Cooling Tower Airflow Calculator
Airflow and evaporation for a cooling tower.
Enter your values
Enter the water flow in gpm.
Enter the range (in - out) in °F.
Enter the air enthalpy rise in Btu/lb.
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.
- Heat rejected
- 3,000,000 BTU/h
- In tons
- 250
- Airflow
- 55,556 CFM
- Evaporation
- 6 gpm
- Makeup with 3 cycles
- 9 gpm
Quick answer
Cooling tower airflow is set by the heat rejected and the enthalpy rise of the air passing through the fill.
CFM ≈ heat rejected / (4.5 x enthalpy rise)
At a glance
| What it does | Airflow and evaporation for a cooling tower. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Water flow, Range (in - out), Air enthalpy rise |
| Main output | Heat rejected |
| Formula | CFM ≈ heat rejected / (4.5 x enthalpy rise) |
| Cost | Free — no sign-up, no download |
How to use the Cooling Tower Airflow Calculator
- 1Enter the condenser water flow and the range you need across the tower.
- 2Use 10-14 Btu/lb enthalpy rise for a typical induced draft tower.
- 3Add blowdown to evaporation to size makeup water.
Inputs explained
- Water flow(gpm)
- Enter the water flow in gpm.
- Range (in - out)(°F)
- Enter the range (in - out) in °F.
- Air enthalpy rise(Btu/lb)
- Enter the air enthalpy rise in Btu/lb.
Worked example
Using the values the calculator loads with:
Inputs
- Water flow600 gpm
- Range (in - out)10 °F
- Air enthalpy rise12 Btu/lb
Results
- Heat rejected3,000,000 BTU/h
- In tons250
- Airflow55,556 CFM
- Evaporation6 gpm
- Makeup with 3 cycles9 gpm
Frequently asked questions
What is approach?
The gap between leaving water temperature and ambient wet bulb — a 5°F approach tower is much larger than a 10°F one.
Cycles of concentration?
Higher cycles save water but need better chemical treatment to avoid scale.
What do I need to enter into the Cooling Tower Airflow Calculator?
Just 3 values: water flow, range (in - out), air enthalpy rise. 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 Cooling Tower Airflow Calculator work out the answer?
Cooling tower airflow is set by the heat rejected and the enthalpy rise of the air passing through the fill. It applies the formula CFM ≈ heat rejected / (4.5 x enthalpy rise) and shows the working so you can check each step by hand.
Is the Cooling Tower Airflow 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.