health verdict. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Mode, Return air temperature, Supply air temperature, Airflow |
| Main output | Delta T |
| Formula | ΔT = return temp − supply temp |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Mode
- Choose one of: Cooling, Heating.
- Return air temperature(°F)
- Enter the return air temperature in °F.
- Supply air temperature(°F)
- Enter the supply air temperature in °F.
- Airflow(CFM)
- Enter the airflow in CFM.
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.
What do I need to enter into the Delta T HVAC Calculator?
Just 4 values: mode, return air temperature, supply air temperature, airflow. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Delta T HVAC Calculator work out the 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. It applies the formula ΔT = return temp − supply temp and shows the working so you can check each step by hand.
Is the Delta T HVAC Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.