Humidifier CFM Calculator
Duct humidifier capacity from airflow and target RH gain.
Enter your values
ⓘ Live results
Results
- Estimated output needed
- 370.3 gallons/day
- Grains added per minute
- 1800
- Suggested unit class
- Steam humidifier
Quick answer
Duct humidifiers are sized in gallons per day based on system CFM, outdoor design temperature and the target indoor relative humidity.
GPD approx = CFM x grains removed x 60 / 7000 / 24
How to use the Humidifier CFM Calculator
- 1Confirm the furnace or air handler's rated CFM.
- 2Estimate the grains of moisture per pound of air you need to add for your climate.
- 3Match the gallons-per-day figure to a humidifier's rated output.
Worked example
Using the values the calculator loads with:
Inputs
- System airflow1200 CFM
- Grains of moisture to add per lb air20 grains/lb
Results
- Estimated output needed370.3 gallons/day
- Grains added per minute1800
- Suggested unit classSteam humidifier
Frequently asked questions
What grains figure should I use?
Colder climates with dry winter air often need 15-25 grains/lb added; mild climates need less.
Steam vs bypass humidifiers?
Steam units add moisture independent of airflow and suit tighter, well-insulated homes.
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.