Grow Room Exhaust Fan Calculator
Extraction for a sealed or vented grow room.
Enter your values
Enter the total heat load in W.
Enter the allowed temperature rise in °F.
Enter the room volume in cu ft.
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.
- Fan size
- 790 CFM
- Heat removal requirement
- 632 CFM
- Air exchange requirement
- 320 CFM
- Heat load
- 4,094 BTU/h
- Air changes achieved
- 148 ACH
Quick answer
Extraction must remove both stale air and light heat; the heat load usually sets the fan size in a sealed room.
CFM = watts x 3.412 / (1.08 x allowed °F rise)
At a glance
| What it does | Extraction for a sealed or vented grow room. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Total heat load, Allowed temperature rise, Room volume |
| Main output | Fan size |
| Formula | CFM = watts x 3.412 / (1.08 x allowed °F rise) |
| Cost | Free — no sign-up, no download |
How to use the Grow Room Exhaust Fan Calculator
- 1Add up the wattage of lights, pumps and ballasts in the room.
- 2Set the temperature rise you can live with over intake air — 5–8 °F is realistic.
- 3Size the fan on whichever requirement is larger, then add 25% for filters.
Inputs explained
- Total heat load(W)
- Enter the total heat load in W.
- Allowed temperature rise(°F)
- Enter the allowed temperature rise in °F.
- Room volume(cu ft)
- Enter the room volume in cu ft.
Worked example
Using the values the calculator loads with:
Inputs
- Total heat load1200 W
- Allowed temperature rise6 °F
- Room volume320 cu ft
Results
- Fan size790 CFM
- Heat removal requirement632 CFM
- Air exchange requirement320 CFM
- Heat load4,094 BTU/h
- Air changes achieved148 ACH
Frequently asked questions
Why is my room still hot?
Either the fan is undersized for the heat load or intake air is already warm — you cannot exhaust below ambient.
Do LEDs change this?
LEDs make less heat per usable photon, but every watt drawn still becomes heat in the room.
What do I need to enter into the Grow Room Exhaust Fan Calculator?
Just 3 values: total heat load, allowed temperature rise, room volume. 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 Grow Room Exhaust Fan Calculator work out the answer?
Extraction must remove both stale air and light heat; the heat load usually sets the fan size in a sealed room. It applies the formula CFM = watts x 3.412 / (1.08 x allowed °F rise) and shows the working so you can check each step by hand.
Is the Grow Room Exhaust Fan 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.