Dehumidifier running cost calculator
Dehumidifiers have a reputation for being expensive to run that most of them do not deserve. Put in your machine and your unit rate and this works out what it actually adds to the bill, per hour, per day, per month and across a winter.
Check your bill. The default is the Ofgem cap rate for 1 July to 30 September 2026.
Most UK households only need one through the damp season, roughly October to March. That is about 180 days.
Cost per month while you are using it
£7.54
216W drawing 0.95 kWh a day, at 26.11p per kWh. Based on 8 hours switched on and about 55% of the hours spent actually running.
Per hour running
5.6p
Per day
24.8p
Per year (180 days)
£44.67
What this is based on
- A default unit rate of 26.11p per kWh, the Ofgem price cap rate for a direct debit customer on a standard variable tariff, 1 July to 30 September 2026. The cap changes quarterly, so the field is editable.
- No standing charge. That is a fixed daily cost you pay whether the dehumidifier is plugged in or not, so adding it here would overstate what the machine costs you.
- Typical draws of 165W for a 10L to 12L compressor machine, 216W for a 20L compressor machine at 20C and 60% relative humidity, and 500W for a domestic desiccant model. Manufacturers quote at their own test conditions and real draw varies with room temperature.
- Humidistat mode assumed to run about 55% of the time it is switched on, once the room has reached its target. A cold, wet room will sit closer to continuous until it dries out.
- A month taken as 30.4 days.
Figures reviewed 17 August 2026.
What a dehumidifier really costs
The maths is the easy part. Power in kilowatts, multiplied by hours, multiplied by your unit rate. A 216W machine is 0.216kW, so eight hours is 1.73 kWh, and at 26.11p that is about 45p. The reason people get wildly different answers is that almost nobody knows which of those three numbers applies to them.
The wattage on the box is often a peak figure measured in conditions your bedroom will never see. The hours you think it runs and the hours it actually runs are different numbers if it has a humidistat. And the unit rate people quote is usually whatever the news said the price cap was, which is not what you pay if you are on a fixed tariff.
Set against that, here is the number that matters most: a compressor dehumidifier draws roughly a tenth of what a 2kW electric heater draws. Running one for eight hours costs about what the heater costs in fifty minutes. Anyone who tells you a dehumidifier is expensive to run is comparing it to nothing at all, rather than to the alternatives.
Compressor against desiccant
There are two technologies on the shelf and they are not interchangeable, which is where most of the money gets wasted.
A compressor machine, sometimes labelled refrigerant, chills a coil so moisture in the air condenses onto it and drips into the tank. It is the same principle as a fridge, and it has the same weakness: it needs a reasonably warm room to work. Below about 15C the coil starts icing up and the machine spends its time defrosting itself instead of collecting water. In a heated house it is comfortably the cheaper option at 150W to 350W.
A desiccant machine passes air over a moisture-absorbing wheel and uses a heater to drive the water back off it. That heater is why it draws 500W and up, and also why it works fine at 5C. If the problem room is a garage, a loft, a conservatory or an unheated back bedroom, the desiccant is the one that will actually do something, and the extra running cost is the price of it working at all. It also blows out warm air, which in a small room is not entirely a downside.
Buy the compressor for a heated home. Buy the desiccant for a cold space. Buying the wrong one costs you either the purchase price or three times the electricity.
What size dehumidifier do I need?
Dehumidifier capacity is quoted in litres of water extracted per day, measured in laboratory conditions that your house will not reproduce. Treat the number as a relative scale rather than a promise.
- 10L a day. One or two bedroom flat, mild condensation on windows in the morning, one problem room.
- 12L to 16L a day. Two or three bedroom house, condensation in more than one room, or a household that dries washing indoors.
- 20L a day and up. Four or five bedrooms, an established damp problem, visible mould in more than one room, or a house you are trying to dry out after a leak.
Undersizing is the mistake that costs money, which is counterintuitive. A machine too small for the space never reaches its target humidity, so it runs flat out permanently. A larger machine reaches 50% and switches off. The bigger unit has a higher wattage but spends most of the day idle, and the annual bill comes out lower.
One other thing worth knowing before you buy: the tank size determines how often you empty it, not how well it works. A 20L-a-day machine with a 3L tank in a genuinely damp house needs emptying more than once a day. Most units take a continuous drain hose, and running one to a sink or an outside drain turns the whole thing into something you do not have to think about.
Getting the cost down without turning it off
Almost every saving available comes from the humidistat, and most people never touch it.
A dehumidifier with no humidistat, or with the dial turned to maximum, runs continuously whenever it has power. Set to a target of around 50% relative humidity, it runs until the room gets there and then cycles off, restarting only when humidity climbs again. In a house that is not soaking wet, that roughly halves the running hours, and the room is no damper for it. Our calculator above shows both figures side by side, and the gap is usually the difference between complaining about the running cost and not noticing it.
Beyond that:
- Shut the door. Dehumidifying one room with the door open means dehumidifying the house, and the house includes the bathroom you keep refilling with steam.
- Aim for 45% to 55%, not the lowest number on the dial. Mould needs sustained surface humidity above roughly 80% to get established. Holding a room at 50% keeps even the cold wall behind the wardrobe well clear of that. Going lower costs money and dries out timber and skin for no benefit.
- Use it where the washing is. A load of wet laundry puts around two litres of water into the air. Drying it in one room with the door shut and the machine running is dramatically cheaper than a tumble dryer and stops the moisture ending up condensing on your bedroom wall.
- Give it room to breathe. Air has to get in and out. Pushed into a corner against the curtains, it works against itself.
- Run it on a timer overnight if you are on an Economy 7 or off-peak tariff. The unit rate in those hours can be less than half the day rate, which changes the sums entirely. Put your actual off-peak rate into the calculator and see.
Where a dehumidifier is the wrong answer
A dehumidifier deals with one thing: too much water vapour in the air inside your home. Condensation, in other words. If your windows stream in the morning, if mould grows in corners, behind furniture and on cold outside walls, if the bathroom never seems to dry out, then a dehumidifier is a genuinely effective and cheap intervention.
It does nothing at all about water arriving from outside. A leaking gutter dumping water down a wall, a failed damp-proof course drawing moisture up from the ground, a cracked render letting driving rain through, a slipped tile: for all of those, a dehumidifier is an expensive way of not fixing the problem. It will lower the humidity slightly and the wall will keep getting wet.
Telling the two apart matters, because the fix and the cost are completely different. Condensation appears on cold surfaces, worst in winter, worst in unheated rooms, and worst where furniture blocks air movement. Penetrating and rising damp appear as tide marks, blown plaster and salt deposits, they are often worse after rain, and they do not care what the humidity in the room is. If you have taken moisture readings, or a surveyor has, run them through the damp meter reading checker before you accept anyone's diagnosis. And if you want an independent opinion rather than one from a company selling the treatment, the damp survey cost calculator covers what that should cost.
Where mould is already established, drying the air stops it spreading but does not remove it. That is a cleaning job at best and a remediation job at worst, and the mould removal cost calculator covers where the line between the two sits. If you are renting and the damp is the property's fault rather than yours, the electricity you have been burning on a dehumidifier is a recoverable cost in a disrepair claim, which the compensation calculator accounts for.
Dehumidifier running costs: common questions
How much does it cost to run a dehumidifier in the UK?
A typical 20L compressor dehumidifier drawing 216W costs about 5.6p an hour at the July 2026 price cap rate of 26.11p per kWh. Run for eight hours a day that is roughly 45p a day, £13.60 a month, or £164 a year if you ran it every day. A desiccant machine at 500W costs about 13p an hour, so nearer £1.05 a day and £31 a month on the same eight hours.
Are dehumidifiers expensive to run?
Compared to heating, no. A 216W dehumidifier uses about a tenth of the electricity of a 2kW fan heater, and because dry air feels warmer than damp air at the same temperature, running one often lets you drop the thermostat. Compared to opening a window, it is obviously not free. The honest answer is that a compressor machine on a humidistat costs most households between £10 and £20 a month through the damp season.
Do dehumidifiers use a lot of electricity?
Less than most people assume. Most domestic machines draw between 150W and 350W, which is comparable to a large television and considerably less than a kettle, an oven or any form of electric heating. Desiccant models are the exception at 500W to 900W, because they work by heating the air rather than chilling it.
What size dehumidifier do I need?
As a rough guide: 10L a day suits a one or two bedroom flat with mild condensation, 12L to 16L a three bedroom house, and 20L or more a four or five bedroom house or any property with a real damp problem. Undersizing is the common mistake, because a machine that has to run flat out permanently costs more to run than a larger one that cycles off.
Is it cheaper to run a dehumidifier or the heating?
A dehumidifier, by a wide margin, if the goal is dealing with condensation rather than being warm. A 216W dehumidifier costs about 5.6p an hour against roughly 52p an hour for a 2kW electric heater. They do different jobs though, and in a cold room a compressor dehumidifier struggles because there is not enough heat for the coil to condense water out of the air. Below about 15C, a desiccant model is the one that works.
Should I leave a dehumidifier on all the time?
Use the humidistat rather than the switch. Set it to somewhere between 45% and 55% relative humidity and leave it to cycle. Mould needs sustained surface humidity above roughly 80% to establish, and holding a room at 50% keeps every surface comfortably clear of that even when the wall behind the wardrobe is colder than the air. Running continuously at maximum costs nearly twice as much and dries the air past the point of any benefit.
Will a dehumidifier get rid of my mould?
It stops it spreading and stops it coming back, but it does not remove what is already growing, and it will not fix damp coming through a wall from outside. A dehumidifier is the right answer to condensation. It is the wrong answer to a leaking gutter, a failed damp-proof course or penetrating damp, where all you are doing is paying electricity to manage a symptom.