Tumble Dryers, Heat Pump Dryers and Line Drying

Why drying matters

Of the main laundry steps, drying by machine is typically the most energy-hungry. Warming air to evaporate water from a full drum takes a lot of heat, and unlike a washing machine, which mostly heats water, a dryer has to heat air continuously and push moisture out. For that reason, it is usually worth thinking about how you dry clothes at least as much as how you wash them.

There are three broad approaches, and most households end up using more than one.

Line drying and airers

Drying outdoors on a line or a rack uses no energy beyond the effort of hanging out the washing, and it is the lowest-impact option when the weather allows. Wind and sun help, and many people find clothes smell fresh. The limits are practical:

• Weather, daylight and space can all get in the way.
• Pollen and air pollution can be a problem for people with allergies.
• Some fabrics may fade in strong sun, and some towels feel stiff after air drying.
• Some leases, housing associations or community rules restrict outdoor lines, which is something tenants may want to check. Renting sustainably often involves this sort of compromise.

Standard tumble dryers

There are two main kinds of conventional dryer:

• Vented dryers blow warm moist air outside through a hose. They are simple and usually cheaper to buy, but they need a place to vent and they send warm air out of the home.
• Condenser dryers cool the moist air to collect water in a tank or drain it away, then reheat and recirculate the air. They need no vent, although they release heat and some moisture into the room.

Both typically use a lot of electricity or gas per load, and they tend to cost more to run than line drying, which costs nothing.

Heat pump dryers

A heat pump dryer works differently. It recycles heat from the exhaust air instead of venting it, using the same basic principle as heat pumps used in homes. Because it moves and reuses heat instead of creating all of it from scratch, it generally uses noticeably less energy than a standard electric dryer for the same load. The trade-offs are:

• A higher purchase price than most conventional dryers.
• Longer cycle times, since the drying temperature is lower.
• Some are sensitive to very cold or very hot rooms.
• Filters and heat exchangers need cleaning regularly so they keep working properly.

Whether the energy saving justifies the extra cost depends on how often you dry clothes and local energy prices. For a household that dries a lot of laundry, it may pay off over time. For one that dries a little, it may not. Energy labels let you compare models, and it is worth bearing in mind that manufacturing a new appliance has its own footprint, so replacing a working dryer is not always the lowest-impact choice.

Making any method work better

• Spin faster before drying. A higher spin speed removes more water mechanically, which tends to cut drying time. Check the care label first, as delicate items need gentle spin.
• Do not overload. Clothes need room to tumble, and overpacking can lengthen cycles.
• Clean the lint filter every time. A clogged filter makes the machine work harder, and lint is also a fire risk. Follow your manual for deeper cleaning of condensers and heat exchangers.
• Mix loads sensibly. Drying similar fabrics together avoids over-drying some items while others stay damp.
• Use sensor programmes where available, as they stop when clothes are dry instead of running to a fixed time, and avoid extra-hot settings unless needed.
• Avoid over-drying. Items left in a hot drum can wear faster and may shrink.

Drying indoors: the practical limits

Indoor drying on racks or radiators avoids running a dryer, but it adds moisture to the home. A load of washing contains a significant amount of water, and all of it ends up in the air if the clothes dry indoors. In poorly ventilated rooms this can contribute to damp, condensation and mould, which are not good for the building or for some people’s health.

Some ways of limiting problems include:

1. Dry clothes in a room that you can ventilate, with a window open or an extractor fan running if you have one.
2. Keep doors closed to the rest of the home so moisture does not spread.
3. Avoid draping wet clothes over active radiators in ways that block heat, and do not cover heaters.
4. Consider a dehumidifier in a small closed room, remembering that it uses electricity too.
5. Watch for signs of trouble such as streaming windows, musty smells and mould. Our guide on condensation control goes into the wider causes and fixes.

Good ventilation also supports indoor air quality, which is worth thinking about in smaller or well-sealed homes. If you have asthma or other respiratory conditions, or you are concerned about mould, talk to a health professional or your landlord rather than relying on general advice.

Choosing a mix

For most households there is no single best option. A common pattern is to line dry when the weather suits, use an airer in a ventilated room for part of the year, and keep a dryer for towels, bedding or wet spells. If you are buying a dryer, a heat pump model is a good candidate where it fits your budget and use, but using it less and using it well tends to matter more than the technology alone.