Air Conditioning Condensate Calculator

This Condensate Calculator, adapted for the Web from a spreadsheet created by Eddie Wilcut and Elliott Fry at the San Antonio Water System, can be used to estimate the production of air-conditioning condensate—which can be used as an alternative water source—in a commercial building. Condensate production is a function of the temperature and relative humidity of the outdoor air, the target conditions in the building (temperature and relative humidity), and the amount of cooling that is provided in the building.


To use this condensate calculator, enter the appropriate outdoor and indoor conditions: temperature (in degrees-Fahrenheit) and percent relative humidity. Then set the cooling system output in tons of cooling (one ton of cooling is equal to 12,000 Btus per hour). Lastly, enter Percentage of Outside air, which is the portion of the total enclosed volume of the building that is replaced by introduced outside air via mechanical ventilation, based on a daily average.

The grains of moisture per cubic foot of air (gr/ft3) are listed for both the outdoor and indoor conditions, but this information (and the difference) is usually of less interest than the gallons of water produced for a given time period—provided at the bottom of the calculator.


There are many factors that go into calculating an accurate view of condensate production in a building. This online calculator uses a simplified equation and should be applied accordingly. For a more detailed view, consider using modeling software, and/or the services of a qualified engineer.