Dehumidifier running cost calculator

Understanding Dehumidifier Running Costs

A dehumidifier costs less to run than many people expect, but the actual figure depends on the machine's wattage, how often you run it, and your electricity tariff. This calculator helps you estimate the daily, weekly and monthly cost so you can budget properly before buying.

What affects running cost?

• Wattage most home dehumidifiers range from 200W (compact models) to 700W (large capacity or commercial units).
• Hours per day running continuously costs more but is only needed for severe damp problems. Most homes need 4-8 hours a day in winter.
• Electricity tariff the biggest variable, and the one people most often get wrong. UK domestic rates have moved a lot in recent years, so use the pence-per-kWh figure printed on your own bill rather than an average. The calculator defaults to 28p.
• Room temperature compressor units are less effective below 15C and may run longer to extract the same amount of moisture.
• Humidity target aiming for 40% RH versus 60% RH means the machine works harder and runs longer.

Quick cost reference (at 28p per kWh)

These are estimates. The calculator below gives you a personalised figure based on your machine's wattage and your tariff.

Why your real cost differs from the estimate

The calculator multiplies rated wattage by hours, which gives a deliberately cautious answer. In practice a dehumidifier with a humidity setpoint cycles on and off once it reaches the target, so it rarely draws its rated power for the whole run. Real consumption is commonly 40-70% of the rated figure in a room that reaches its setpoint, and close to 100% in a cold garage or a room with a continuous moisture source.

Three things push the cost past the headline figure:

• A cold room. Compressor units lose efficiency below roughly 15C and run longer to extract the same water. A 200 W compact unit in a cold bedroom can draw more over a night than a 400 W unit in a warm living room.
• Drying laundry. A wet wash load is a large, sustained moisture source, so the unit runs at full output for the whole session instead of cycling.
• A low humidity target. Aiming at 40% RH rather than 55-60% means the unit runs longer for little practical benefit in most homes.

Worked examples

Three realistic households, using an assumed 25p per kWh. Check your own tariff - the figure on your bill is the one that applies to you.

The pattern is consistent: a correctly sized compressor unit in a warm room is cheap to run, and a desiccant unit in a cold space is not. That is not an argument against desiccant units - they are the sensible choice in an unheated garage - but it is a reason to draught-proof before buying one.

How to cut the cost

• Set a humidity target rather than running on a timer. Around 50-55% RH is comfortable and stops the unit once the room is dry.
• Fix draughts and close the door. Drying air you are not trying to dry is the biggest single waste.
• Size it correctly. An undersized unit runs all day and still fails to dry the room; a correctly sized one finishes and switches off.
• Drain continuously if you run it for hours. A unit that has tripped out on a full tank is costing money and doing nothing.
• Take the chill off a very cold room. Raising a cold room towards 18C makes a compressor unit markedly more efficient.
• Deal with the cause. A leak, a failed seal or bridging damp will keep the unit running indefinitely - start with the damp and condensation checklist.

Related guides and tools

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