Grow Room Exhaust Fan Calculator
Extraction for a sealed or vented grow room.
Enter your values
ⓘ Live results
Results
- 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)
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.
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.
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.