Moisture Removal Calculator
Work out how much water an air conditioner coil or dehumidifier is taking out of the air — in pints per day, pounds per hour and gallons of condensate.
Method reviewed October 26, 2026. Version 1.0.0. How it works
Result
- Water removed per day
- 176.1pints
- Water removed per hour
- 7.647lb/h
About 176.1 pints a day (7.65 lb/h) of water removed.
- Dehumidifier ratings are measured at the test conditions named in the rating; output falls in cooler, drier air.
- Condensate per hour
- 0.917gal/h
- Latent heat removed (approx.)
- 8,114BTU/h
- Entering humidity ratio
- 92.1gr/lb
- Leaving humidity ratio
- 61.1gr/lb
Show the working
- Humidity ratios (ASHRAE equations)92.09 → 61.1 gr/lb
- Dry-air flow = CFM × 60 ÷ specific volume400 × 60 ÷ 13.893 ft³/lb = 1,727 lb/h
- Water removed = dry-air flow × ΔW1,727 × 0.004427 = 7.647 lb/h
- Pints per day = lb/h × 24 ÷ 1.042 lb per pint176.1 pints/day
How it is calculated
The calculator finds the humidity ratio — pounds of water per pound of dry air — of the entering and leaving air with the ASHRAE psychrometric equations. The airflow is converted to pounds of dry air per hour using the entering air’s specific volume, and the water removed is that flow times the drop in humidity ratio.
A US pint of water weighs about 1.042 lb, so pints per day = pounds per hour × 24 ÷ 1.042. Each pound condensed releases about 1,061 BTU of latent heat, which is the moisture part of the cooling load.
Readings matter
Humidity is the hard part to measure: a few percent of relative humidity changes the answer noticeably. Measure entering and leaving air close to the coil, after the system has run steadily, with a calibrated instrument.
Worked example
These are the example values the calculator opens with, and the result the engine calculates for them.
Inputs
- Airflow through the coil
- 400 CFM
- Entering air temperature
- 80 °F
- Entering relative humidity
- 60 %
- Leaving air temperature
- 55 °F
- Leaving relative humidity
- 95 %
- Site elevation
- 0 ft
Result
- Water removed per day
- 176.1 pints
- Water removed per hour
- 7.647 lb/h
- Condensate per hour
- 0.917 gal/h
- Latent heat removed (approx.)
- 8,114 BTU/h
- Entering humidity ratio
- 92.1 gr/lb
- Leaving humidity ratio
- 61.1 gr/lb
About 176.1 pints a day (7.65 lb/h) of water removed.
Assumptions
- Dry-air mass flow is based on the entering air’s specific volume. 1 US pint of water ≈ 1.042 lb; latent heat ≈ 1,061 BTU/lb (the constant in the ASHRAE enthalpy equation).
Limitations
- Needs accurate humidity readings; a few percent RH error changes the result noticeably.
Frequently asked questions
How much water should my AC remove?
It depends on airflow, humidity and how long it runs. A typical home system in humid weather can remove many gallons a day; short cycles remove much less.
Why does my dehumidifier remove less than its rating?
Ratings are measured at specific test conditions. In cooler or drier air, dehumidifiers remove less water.
How big a condensate pump do I need?
The gallons-per-hour figure shows the water to be moved; choose a pump with comfortable margin and follow its manufacturer’s instructions.
Sources
- PsychroLib — psychrometric functions after ASHRAE Handbook—Fundamentals (2017) ch. 1 — PsychroLib (open source, MIT licence). Humidity ratio W = 0.621945·pw/(p − pw), wet-bulb, enthalpy and standard-atmosphere equations as published by ASHRAE.
- NIST Guide to the SI (SP 811), Appendix B.9 — conversion factors — National Institute of Standards and Technology. 1 ton of refrigeration = 12,000 BTU/h; 1 BTU/h = 0.2930711 W; 1 atm = 101.325 kPa.
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