Electricity basics
Appliance Duty Cycle: Why 24 Hours Is Not Full Power
Understand duty cycle and cycling appliances. Estimate active time carefully, include other modes, and use measured kWh when average power is unknown.
Duty cycle is the share of time a component operates. A cycling appliance may be plugged in all day without drawing full power all day. Other modes can still use energy.
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A fridge can stay plugged in for 24 hours while its compressor switches on and off. A dehumidifier can stop removing moisture after reaching its humidity target. These changes affect electricity use.
Duty cycle describes the share of time a component runs. It is useful for a simple estimate, but it does not describe every operating mode inside an appliance.
Define the period and the component
If a compressor runs for six hours during a 24-hour record, its duty cycle for that record is 6 ÷ 24 = 25%.
That does not mean the complete appliance consumes no power during the other 18 hours. Controls, a fan, or a separate heater may draw energy. Identify which component your active-time percentage describes.
The ENERGY STAR dehumidifier guide explains humidistat control. A humidity target can cause operation to change with the moisture load rather than follow a fixed daily schedule.
Calculate a simple active-load scenario
Suppose a hypothetical component draws 400 W while active. If it operates for 25% of a 24-hour day, active-load energy is 400 ÷ 1,000 × 24 × 0.25 = 2.4 kWh.
If another mode draws 10 W for the remaining 18 hours, add 10 ÷ 1,000 × 18 = 0.18 kWh. Total example energy becomes 2.58 kWh, not 2.4.
At an example $0.20/kWh, that total costs $0.516, or about $0.52. These are illustrative powers and timings. They are not a typical specification for any appliance.
Do not guess a universal percentage
Room temperature, heat gain, door openings, humidity, and the chosen target can change operation. A percentage observed during a mild day may fail during a heatwave.
Variable-speed devices create another complication. The ENERGY STAR room-AC page explains that some compressors change their output rather than simply alternate between full power and off.
For those devices, a binary “active percentage” can hide changes in power while running. Time alone is not enough unless the active wattage is also representative.
Prefer cumulative kWh for changing loads
A suitable electricity monitor can integrate these stages into one cumulative energy reading. The P3 manual describes energy and elapsed-time readings for its compatible loads.
The DOE standby test guidance also discusses averaging fluctuating power from energy measured over time. Your household check should not be described as a formal lab test.
- Select a normal observation period.
- Record cumulative kWh and elapsed time.
- Note the appliance's settings and room conditions.
- Divide energy by time to obtain an average.
- Repeat under materially different conditions.
Use a duty-cycle estimate honestly
The electricity calculator has an active-share field for a stated-power estimate. It scales only the entered watts. It does not automatically add standby, fan-only operation, or defrost energy.
Use 100% for a genuinely steady draw. If you do not know the active share, compare explicit scenarios rather than assigning a precise-looking guess. Better still, use measured daily kWh.
Keep the period with the result. “25% on this day” is a clear observation. “This appliance always runs at 25%” needs much stronger evidence.
Sources
Source pages checked during research on 7 October 2026. Examples are Handy Daily calculations unless stated otherwise.