Hong Life CalculatorsUnderstanding the dehumidifier running cost calculator — concept and principle
A dehumidifier pulls moisture out of indoor air to prevent condensation, mould and musty smells, and it often runs for many hours a day during wet seasons. This calculator turns the unit's power rating and your daily running time into monthly energy use and monthly and yearly cost, so you can budget for it or compare models.
How it is calculated
- kWh per month = W ÷ 1000 × hours per day × days per month
- Monthly cost = kWh per month × price per kWh
- Yearly cost = monthly cost × 12
Power (W) is the rated input power on the label. Hours per day is how long the unit actually runs, not how long it is switched on. Days per month lets you model seasonal use, for example 30 days in the rainy season and fewer in dry months.
The principle
Energy equals power × time, and 1 kWh is 1,000 W sustained for one hour. Most home units are compressor (refrigerant) types: a cold coil cools the air below its dew point so water condenses and drips into the tank, then a warm coil reheats the air. Desiccant types absorb moisture with a material that is dried by a heater; they usually draw more power but keep working in cold rooms where a compressor coil can ice up. With a built-in humidistat, the compressor stops once the target humidity is reached, so real running hours are often fewer than the hours the unit is on.
Worked example
- Inputs: 300 W, 10 hours per day, 30 days, $0.25 per kWh.
- Power in kW: 300 ÷ 1,000 = 0.3 kW.
- Monthly energy: 0.3 × 10 × 30 = 90 kWh.
- Monthly cost: 90 × $0.25 = $22.50.
- Yearly cost: $22.50 × 12 = $270.00.
| Power (W) | Monthly cost |
|---|---|
| 75 | $5.63 |
| 150 | $11.25 |
| 225 | $16.88 |
| 300 | $22.50 |
| 375 | $28.13 |
| 450 | $33.75 |
| 600 | $45.00 |
How to read the result
The yearly figure assumes the same use all year; most homes need a dehumidifier only part of the year, so scale the days accordingly. To compare units, look at the water removed per kWh rather than wattage alone: a model that removes more litres per kWh reaches the target sooner and runs fewer hours. Setting the humidistat sensibly matters too. The US EPA advises keeping indoor humidity below 60%, ideally between 30% and 50%; drying the air further costs energy without much extra benefit.
Common mistakes
- Counting all the hours the unit is switched on instead of compressor running hours.
- Running it with windows open, which brings in fresh humid air.
- Ignoring the room temperature: compressor units remove much less water in cold rooms.
Frequently asked questions
Is it cheaper to run a dehumidifier or the air conditioner's dry mode?
It depends on the two machines' efficiency and the room. Enter each one's measured power and hours here and compare the results.
How many hours a day should a dehumidifier run?
As long as needed to hold your target humidity. A hygrometer tells you when that is reached.
Does a dehumidifier help with heating costs?
A compressor unit releases its input energy plus the latent heat of the condensed water into the room, so it slightly warms the space.
Sources: U.S. Environmental Protection Agency — A Brief Guide to Mold, Moisture, and Your Home · International System of Units (SI), BIPM