Heat dryer: the way it works

When it comes to eco-friendly and energy-efficient housekeeping, heat pump dryers are often at the top of the list of desired equipment. How such a heat pump dryer works, which forms the technical basis of this technology and where the advantages and disadvantages of heat pump dryers are revealed in this article.

heat pump principle

Heat pumps generally work like a refrigerator - just the other way round. Conversely, when air or water is removed from the heat by a coolant, this heat can be reused for heating.

Even a refrigerator produces waste heat - this is exactly the heat that it extracts from the food that is in it. Theoretically, you could also use a refrigerator for heating - some food markets do exactly that with their cooling systems.

Conversely, you can use the heat contained in the ambient air to heat a house. If the heat is removed from the air by a refrigerant, this heat is again available for heating.

Application of the heat pump principle in the heat pump dryer

Clothes dryers operate on the physical principle that warm air can absorb more moisture than cold air.

So if the air inside the heat pump dryer is heated, it absorbs a part of the moisture of the cold, wet laundry, much like a hair dryer by blowing hot air over it dries the hair.

However, heating air costs a lot of energy. In the heat pump dryer, therefore, the exhaust air is passed through a heat pump. The heat is removed from the exhaust air, and used again to heat the cold supply air of the unit.

This creates a cycle in which the heat once generated is used again and again. This considerably reduces energy consumption.


Upon cooling, the moisture contained in the air that has been absorbed by the laundry condenses. Since cold air can store less moisture than warm air, the air contained condenses on cooling as condensate.

This condensate is collected in a condensate tank. After that, it can easily be disposed of or pumped out.

Condensation is even faster with the heat pump dryer than with conventional condensate dryers, because the air is cooled down very quickly via the heat pump. The warm exhaust air is removed by the coolant immediately all heat to supply the supply air as completely as possible again.

However, the device does not have a shorter operating time compared to conventional condensation tumble dryers.

Energy efficiency and cost-benefit ratio of heat pump dryers

According to the results of a study by Stiftung Warentest, heat pump dryers usually require about half the energy that conventional dryers consume. On average, according to the findings of Stiftung Warentest, a dryer load costs about 1 EUR for a conventional appliance, but only 40 cents for the heat pump dryer.

But the acquisition costs are also significantly higher. However, the purchase price has already declined significantly in recent years - the higher initial costs are quickly paid off entirely by the lower electricity consumption for families and multi-person households.

Of course, the higher the energy rating of the device, the greater the difference and the better the cost-benefit calculation.

When considering a purchase, one should also consider the development of the price of electricity in the coming years. Individual forecasts predict further increases in electricity prices of up to 40 cents / kWh by the year 2020.

Disadvantages of heat pump dryers

Technically, there are no disadvantages of heat pump dryers compared to conventional devices. So far, only the higher initial costs have a negative effect, which does not pay off in all cases (single household, rare use).

For most devices that work on the heat pump principle, you have to expect slightly longer drying times. The fact that no heating element is used, the drying time can be extended in some cases up to two or three hours.

Advantage: Laundry-friendly drying

But - thanks to the lower use of hot air - also the fabric of the laundry is spared in comparison to conventional dryers. The service life of the clothing is thus extended rather than the frequent use of conventional dryers, they usually more or less significantly shortened.

Heat pump dryer Purchase advice

When selecting the units, both the filling quantity and the energy efficiency class should be the decisive criterion - in conjunction with the purchase price, of course. Branded devices are often more durable and energy efficient than no-name devices. But this does not have to apply in all cases.

In any case, before purchasing a cost-benefit calculation to see whether the purchase is even worthwhile for you, and if so, up to which price.

Tips & Tricks

Of course, it is the most ecological and energy efficient to dry the laundry on a leash or in a drying room. Often it's just a matter of spending time and planning to save a lot of energy here.

If you only have a few items of laundry and want to speed up drying, you can put the wet laundry on a microfiber towel as big as possible. Then roll in the towel as tight as you can. In this way, a large part of the moisture is already squeezed out of the laundry. A good microfibre towel is completely dry after just a few minutes.

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