How Much Does a Dehumidifier Cost to Run?

To estimate a dehumidifier's running cost, divide its input watts by 1,000, multiply by the hours it actively draws that power, then multiply by your electricity unit rate. A 200W machine drawing full power for six hours uses 1.2kWh.

At an example rate of £0.25 per kWh, that costs £0.30. Use the unit rate on your own bill because tariffs change.

Calculate my dehumidifier running cost

The basic calculation

Electricity is billed in kilowatt-hours, written kWh. One kilowatt-hour is the energy used by a 1,000W appliance drawing that power for one hour.

Ofgem's bill guidance explains that the unit rate is charged per kWh.

Use these steps:

• Convert watts to kilowatts: watts ÷ 1,000.
• Calculate energy: kilowatts × hours used.
• Calculate cost: kWh × electricity price per kWh.

The daily standing charge is not caused by the dehumidifier, because you pay it whether the appliance runs or not. Leave it out when comparing the extra cost of using the machine.

Find the correct wattage

Use electrical input power from the rating label, manual or manufacturer specification. Do not use litres per day: that measures nominal water extraction, not electricity. Do not use tank capacity or confuse power with annual energy.

Some manufacturers publish power at a stated temperature and relative humidity. Different fan speeds, laundry programmes or desiccant heater settings may have different inputs.

If the documentation gives a range, calculate more than one scenario or measure the actual machine.

Worked example: small compressor model

Suppose a compressor dehumidifier is rated at 160W and is used for eight hours:

• 160W ÷ 1,000 = 0.16kW.
• 0.16kW × 8 hours = 1.28kWh.
• 1.28kWh × £0.25 = £0.32.

That is an upper-style session estimate if 160W is drawn for every entered hour. If the compressor switches off for part of the session, actual energy can be lower.

Worked example: larger compressor model

For a 250W unit running at full input for six hours:

• 250W ÷ 1,000 = 0.25kW.
• 0.25kW × 6 hours = 1.5kWh.
• 1.5kWh × £0.25 = £0.375, which rounds to about £0.38.

If used on seven days under the same full-input assumption, the weekly estimate is £2.63. It should not be presented as a guaranteed bill because room conditions and cycling change.

Worked example: desiccant model

For a 650W desiccant machine running for four hours:

• 650W ÷ 1,000 = 0.65kW.
• 0.65kW × 4 hours = 2.6kWh.
• 2.6kWh × £0.25 = £0.65.

The per-hour cost is higher than in the compressor examples. That alone does not prove the complete job costs more: a desiccant machine may remove water more effectively in a cold space or complete a laundry session sooner.

Compare energy over the same outcome and conditions.

Why watts multiplied by 24 hours can exaggerate use

Many compressor dehumidifiers use a humidistat. While humidity is above the target, the compressor and fan work. Once the target is reached, the compressor may stop and restart later.

Some models keep the fan running continuously; others sample the air periodically. The manual is the only reliable description of the exact control behaviour.

Multiplying rated input by 24 therefore answers a narrow question: what would it cost if the unit drew that input for all 24 hours? It can be useful as a conservative comparison, but it may overstate normal steady-state consumption after the room has dried.

During the first days in a damp space or while drying laundry, the compressor may run for a larger share of the time.

Humidity target, temperature and airflow

A very low humidity target makes the appliance work harder and may be unnecessary. Cold conditions reduce compressor extraction, while an open door or window can continuously add untreated air. A blocked filter also reduces airflow.

These factors affect runtime without changing the wattage printed on the label.

Capacity can affect session length. A larger model may draw more power while active but reach the target sooner; a smaller one may use less per hour but run longer. There is no honest universal claim that either always costs less.

Compare published inputs and, where possible, measure real energy.

Use your current unit rate

Energy prices vary by tariff, region, payment method and date.

Ofgem updates its price-cap unit rates, but your bill remains the right source for your calculation.

If you have peak and off-peak rates, use the rate that applies when the machine runs or calculate each period separately.

Measure for a better answer

A plug-in energy monitor can record kWh over several typical days. Start with a known humidity target, record room temperature and note laundry sessions. Divide total measured cost by days or loads for a useful personal estimate.

Use only a monitor with an appropriate electrical rating and follow its instructions.

Do not compare machines only on advertised pence per hour. Check the electricity rate and wattage behind the claim, the date it was calculated, the test conditions and whether the machine is appropriate for the space.

Choose the machine before estimating the bill

The cheapest unsuitable dehumidifier is poor value.

Use the SetupSelect dehumidifier finder to identify a suitable technology and capacity, then enter the shortlisted model's watts in the running-cost calculator.

For capacity trade-offs, read 12L vs 20L dehumidifiers; for cold-room energy decisions, read compressor vs desiccant.