GeneralAire home comfort tools

Whole House Humidifier Sizing Calculator

Use this humidifier capacity calculator to estimate the moisture output your home may need, in gallons per day. Start with your home’s size and the indoor conditions you want to evaluate.

This estimate uses General Filters’ published sizing table at 0.5 air changes per hour. A licensed HVAC contractor should confirm equipment size for your climate, construction, ventilation and installation.

Include the basement in the area to be humidified.

These humidity choices are sizing scenarios, not recommended thermostat settings. Colder outdoor conditions can require lower indoor humidity to prevent condensation.

Estimated moisture output

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gallons per day (GPD)

Enter your home details, then select Calculate moisture needs.

The estimate assumes 0.5 air changes per hour.

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How to choose the right size humidifier

Use the estimated gallons per day as a starting point, then ask your HVAC contractor to compare it with each model’s rated output and installation requirements. A larger home or higher air leakage can change the capacity you need.

How this estimate is calculated

Home area × average ceiling height gives the volume in cubic feet. We multiply that volume by the published factor for your selected temperature and relative humidity, then by 1.05 for each fireplace. Multiplying the resulting pounds of moisture per hour by 2.88 gives gallons per day.

The available temperature and humidity choices match the manufacturer table. This tool does not model local weather or adjust the table for other air change rates. Final capacity also depends on the home’s air leakage, ventilation and system operating conditions.

Source: GeneralAire DS15P / DS25 / DS25LC specification sheet, page 2 (June 2018 PDF), and General Filters FAQs.