Heat Pump Dryer FAQ

Basics

Wet clothes are tumbled in a revolving drum while warm dry air from outside is passed over the clothes. The moisture evaporating from the clothes is vented out of the house as humid air through an exhaust tube. The air is warmed either by a gas flame in a gas dryer or an electric heating coil in an electric dryer.

A ventless or condensing dryer works by heating air, blowing it into the drum chamber and then pulling that warm moist air from the drum and cooling it to the point that the moisture condenses and drips into a collection tray. The cool dry air is then heated and recirculated back into the drum where it again picks up moisture and the cycle continues. This is useful in situations where installing an exhaust vent to the outside is not a feasible option.

A heat-pump dryer is a kind of condensing dryer. Like pretty much every heat pump device, the heat pump in a heat pump clothes dryer has a cold coil and a hot coil. This works out perfectly for a condensing dryer as the cold coil can be used to cool the warm moist air coming from the drum (and to provide a condensing surface for the moisture in the air) and the hot coil can be used to heat the air before sending it back. Because it successfully recirculates a part of the heat that would otherwise be vented out in a traditional clothes dryer, heat pump clothes dryers use 40% to 50% as much electricity as a traditional electric dryer and dry clothes much faster than condensing dryers that don’t use heat pumps. However the drying is about 50% slower than a traditional vented electric dryer.

Some manufacturers like LG do market a hybrid dryer where the heat pump is optional and the consumer can choose to bypass it with conventional drying if faster drying is needed. Such hybrid heat pump dryers can be vented but most heat pump dryers are ventless.

Various capacity heat pump dryers are available but the most popular ones come in two sizes – a smaller 3-4 cu ft capacity and a larger 7-8 cu ft capacity.

Economics

Usually heat pump dryers are about 50% more expensive than traditional comparable electric dryers.

Since they use about half the energy to dry, the running costs are lower but there is an extra upfront cost and unless a household uses a lot of drying throughout the year it is difficult to recoup the initial extra cost. Typical usage results is 200-300 kWh savings in energy over a year which is around $20-$50 savings depending on the cost of electricity used. The payback for the smaller capacity heat pump dryers is a little better.

Maintenance

Other than cleaning the primary lint filter as in traditional dryers, there is a secondary lint filter in these dryers which needs cleaning. On top of that sometimes lint accumulates on the condensing coils and the dryer has to be serviced to clean that.

This is a new technology and so long term reliability data is still unavailable. The manufacturer’s warranty is similar to traditional dryers. However, since the design is more complicated and more parts are involved than a traditional electric dryer, that will have some adverse effect on the long term reliability. Whether it is significant remains to be seen.

Environment

Obviously using less electricity is better for the environment especially if the electricity used is not zero-carbon.

Steps to use

There is an extra condensate drain pipe which needs to be plumbed. Other than that it is similar to a traditional electric dryer. For ventless dryers no outside venting duct is needed.

Yes, stackable heat pump dryer and washer models are available.

The heat pump dryers use much lower heat but take almost twice as long to dry than a traditional dryer. The lower heat is beneficial to clothing but the longer tumbling adds more wear and tear. So there are some pros and cons.

So far there have been no safety concerns reported for using heat pump or ventless dryers.