Why is a washer-dryer so expensive to run?
Compare what a tumble dryer, heat pump dryer, heated airer, dehumidifier or an ordinary clothes horse costs per load — and how much water each one leaves in your home.
Using the Belgian average of 34.99c/kWh — Eurostat, the second half of 2025.
The most expensive way to dry washing in this list, for a reason built into how the machine works. Note the smaller load: a washer-dryer dries about half what it washes, so this is the realistic cycle rather than the full 7 kg used on the other pages — compare it on cost per litre, not cost per load.
Common cases
What drives the cost
The washer-dryer is the most expensive way to dry a load on this page, and the reason is structural rather than a fault in any particular machine. Most models condense the moist air using cold mains water rather than a separate air condenser or a heat pump. That works, but it throws the heat away entirely and consumes water while doing so — which is why a drying cycle in one can cost three to four times a heat pump dryer for the same washing.
There is a second, sneakier cost. A washer-dryer almost always dries a smaller load than it washes, often half. So a full wash becomes two drying cycles, and the per-load figure above quietly doubles in practice. None of this makes them a bad purchase — in a flat with no room for two machines and no outside space, the alternative is not a better dryer but no dryer at all. It just means the convenience is bought at a running cost worth knowing before you rely on it daily.
How this is worked out
Drying is evaporating water, so the honest unit is not watts but energy per litre removed. A load of washing leaves the machine holding three to four litres, and every method here is doing the same job: getting that to zero. Evaporating a litre and letting the vapour drift away costs about 0.66 kWh, which sets a hard ceiling of roughly 1.5 litres per kilowatt hour for anything that just blows warm air at wet cloth. A heat pump dryer and a dehumidifier beat that ceiling, and they are not cheating: they condense the vapour back into water, which releases that same latent heat, and they reuse it. It is exactly the trick that lets a heat pump heat a room for a third of the electricity.
What this assumes
- Water left after the spin is taken as a share of the clothes' dry weight: 80% at 600 rpm, 70% at 800, 60% at 1000, 54% at 1200, 50% at 1400 and 46% at 1600. These are representative of EU spin-drying classes measured under EN 60456 — 50% at 1400 rpm sits in class B. Real machines vary by several points either way, and the relationship is logarithmic, so doubling the speed does not halve what is left.
- Litres removed per kilowatt hour, by method: heat pump dryer 2.4, dehumidifier 1.8, vented dryer 1.05, condenser dryer 1.0, heated airer 1.0, washer-dryer 0.6. An ordinary airer indoors is priced at the physical limit of 1.5, because the water is evaporated by heat your heating system then has to replace.
- The dehumidifier figure is deliberately below its nameplate. Those are measured at 30 °C and 80% humidity, which no room is, but a closed room with wet washing in it is far more humid than an ordinary one — so real performance sits above a cold-room figure and below the label.
- Drying indoors on an unheated airer is costed as electricity, since that is what this site prices. If your heating is gas, the same heat costs perhaps a third as much, so treat that row as the upper bound. If the heating is off entirely, the washing takes days and the whole cost lands on the house instead as damp.
- Nothing here counts the machine's own motor, controls or the water pumped away, all of which are small next to the evaporation. Nor does it count buying the appliance, which for a heat pump dryer is the number that actually decides the question.
- Tumble dryer figures assume drying to cupboard-dry from a normal spin. Drying a half-empty drum, or over-drying on a timer rather than a sensor programme, both cost noticeably more than this.
- The rate filled in for you is an average that spreads fixed charges across a year's usage, so it sits above what one extra unit really costs. Entering the unit rate from your own bill gives a closer answer.
Questions
Why can't I dry a full wash load in my washer-dryer?
Because clothes need room to tumble through moving air to dry, and a drum sized for washing is too full to allow that once the same load is being dried. Manufacturers state a drying capacity roughly half the washing capacity for this reason. Overloading it does not break anything, it just makes the cycle run far longer for a worse result.
Is a separate washer and dryer cheaper overall?
On running cost, comfortably — especially if the dryer is a heat pump model. On purchase price and floor space, no. The honest comparison is not machine against machine but what your home allows: if there is room and a plumbing point for two, separates win on cost per load by a wide margin.
What is the cheapest way to dry clothes?
Outdoors, and it is not close — a washing line costs nothing and puts no water in your house. Of the powered methods, a heat pump tumble dryer is cheapest per load, at roughly a third of an ordinary vented dryer. A dehumidifier in a closed room comes next and has the advantage of collecting the water rather than leaving it in your walls. The most expensive is the drying cycle on a washer-dryer, which can cost three or four times a heat pump dryer for the same load.
Is drying clothes indoors really free?
No, and the cost lands in two places. The water has to be evaporated by something, and if your heating is on, that something is your heating — about 0.66 kWh per litre, so two to three kilowatt hours for a typical load. Then the water itself, three to four litres, is now in the air of your home, and it condenses on the coldest surfaces it can find. That is where the wet windows, the black corners and eventually the mould come from. It is the cheapest indoor method on electricity and the most expensive on damage.
Does spinning at a higher speed save money?
More than any other single change here. Spinning is mechanical and cheap; evaporating is thermal and expensive. Going from 1000 rpm to 1600 rpm cuts the water left in the load from 60% of its dry weight to 46% — nearly a quarter less to dry, for a few extra minutes of a motor that was running anyway. If you take one thing from this page, spin faster before you dry.
Are heat pump tumble dryers worth the extra money?
On running cost, clearly: roughly a third of a conventional dryer, so a household drying several loads a week saves a meaningful amount every year. The catch is the purchase price, typically a few hundred more, and the cycle takes longer because it runs cooler. Whether it pays back depends almost entirely on how many loads you actually dry — a family drying eight loads a week gets there in a few years, someone using a dryer occasionally in winter does not.
Is a dehumidifier cheaper than a tumble dryer?
Cheaper than a vented or condenser dryer, yes, and comparable to simply hanging the washing in a heated room. Its real advantage is different: it collects the water in a tank instead of releasing it into your home, so it dries the laundry and protects the building at the same time. It is slower than a dryer, needs the door shut to work properly, and the electricity it uses ends up as heat in that room, which in winter is not wasted.
Why is my washer-dryer so expensive to run?
Because of how it condenses. Most washer-dryers cool the moist air using cold mains water rather than a separate condenser or a heat pump, so they throw away the heat and use water doing it. They also dry a smaller load than they wash, which often means splitting a wash into two drying cycles. Convenient in a small flat, expensive per load, and the compromise is built into the design rather than being a fault.
Should I dry clothes on the radiator?
It is the worst version of drying indoors. All the water still goes into the room, and draping wet washing over a radiator blocks the convection it relies on, so the room heats less well while the thermostat keeps the boiler running. If you must dry indoors, use an airer in the smallest room you can, shut the door, and either open a window or run a dehumidifier in there.
Related tools
- Why do my windows get wet, and will mould grow? Work out the dew point in a room, whether a cold window or wall will run with water, and the humidity you need to stay below to keep it dry.
- How much does it cost to run an appliance? Work out what any appliance costs to run per use, per month and per year on your own electricity rate — including what it draws on standby.
Sources
- IEC/EN 60456 — clothes washing machines, measurement of performance (residual moisture) — checked 2026-08-27
- Purdue — review of heat pump tumble clothes dryer energy efficiency and moisture extraction rates — checked 2026-08-27
- Engineering ToolBox — latent heat of vaporisation of water by temperature — checked 2026-08-27
Rates from Eurostat for the second half of 2025. Last reviewed 27 August 2026.