closed loop · heat pump dryer · more efficient · ventless dryer · Aug 25, 2022

What is a Heat Pump Dryer? What are the pros and cons of owning one?

Living in the woods has certain advantages and disadvantages. The scenery is gorgeous and trees filtering sunlight shields my home from excessive heat in the summer, but growing vegetables and drying clothes outdoors have not been successful! When I bought my current dryer in 2017, I looked at all the available features and finally decided on a large, mid-grade version (I wanted to be able to wash and dry comforters at home instead of going to a laundromat or sending them to the cleaners). Despite its “eco” settings, I generally use the accusensor at the “most dry” setting to be sure my clothes are dry, because they often sit in the dryer for 12-24 hours afterwards due to forgetfulness…

There is a “new” kid on the dryer appliance block. I call it “new” because this type of dryer has apparently been used for a long time in Europe and other countries, but has only been in the US for less than 5 years. Heat pump dryers are one of two types of ventless dryers; the other type is condenser dryers. Of the two, heat pump dryers are the more energy efficient in terms of electric consumption and waste heat output into the laundry room.

This video is a good overview of how heat pump dryers work, and on a practical side, the video in this article shows the typical maintenance needed on a heat pump dryer.

Regular (electric or gas) dryers cause the following problems:

using a lot of energy to heat air and then immediately exhaust the heat outdoors
Drawing conditioned air from your home to run through the dryer (resulting in negative pressure and energy loss on the order of 200 cfm of conditioned air)
Release of ultra-fine particles (UFPs) into the air of your home and outdoors

The heat pump dryer may solve these problems by:

Recycling heated air instead of dumping it
Causing little-no air draw from the rest of your home
No dryer vent means no dusty air leaks inside, or dumping UFPs outside.

Pros:

Operating cost is at least 28% less (energystar.gov) and can be up to 50% less than regular vented dryers (nytimes.com).
Owners of more energy-efficient homes will appreciate that a heat pump dryer will not try to pull a negative pressure by dumping conditioned air through the vent.
Some models operate on 120v (Miele at least), which make them more versatile.
No vent needs to be installed! They can be installed in very small spaces and operate well no matter what temperature or humidity conditions are present in the house.
Heat pump dryers are better at fabric care because the dryer temperature is typically lower than conventional dryers (greenbuildingcanada.ca)

Cons:

Not all heat pump dryers perform the same. This review of the Whirlpool YWED7990FW in 2019 claimed that it significantly raised the temperature and humidity of the small laundry room and surrounding area, and took significantly longer to dry, but a respondent claimed that his Miele dryer (a widely known German manufacturer) only raised the temp by a few degrees with the same drying time as a conventional dryer. Another owner of a Whirlpool WED99HEDW was quite happy with his purchase after 4 years.
More maintenance is needed to keep the heat pump dryer working efficiently; a vacuum with soft head may be needed to clean the heat exchanger coils every so often, and it may need professional deep cleaning to remove lint deep inside the machine every few years.
Some heat pump dryers need to be installed near a drain, to dispose of condensed water from the clothing. Others have reservoirs that can be emptied every so often.
Heat pump dryers are still relatively uncommon, so if the unit does need servicing, it may be difficult to find a knowledgeable technician if you live outside a major metro area.
There is a higher upfront cost for heat pump dryers vs. conventional dryers
Drum capacity is typically smaller (greenbuildingcanada.ca)

You can find some 2022 reviews for heat pump dryers here, which are compact (the review is for compact washers and dryers, and most compact dryers are ventless). Is a heat pump dryer right for you and your family? Here are two major topics for your consideration:

Financial standpoint: Heat pump dryers cost more upfront, typically from between $800-$1400. However, they save money each load in operating cost, and they save money by not pulling unconditioned air into your home throughout the load. Let’s breakdown the costs and savings.

Here is a page I used to calculate how much it costs to operate my conventional electric dryer per load:

My electric cost is about 10 cents per KW (from my electric bill). My dryer uses 6240 watts (26 amps x 240 volts) per hour. One cycle takes about 45 minutes (0.75 hour), so cost per cycle is 0.10 x 6240 x 0.75 / 1000 = 47 cents per load.

If I purchased a heat pump dryer and it gave me the minimum 28% energy savings, then operating the dryer would cost 34 cents per load (47 x 72%).
I do about 5 loads of laundry per week, so using a heat pump dryer may save me about $34 per year (0.13 x 5 x 52).
These savings translate to approx. 3 years payback time for every $100 more that a heat pump dryer may cost over my current dryer. HOWEVER, more savings come in when you consider the conditioned air you are not exhausting through your dryer vent:
HVAC rule of thumb: there is approx 400 cfm per ton of cooling power, and 12,000 BTU/hr (British Thermal Units). My AC unit is 3.5 tons, so this would be 1400 cfm and 42000 BTU/hr when the AC is running. (learnmetrics.com) Typical electric dryers suck 200 cfm of conditioned air out of the house while running. That’s how much cfm we’re losing, so let’s translate that into a cost. This article tells me (in table 3) it costs $0.56 per hour to run a 3.5 ton unit (halfway between a 3 ton and a 4 ton unit), for the average US electric cost of $0.1319/kwh. I’m going to ratio that down to my electricity cost of $0.10 per kwh, which would be $0.42/kwh to run my 3.5 ton unit. If I lose 200 cfm from the dryer, then over 45 minutes this is 9000 cubic feet of conditioned air. 9000 cf/1400 cfm = run time of 6.4 minutes to make it up, which at a cost of $0.42/hr = $0.045 extra. If I run my heater or AC 8 out of 12 months, this is 67% of the year, so we’ll multiply the 4.5 cents by 0.67 to get 3 cents per load. The real cost to run my regular electric dryer is 47 cents per load (calculated above) plus 3 cents per load due to excess heating/cooling costs, or 50 cents per load. The adjusted savings for using a heat pump dryer is ($0.50-0.34)x 5 loads a week x 52 weeks a year, which is about $42/year. This gets me to about a 2.4 year payback for every $100 over regular dryer cost all because the dryer is pulling all kinds of hot and humid air into my house in the summer, or cold damp air into the house during the winter. Honestly, in a humid environment like the southeast US, I think the actual cost is higher because of the latent heat (humidity) that the AC unit struggles to remove from the air.

Air Quality standpoint: The nature of ultra-fine particles allows them not only to penetrate the air barrier of most homes, it also allows them to penetrate deep into your lungs and into your bloodstream. Broadcasting UFPs into the outside air via the dryer exhaust allows some of them to come back into your home through air leaks (because conventional dryers pull a negative pressure on your laundry room, if not your home), and if your dryer vent line has any leaks, they are coming into your laundry room in a more direct route anyway. With a heat pump dryer, the air is moving in a closed loop through a filter, which is cleaned in the same way as a conventional dryer filter, but the rest of the UFPs are pulled out of the airstream via condensed water. The good thing is that the UFPs going into the condensed water are not being broadcasted into the air to cause respiratory issues. The other good thing is that pollen and pollution outside is not being sucked into the home by the negative pressure that regular dryers generate.

The issue that is not addressed by most dryer manufacturers is how UFPs are captured in the condensate drain line. If your new heat pump dryer has a reservoir, then emptying the condensate through a filter is easy. If it drains into a plumbed drain, you may want to invest in a drain filter (there are a variety of drain filters designed for washing machines that would work fine, especially since the dryer will produce a lot less condensate than a washing machine drain). Here are some options:

PlanetCare Microfiber filter by Celsious ($98) is a top pick because it allows you to customize your drainhose size and will soon offer recycling of the filter cartridges.
If you have a reservoir type machine, you can pour the accumulated condensate through a coffee filter to any drain, and toss the coffee filter.
There are many other solutions that can be adapted to filtering drier condensate by searching “washing machine microfiber filter”.

The bottom line is that heat pumps and dryer electronics continue to improve every year. Although many brands and models did not have great reviews in 2019, they look much better 3 years later. If you are fastidious about building and keeping the best air quality in your home, a heat pump dryer should be something you consider the next time you need to purchase a dryer!

Photo by Raychan on Unsplash

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