Pretty much all tumble driers use electricity – there are some gas-powered ones but they’re typically in launderettes and industrial facilities and we won’t cover those kinds in our comparisons because they’re too specialist.

We would advise everyone not to use a tumble dryer when the weather outside allows for washing-line drying: not only is it free, the clothes benefit from a good airing! However, there are days when this simply isn’t possible and we’ve got to turn to the machine for some help.

Tumble driers work by using warm air to absorb the moisture in clothes. To do this, they generally start with cool air, heat it up and blow it into the drum. At this point, there’s important differences in how the work.

Old style (‘Vented’)

Once the air has been passed through the drum, it’s blown down a tube (that’s usually either a flexible hose the user hangs out of an open window or custom-fitted external vent cut in the wall). This is horribly energy-inefficient because the machine is constantly heating ‘new’ air from the room and blowing it out of the back of the machine. An old kind of tumble dryer can easily cost £1.50 in electricity for a full load.

Condensing dryer

Rather than cycle the air from the room, through the machine and outside, a condensing machine uses a ‘closed loop’ of air: the warm, wet air from the drum is passed through a heat exchanger that transfers the heat to the (cooler) room air. This causes the air from the machine to cool and the water vapour condenses – forms water droplets – on the exchanger. This water is then pumped into a storage tank or, if the machine is plumbed-in, into the drain. The cooler air is then re-heated and sent back into the drum.
A condensing dryer isn’t really that much more efficient than a Vented machine – the same full load of washing will use about the same amount of energy – but because the room air isn’t being pumped outside, there’s a certain saving in not having to re-heat the air in the home.

Heat pump dryer

The pumped machine is another ‘closed circuit’ machine but the big difference is that the warm, wet air is blown over a heat exchanger that transfers the warmth into a fluid. The cooler, drier air then needs to be reheated – and this is done by moving the now warm fluid into another heat exchanger that ‘works backwards’ and transfers most of the heat in the fluid back to the air.
This is way more energy-efficient than the condensing or the vented machine because it’s reusing the heat energy rather than transferring it outside or into the room’s air. Compared to the other machines, a pumped dryer will typically use £0.60 – more than half the running cost.
Unfortunately, a pumped dryer will cost more to buy but for a family that needs to use a dryer, they are the ideal choice.