A dehumidifier pulls moisture out of the air, which helps with condensation, musty smells and drying washing indoors. By the standards of a kettle or an oven it is not a heavy electricity user, but because people tend to leave one running for hours at a stretch, the cost of that habit is worth understanding before you buy or before you let it hum away all winter. The good news is that the numbers are usually smaller than people fear, and in one common use it can actually save you money.
What a dehumidifier actually draws
Most domestic dehumidifiers pull somewhere between 150 and 700 watts while the compressor is working, a long way below a tumble dryer or an electric heater. The exact figure depends on the type, the capacity and how hard the unit is having to work. The important point is that a dehumidifier with a humidistat does not run flat out the whole time it is switched on: once the air reaches the target humidity the compressor cycles off, and the unit then draws only the small power its fan and electronics need until the air gets damp enough to trigger it again. So the plate rating is the most it will ever use, not the average across a day. A plug-in energy monitor is the quickest way to see what yours really pulls over a typical run, and the reading is often lower than the label suggests.
Compressor versus desiccant
There are two common types and they behave quite differently on the meter. A compressor, or refrigerant, dehumidifier chills a cold surface so moisture condenses out of the air, working on much the same principle as the back of a fridge. These are the more efficient choice in a normal heated home and are what most people should buy. A desiccant dehumidifier instead uses a moisture-absorbing wheel and a built-in heater to drive the water back off, which means it draws more power for the same amount of water removed, often half as much again or more. In return it keeps working well in a cold space where a compressor model struggles, so an unheated garage, a chilly utility room or a caravan over winter is where the desiccant type earns its higher draw. In a warm living room the compressor type wins comfortably on cost.
What a session costs
Because the compressor cycles on and off, working out a day's cost means estimating how long it actually runs, not how long it sits switched on. Suppose a 300 watt compressor unit runs for, on average, half of an eight-hour stint, so four hours of real compressor time, or about 1.2 kWh. At an example 28p per unit that is roughly 34p for the day. Keep that up across a damp autumn and winter, say a hundred such days, and you are looking at somewhere around 34, plus a little for the fan time in between. A larger or harder-working unit in a very damp house could be two or three times that. Drop your own model's wattage and a realistic run time into the running cost calculator for a figure that matches your home rather than a guess.
Drying laundry with one
This is where a dehumidifier often pays for itself outright. Drying clothes on an airer in a closed room with a dehumidifier running typically uses far less electricity than a tumble dryer, which is one of the hungriest appliances in the house, as the tumble dryer guide sets out. The dehumidifier lifts the evaporated moisture straight out of the air so the washing dries in hours rather than days, without the windows streaming and without feeding mould on the walls. For anyone with no tumble dryer, or trying to wean themselves off one, it sits neatly between a cold flat draped in slowly drying laundry and an expensive dryer. The drying without a tumble dryer guide covers the wider set of options it fits into.
The damp and condensation angle
The reason most people buy a dehumidifier in the first place is not really to save energy but to deal with condensation, musty smells and black mould on cold walls and around window reveals. Damp air also feels colder than dry air at the same temperature, so it takes a little more heating to feel comfortable, which means drier air can sometimes let you nudge the thermostat down a touch for a small indirect saving. But running a dehumidifier is treating the symptom rather than the cause. If the moisture is coming from poor ventilation, from drying washing on radiators, or from cold bridging where a wall meets a window, the machine hides the problem rather than curing it. It earns its place as part of the answer, not as the whole of it.
Sizing and running it well
A unit is rated by how many litres it can pull from the air in a day, and a bigger capacity is not automatically better to live with. A right-sized unit reaches the target humidity and then idles quietly; an oversized one mostly just costs more to buy and runs hard when it does not need to. Set the humidistat to a sensible target, somewhere around 50 to 60 per cent relative humidity, rather than the lowest setting, which only makes it run far longer for steadily diminishing comfort. Close the door of the room you are treating or drying in so the machine is not fighting the moisture of the whole house at once. Empty the tank promptly, or fit a continuous drain hose, so it does not switch off and let the air re-dampen overnight. And keep the air filter clean, because a clogged filter makes the fan labour for less effect.
When a dehumidifier is the wrong tool
If your damp is rising damp, a plumbing leak or penetrating damp soaking through a wall, a dehumidifier does nothing about the cause and you end up paying to run it indefinitely. The same is true when condensation is really a ventilation problem in disguise: a kitchen or bathroom with no working extractor, trickle vents painted shut years ago, or a home sealed so tightly after enthusiastic draught-proofing that moist air simply has nowhere to escape. In those cases better ventilation, a proper repair, or warming up the cold surface is the real fix, and sometimes a cheaper one than running a machine forever. The dehumidifier is brilliant at managing moisture; it is no substitute for stopping it at the source.
The bottom line
A dehumidifier is a modest electricity user that can genuinely save money when it stands in for a tumble dryer, and that can make a damp home far more comfortable to live in. Pick a compressor model for normal heated rooms and reserve a desiccant for genuinely cold spaces, size it to the job, run it on a humidistat with the door shut, and it will cost a few tens of pounds across a winter rather than the hundreds people sometimes imagine. The one thing to stay clear-eyed about is whether you are curing the damp or only keeping it at bay, because that decides whether the running cost is a sensible expense or a bill with no end.