How much does a tumble dryer cost to run?

A tumble dryer is usually the most expensive appliance in a house to run per hour of use, because it does the most thermodynamically expensive thing a household appliance does: it turns liquid water into vapour. That is a fixed physical cost of roughly 0.7 kilowatt hours per litre, and the only ways to reduce it are to start with less water, to recycle the heat, or not to use the machine.

What you'll need

• Your electricity unit rate in pence per kWh
• The dryer's energy label or manual
• A plug-in energy monitor, for the real figure (optional)

Step by step

1. Find the energy per cycle.Tumble dryer energy labels quote kWh per 160 cycles, so divide the label figure by 160 for a per-cycle number on the standard cotton programme. The manual usually gives figures for other programmes and load sizes too.
2. Multiply by your unit rate.kWh × pence per kWh = pence per cycle. If a machine uses 2 kWh for a full cotton load and your rate is 25p, that load costs 50p to dry. Substitute your own two numbers; that is the whole calculation.
3. Understand the physical floor underneath it.Evaporating water takes roughly 0.7 kWh per litre in a conventional vented or condenser dryer. A heat pump machine recycles most of the heat and gets to roughly a third of that. No setting, programme or brand escapes the physics; only heat recovery does.
4. Work out how much water you are actually asking it to remove.A cotton load spun at 1400 comes out holding roughly 45 to 55 per cent of its dry weight in water; at 800 it holds about 70 per cent. On a six kilogram load that difference is well over a litre — which is close to a kilowatt hour of drying in a conventional machine.
5. Raise the spin speed first.This is the largest and cheapest saving available. Spinning water out costs almost nothing; boiling it off costs a lot. Use the highest spin the fabric tolerates on anything destined for the dryer.
6. Use sensor programmes rather than timers.A timed cycle keeps running after the load is dry, tumbling hot dry fabric in hot air at full cost and no benefit. Sensor programmes stop when the moisture reading says the job is done.
7. Fill the drum properly — two thirds, not full and not nearly empty.Cost per item drops with a fuller drum, up to the point where air can no longer move through the load. Past that point the cycle lengthens and the saving reverses.
8. Measure it, if the number matters to you.A plug-in energy monitor between the socket and the dryer gives the true consumption of your machine on your programme with your load, which no label can. It usually surprises people in one direction or the other.
9. Compare against the alternatives on the same basis.A dehumidifier running alongside an indoor airer typically draws a few hundred watts and dries a load overnight. Line drying costs nothing. Run the same arithmetic for each and the comparison becomes concrete rather than theoretical.
10. Factor in the time-of-use tariff if you have one.Because a dryer is a large, fixed, unavoidable block of energy, shifting it into a cheap window is one of the most effective single changes available on such a tariff.

Tips

• Every additional 200rpm of spin is essentially free money if you tumble dry. It costs a few seconds of motor time and removes water the dryer would otherwise have to heat.
• Dryer balls keep the load open so air moves through it, which shortens the cycle. That is a real, if modest, saving on every load.
• Drying a load that is already nearly dry costs disproportionately little; drying one that came out of a 400 spin costs disproportionately much. Sort your drying by how wet things are, not just by fabric.
• If the machine is a vented one, remember it is also blowing heated room air outside during winter, which the heating then has to replace. That cost does not appear on the dryer's label.

Common mistakes

• Multiplying the dryer's wattage by the cycle time — The heater cycles on and off under thermostat control, and a heat pump machine never draws its peak continuously. This method substantially overstates the cost.
• Using a timed programme 'to be sure' — It runs on past dry at full energy cost, and over-dries the load, which is also what causes shrinkage, static and pilling. Sensor programmes cost less and damage less.
• Comparing dryer types on purchase price alone — A heat pump machine uses roughly a third of the electricity. Over several loads a week for several years, that difference is usually larger than the price gap.

Questions people ask