How to use the calculator
- Use typical conditions, not the best day. Take the average afternoon temperature and humidity for the season you care about. Your weather app or the National Weather Service lists both.
- Enter the machine’s real power draw. A 50-pint home dehumidifier, the usual donor for a DIY build, draws about 500 watts. A plug-in watt meter gives the exact figure.
- Pick the machine type. Leave it on “typical” unless you know better. Choose “old or leaky DIY” for salvaged parts in a home-made cabinet.
- Set your electricity price. It is on your utility bill. The U.S. residential average is roughly 17 to 18 cents per kWh, and state averages range from about 11 cents to over 40.
Reading the result
| Result | What it means | Our advice |
|---|---|---|
| Under 2 gallons a day | Air too dry or too cold for a cooling coil | Skip the build. Store water instead. |
| 2 to 5 gallons a day | Drinking and cooking water for one or two people, at a high cost per gallon | Worth it only as a backup with power available. |
| 5 to 9 gallons a day | Drinking and cooking water for a family | A sensible project in your climate. |
| Over 9 gallons a day | You entered a large machine or very humid air | Check the electricity line: the cost scales with it. |
Try three runs: your best month, your typical month and your driest month. A machine that makes seven gallons in August and one in January is a seasonal tool, and you should plan storage around that.
Reference results
The same model, run for seven kinds of weather with a 500-watt typical compressor unit:
| Climate | Air temp / humidity | Dew point | Gallons per day | Power cost per gallon | Power needed for 60 gal/day |
|---|---|---|---|---|---|
| Hot and humid Gulf Coast summer | 88 °F / 75% | 79 °F | 8.5 | $0.24 | 3.5 kW |
| Warm and humid Southeast, late spring | 80 °F / 70% | 69 °F | 7.1 | $0.29 | 4.2 kW |
| Rated test point classic dehumidifier test condition | 80 °F / 60% | 65 °F | 6.0 | $0.34 | 5.0 kW |
| Mild air-conditioned room | 70 °F / 50% | 50 °F | 3.6 | $0.56 | 8.3 kW |
| Cool and damp coastal Northwest, basement | 55 °F / 80% | 49 °F | 4.3 | $0.47 | 7.0 kW |
| Warm and dry Mountain West afternoon | 85 °F / 30% | 50 °F | 0.5 | $4.06 | 59.7 kW |
| Hot desert Southwest summer | 100 °F / 15% | 44 °F | ≈ 0 | — | not achievable |
How the model works
The calculator starts from how dehumidifiers are rated. A typical compressor unit removes about 1.9 liters of water per kWh at 80 °F and 60% relative humidity. It then asks how conditions at your location differ.
- Dew point. Computed from temperature and humidity with the Magnus formula.
- Coil temperature. Assumed to run 7 °C below the dew point, no more than 20 °C below the air temperature, and never below freezing.
- Latent share. The fraction of cooling that condenses vapor, as opposed to merely chilling air. At the rated point this is about 43%; in dry air it drops toward zero.
- Efficiency. Rated liters per kWh, multiplied by the latent share relative to the rated point, with a penalty when the coil is near freezing and loses time to defrosting.
- Output. Efficiency × power × hours.
What the model leaves out
- Air leaks and poor airflow in a home-built cabinet, which reduce output.
- Day and night swings. Humidity is usually higher at night, so real daily totals can beat an afternoon-based estimate.
- Altitude. Thinner air carries slightly less water at the same humidity.
- Desiccant machines, which follow different rules and work at lower humidity.
The model reproduces published dehumidifier behaviour reasonably well: about 75% of rated capacity at 65 °F and 60% humidity, and about 135% at 80 °F and 80%. Treat any single result as accurate to within roughly 30%.
Why the answer is never 60 gallons
The Water Freedom System sales page advertises “up to 60 gallons a day”. Set the calculator to its best case, hot and very humid, and a 500-watt machine returns 8 to 9 gallons. To reach 60 you must raise the power to about 3,500 watts, which is no longer a $200 project or something a wall outlet can run. More on that claim →
Common questions
How much water does a dehumidifier make per day?
A unit sold as “50-pint” removes up to 50 pints, or 6.25 gallons, in 24 hours under test conditions of 65 °F and 60% humidity. In warmer, wetter air it makes more; in drier air, less.
What humidity do I need to make water from air?
For a cooling-coil machine, a dew point above about 55 °F: for example 75 °F at 50% humidity, or 90 °F at 32%. Below that, output and efficiency fall quickly.
Is the calculator accurate for commercial AWG machines?
Reasonably, if you pick “high efficiency” and enter the unit’s rated wattage. Manufacturers publish output at a stated temperature and humidity; compare like with like.
Can I embed or cite this calculator?
You are welcome to link to it and to quote results with attribution to Water Freedom System Plans.
Sources
- ENERGY STAR, Dehumidifiers (capacity ratings and test conditions).
- National Weather Service, dew point calculator (to cross-check dew points).
- U.S. Energy Information Administration, average retail price of electricity by state.