Supply Air Temperature Rise Calculator
Furnace temperature rise from CFM and BTU.
Enter your values
Enter the furnace output in BTU/hr.
Enter the system 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.
- Temperature rise
- 52.9 °F
- Assessment
- Within typical rated range
Quick answer
Temperature rise across a furnace equals its heat output divided by 1.08 times the system airflow in CFM.
ΔT = BTU/hr output / (1.08 x CFM)
At a glance
| What it does | Furnace temperature rise from CFM and BTU. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Furnace output, System airflow |
| Main output | Temperature rise |
| Formula | ΔT = BTU/hr output / (1.08 x CFM) |
| Cost | Free — no sign-up, no download |
How to use the Supply Air Temperature Rise Calculator
- 1Enter the furnace's rated heating output in BTU per hour.
- 2Enter the system's actual airflow in CFM at the current blower speed.
- 3Compare the resulting temperature rise to the furnace nameplate's rated rise range.
Inputs explained
- Furnace output(BTU/hr)
- Enter the furnace output in BTU/hr.
- System airflow(CFM)
- Enter the system airflow in CFM.
Worked example
Using the values the calculator loads with:
Inputs
- Furnace output80000 BTU/hr
- System airflow1400 CFM
Results
- Temperature rise52.9 °F
- AssessmentWithin typical rated range
Frequently asked questions
Why does temperature rise matter?
Running outside the furnace's rated rise range risks overheating the heat exchanger or delivering lukewarm air.
How do I fix a high rise?
Check for a dirty filter, closed dampers or undersized ducts restricting airflow, or increase blower speed.
What do I need to enter into the Supply Air Temperature Rise Calculator?
Just 2 values: furnace output, system 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 Supply Air Temperature Rise Calculator work out the answer?
Temperature rise across a furnace equals its heat output divided by 1.08 times the system airflow in CFM. It applies the formula ΔT = BTU/hr output / (1.08 x CFM) and shows the working so you can check each step by hand.
Is the Supply Air Temperature Rise 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.