Ventilation & Carbon Filter Sizing Calculator
Size your inline fan and carbon filter from room volume, air exchange target, and duct losses.
Covers filter aging, heat spikes, and running the fan below full speed.
Loss factors. Each one reduces effective airflow.
About 5% loss each.
Required fan rating
0
CFM
- Room volume
- 0 ft³
- Base CFM
- 0 CFM
- After climate factor
- 0 CFM
- Total loss
- 0%
- CFM needed to overcome losses
- 0 CFM
- With headroom
- 0 CFM
| Loss factor | Loss |
|---|
Match your carbon filter to the fan's rated CFM, not the base requirement. Mount the filter on the exhaust side.
How this is calculated
Base CFM = room volume ÷ exchange time in minutes. Required CFM = base × climate factor ÷ (1 − total loss fraction) × (1 + headroom). Simple mode assumes a standard carbon filter (20%), 10 ft of flexible duct, and one 90° bend. Fan size suggestions use common inline fan ratings: 4 inch up to about 190 CFM, 6 inch up to about 440 CFM, 8 inch up to about 750 CFM, 10 inch up to about 1,000 CFM.