The short answer
Treat the label watts as an upper bound per hour of running, then measure real use over several days with a plug-in meter. A basement unit in a damp week can be one of the largest plug-in loads in the house; the same unit in a dry week can cost almost nothing.
Rated watts versus how it actually cycles
A dehumidifier runs its compressor until the room reaches the humidity you set, then idles with only the fan or nothing at all. Ambient temperature matters too: below about 65°F many compressor units cycle to defrost their coils and remove far less water per kWh. So the arithmetic in the calculator needs the hours the compressor actually ran, which you do not know until you measure.
Worked examples
| Scenario | kWh / day | kWh / period | Cost / period |
|---|---|---|---|
| 500 W × 4 h/day (dry-ish room) | 2 | 60 | $12.00 |
| 500 W × 12 h/day (damp basement) | 6 | 180 | $36.00 |
| Meter read 38 kWh after 7 days | 5.429 | 162.857 | $32.57 |
Basis: Round-number illustrations using a 500 W nameplate and assumed run hours. The run hours are the unknown; they are shown as a range to make the point, not as a measurement.
Measuring yours
Plug the meter in for a full week if you can: humidity swings with weather, laundry and showers. Check the dehumidifier's label against the meter's rating (the P4460 manual states 15 A and 1,875 W). Put the kWh and days into the calculator's meter mode and compare the monthly figure with the change on your bill from the diagnostic.
Do not stop needed moisture control to save electricity
If the unit is keeping a basement below the humidity where mould grows, switching it off costs more than it saves. EPA guidance is to control moisture at its source; a cheaper way to run the dehumidifier is a better humidity setpoint, a drain hose instead of a bucket, and fixing the leak or grading problem feeding the damp.
P3 International Kill A Watt P4400
Single meterA week-long measurement on one outlet is exactly what this meter is for. Choose an outlet nobody will disturb, since it resets if unplugged.
You want to measure one plug-in appliance at a time, read the number off the meter and do the cost arithmetic yourself.
Hardwired appliances, 240 V dryers or ranges, anything above the meter's rated load, wet locations, or a measurement you cannot afford to lose if the meter is unplugged.
- Confirm the maximum ratings printed on the unit label of the exact item you buy.
Sources and evidence
What we are relying on
- Energy cost for a steady load = watts ÷ 1,000 × hours per day × days × your rate in dollars per kWh.
- Arithmetic method, not a measurement. Appliances that cycle on and off need measured kWh or actual runtime, not nameplate watts × 24 hours.
- The P4460 manual specifies measurement ranges up to 125 V rms, 15 A rms and 1,875 W and restricts use in wet locations. The unit label states the maximum ratings.
- Verified from the manufacturer or official document. A rating limit does not make every appliance suitable; follow both the meter and appliance instructions.
- EPA guidance is to fix the source of a moisture problem. Sealing a window does not resolve an existing moisture issue.
- Verified from the manufacturer or official document.
What this page does not establish
- No dehumidifier was measured for this page; run hours in the examples are assumptions, not observations.
- Water removed per kWh depends on temperature and humidity and is not addressed here.
Sources
- Estimating appliance and home electronic energy use, Virginia Cooperative Extension. Calculation method; read 2026-09-07.
- Kill A Watt EZ P4460 operation manual, P3 International. Manufacturer document; read 2026-09-07.
- A brief guide to mold, moisture and your home, U.S. Environmental Protection Agency. Official guidance; read 2026-09-07.
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