Climate change has the odd effect of making many of us inordinately excited about appliances we never used to care about. Suddenly, all the background machines, which have up to now been unconsciously powering our lives, have taken on outsized importance. Some of them have the potential to provide the essential services we depend on while, at the same time, not destroying our planet like the fossil fuel powered machines of the 19th and 20th centuries.
Ductless heat pumps are a prime example. In the past, many of us used gas furnaces and boilers to heat our homes and burned fuels that emitted copious amounts of CO2 in the process. Now, with the magical heat pump, we have access to efficient electric technologies for heating and cooling that can be powered entirely by renewable energy, and thus be carbon neutral.
Brief History and Growth of Ductless Heat Pumps
Ductless heat pumps (DHPs) were developed in Japan after World War 2. They were invented and perfected on an island that doesn’t have easy access to fossil fuels, and so they are the ideal heating/cooling system for our modern world given they don’t rely on combustion and are also incredibly efficient.
They condition 90% of Japanese homes, and worldwide their usage is growing like crazy, with an expected doubling of heat pump sales in the next five years. In the UK, sales are projected to increase 20 fold, and in the US, some areas are seeing sales growth north of 40% every year.
My family has used ductless heat pumps for our heating and cooling since 2012 when we bought our house. The gas furnace that came with our house was old, and we made the decision to replace it with new ductless heat pumps. (A major perk is that mounting the units on the wall saved valuable floor space in the garage, formerly dedicated to the gas furnace, which we converted into an apartment). We had seen them used in Europe and figured, even 9 years ago when the electrification movement was in its infancy, that heating with efficient electricity would allow us to reduce our carbon emissions with the solar panels we planned to install on our roof.
What is Ductless?
But what is a Ductless Heat Pump (a.k.a. mini-split)? Basically, it is a heating/cooling system that is different from a traditional furnace in several ways:
1. DHPs don’t have air ducts. Rather than forcing hot air through potentially leaky ducts, ductless systems place an indoor device on a wall and an outdoor unit (similar to a typical AC unit) which provides heating and cooling. This means no air escapes through leaky ducts, creating more efficient conditioning.
2. DHPs don’t burn things. Ductless heat pumps use electricity to provide heating and cooling. Electricity is rapidly moving towards being fully renewable and thus will soon produce zero emissions (the Biden administration set a goal of 2035 for example).
3. DHPs are like refrigerators in reverse. Instead of burning fuel, ductless heat pumps create heating and cooling through refrigeration. This means they capture heat from outside (even when it’s cold) and move it into your house, and vice versa for cooling. It’s pretty magical. The refrigerants used by DHPs can be potent greenhouse gases themselves, but luckily the world is moving quickly to using better, more environmentally friendly refrigerants (check out this website for a new type of refrigerant called R32).
4. DHPs are incredibly efficient. This is because a) no air leaks through ducts b) they heat the room they are in (rather than the whole house), c) moving heat is vastly more efficient than creating it, and d) they use inverter systems (see below). As a result, they typically use three times less energy than old electric resistance heaters and six times less than gas.
Demystifying a couple DHP terms
Speaking of efficiency, let’s demystify a couple of terms associated with ductless heat pumps.
SEER — SEER is a number that measures how well a technology provides cooling. The higher the number, the more efficient the unit. Most new air conditioners have a SEER between 13 and 21, but ductless can often see a SEER over 30, which gives you an idea of how efficient they are. If you’re in a warm climate, SEER is especially important.
HSPF — HSPF stands for Heating Season Performance Factor and complements the SEER rating in that it measures how efficiently a heat pump heats a space. The minimum required HSPF rating in the US is 7.7. An 8.5 score is considered good, and over 10 is excellent. If you’re in a cooler climate, where the predominant energy use is for heating, HSPF is most important.
I interviewed Tim Sharp, from the Heat Pump Store here in Oregon, which has installed thousands of ductless heat pumps over the last decade. He said that you’ll want your DHP to be most efficient in heating if you’re in a cold climate, and cooling if you’re in a warm climate. People in the northern US should probably focus on HSPF, while in the southern US, people should focus on SEER. Tim also said that investing in a DHP with higher scores will be more expensive up front, but the additional cost usually pays for itself over time through energy savings.
Ductless Heat Pumps in Cold weather
I also learned from Tim that DHPs were originally developed to provide only cooling (like a refrigerator), yet they have “constantly gotten better for heating purposes in almost every environment.” If you’re in a cold climate, you probably want to think about the “extended capacity” models, which are able to provide more heating. According to Tim, they don’t cost significantly more and offer more BTUs per hour output. Read more on how to use heat pumps in cold climates here.
Ductless vs. Ducted
If you have existing ductwork in a space, you may consider a different approach when transitioning to heat pumps. Not all heat pumps are ductless. You can get central heat pumps that work with a typical central AC system, and provide heating that blows that hot air through ducts. These central heat pumps are not much more expensive than central air conditioning, and many people think that swapping out every central AC system for a ducted heat pump is an important strategy to quickly get us off natural gas and reduce carbon emissions.
Ductless, on the other hand, is a no-brainer when you’re adding heating or cooling to a room without any ductwork. And DHPs also offer greater efficiency as well as economic and environmental advantages over a central ducted heating system. In addition to the efficiencies mentioned above, ductless heat pumps use inverter technology, which means they run at variable speeds. Tim from the Heat Pump Store compares this to starting your car at a red light. Inverters slowly rev the engine when starting and stopping, while typical central AC systems gun it and brake hard, meaning they are much less efficient. All DHPs use inverter technology, while virtually all conventional (ducted) heat pumps don’t, meaning DHPs are much more efficient.
My family chose ductless heat pumps in our house, rather than a whole house heat pump, even though we had existing ductwork from our old gas furnace because of the increased efficiency.
Humidity and air quality
Though ductless heat pumps help to dehumidify a room, it is not their primary purpose. In places with humidity problems, a separate dehumidifier may still be necessary. Similarly, DHPs have built in air filters, but can’t generally filter air to the extent that ducted systems do with high rated MERV filters. Tim from The Heat Pump Store said that air filtering is considered a separate system, from heating/cooling, in places where heat pumps are most prevalent, and people typically buy another device for air filtration.
There are four leading brands of ductless heat pumps: Mitsubishi, Fujitsu, LG, and Daikin. Most of the top brands are Japanese, given they first developed the technology. This NY Times article has some solid reviews on each of these four brands.
Choosing a contractor
Finding a good installer is important. Many contractors may try to talk you out of electric heating and cooling (and into gas). Plus, you’ll want someone to help you correctly size a system for your needs. That means someone with lots of experience in ductless heat pump systems as well as a good reputation and reviews. Getting three bids is always a solid strategy. One pro tip is to look on a manufacturer’s page for contractors in your area that are certified to install their product.
Cost and Aesthetics
As Tim told me in our interview, ductless heat pumps aren’t a panacea. Any technology has its downsides. As my wife points out, the indoor equipment that sits high on your wall takes up space and isn’t the most beautiful thing in the world. Ductless Heat Pumps can also be expensive. A system with a single indoor unit can run $3,000–$5,000, but if you’re putting multiple “heads” throughout your house, costs can quickly go over $10,000.
Yet, for me, after 9 years of heating and cooling our house with ductless heat pumps, and with the climate emergency we find ourselves in, any drawbacks to ductless heat pumps are vastly outweighed by their immense benefits. Heat pumps are the heating and cooling technology for this era of climate change, and ductless heat pumps are the most efficient versions of this technology. They allow us to get off fossil fuels and efficiently heat and cool, in any climate, with clean electricity.
Learn more and do a deep dive into Ductless Heat Pumps with Tim from the Heat Pump Store in a recent webinar I hosted with Electrify Now, and let us know about your thoughts and experiences with ductless heat pumps in the comments below!
Photo courtesy of The Heat Pump Store