Ductless Heat Pumps Demystified | CleanTechnica

Climate change has the strange effect that many of us are overly excited about devices that were never important to us before. Suddenly, all the background machines that previously unconsciously drive our lives have acquired an over-dimensional importance. Some of them have the potential to provide the essential services we depend on while not destroying our planet, like the fossil fuel machines of the 19th and 20th centuries.

Ductless heat pumps are a prime example of this. In the past, many of us have used gas stoves and boilers to heat our homes and burned fuels, releasing large amounts of CO2 in the process. With the magic heat pump, we now have access to efficient electrical technologies for heating and cooling that can be operated entirely with renewable energies and are therefore climate-neutral.

Photo courtesy of The Heat Pump Store

Brief history and growth of ductless heat pumps

Ductless heat pumps (DHPs) were developed in Japan after World War II. Invented and perfected on an island that has no easy access to fossil fuels, they are the ideal heating / cooling system for our modern world. do not rely on combustion and are also incredibly efficient.

They condition 90% of Japanese homes and their usage is growing like crazy worldwide, with heat pump sales expected to double over the next five years. UK sales are projected to grow 20x and US sales are forecast to grow in some areas north of 40% every year.

My family has been using ductless heat pumps for heating and cooling since purchasing our home in 2012. The gas stove that came with our house was old and we decided to replace it with new ductless heat pumps. (A big benefit is that wall mounting saved valuable floor space in the garage that was previously dedicated to the gas stove that we converted into an apartment). We had seen them in Europe and already thought 9 years ago, when the electrification movement was still in its infancy, that heating with efficient electricity would allow us to reduce our CO2 emissions with the solar panels we wanted to install on our roof .

Photo by Joe Wachunas

What is channelless?

But what is a ductless heat pump (also known as a mini-split)? Basically, it is a heating / cooling system that differs from a conventional oven in several ways:

1. DHPs have no air ducts. Instead of forcing hot air through potentially leaky ducts, ductless systems place an indoor unit on a wall and an outdoor unit (similar to a typical AC unit) that provides heating and cooling. This prevents air from escaping through leaky channels, which leads to more efficient conditioning.

Indoor unit. Photo courtesy of The Heat Pump Store.

2. DHPs don’t burn things. Ductless heat pumps use electricity for heating and cooling. Electricity is rapidly evolving towards fully renewable and will therefore soon be emission-free (for example, the Biden government set the 2035 target).

3. DHPs are like inverted refrigerators. Instead of burning fuel, ductless heat pumps generate heat and cold through cold. That means they take the heat from the outside (even if it’s cold) and transport it into your house and vice versa for cooling. It’s pretty magical. The refrigerants used by DHPs can themselves be powerful greenhouse gases, but luckily the world is rapidly moving towards better, greener refrigerants (see This website for a new type of refrigerant called R32).

Refrigerant lines of ductless heat pumps. Photo courtesy of The Heat Pump Store.

4. DHPs are incredibly efficient. This is because a) no air escapes through the ducts, b) they heat the room they are in (and not the whole house), c) the movement of heat is much more efficient than generating it, and d ) they use inverter systems (see below). As a result, they usually use three times less energy than old electrical resistance heaters and six times less than gas.

Demystifying some DHP terms

Speaking of efficiency, let’s demystify a few terms associated with ductless heat pumps.

SEHER – SEER is a number that measures how well a technology provides cooling. The higher the number, the more efficient the device is. Most new air conditioners have a SEER between 13 and 21, but Ductless can often see a SEER above 30, which gives you an idea of ​​how efficient they are. When you are in a warm climate, SEER is especially important.

HSPF – HSPF stands for Heating Season Performance Factor and complements the SEER assessment, as it measures how efficiently a heat pump heats a room. The minimum required HSPF rating in the US is 7.7. A score of 8.5 is considered good and over 10 is considered excellent. If you find yourself in a cooler climate where the majority of energy consumption is for heating, HSPF is most important.

Example of SEER and HSPF scores

I interviewed Tim Sharp, out the heat pump store here in Oregon that has installed thousands of ductless heat pumps in the past decade. He said that you want your DHP to be most efficient at heating when you are in a cold climate and cooling when you are in a warm climate. People in the northern US should likely focus on HSPF, while people in the southern US should focus on SEER. Tim also said that investing in a DHP with higher values ​​upfront is more expensive, but the additional costs usually amortize over time through energy savings.

Ductless heat pumps in cold weather

I also learned from Tim that DHPs were originally only developed for cooling (like a refrigerator), but that they “have just gotten better and better in almost every heating environment”. If you are in a cold climate, you will likely want to go to the “expanded capacity“Models that can deliver more heat. According to Tim, they don’t cost much more and offer more BTUs per hour of performance. Read more about the use of heat pumps in cold climates here.

Channelless vs. Channeled

If a room already has air ducts, consider another approach when transitioning to heat pumps. Not all heat pumps are ductless. You can purchase centralized heat pumps that use a typical central air conditioning 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 replacing every central air conditioning system with a duct heat pump is an important strategy for quickly separating us from natural gas and reducing CO2 emissions.

Ductless, on the other hand, is a breeze if you want to heat or cool a room without ducts. In addition, DHPs offer greater efficiency as well as economic and ecological advantages compared to central duct heating. In addition to the efficiency levels mentioned above, ductless heat pumps use inverter technology, which means that they run at variable speeds. Tim from the heat pump store compares this to starting your car at a red light. Inverters slowly bring the motor up to speed when starting and stopping, while typical central AC systems brake hard and brake hard, which means they are much less efficient. All DHPs use inverter technology while practically all conventional (duct) heat pumps don’t, which means DHPs are much more efficient.

My family decided to use ductless heat pumps instead of a whole house heat pump in our house, even though we had existing pipes due to the higher efficiency of our old gas stove.

Photo courtesy of The Heat Pump Store

Humidity and air quality

Although ductless heat pumps help dehumidify a room, this is not their main purpose. A separate dehumidifier may still be required in locations with moisture problems. Similarly, DHPs have built-in air filters, but generally cannot filter the air to the same extent as can duct systems with highly rated MERV filters. Tim of The Heat Pump Store said that in places where heat pumps are most common, air filtration is seen as a separate system from heating / cooling and people usually buy another device to filter the air.


There are four leading brands of ductless heat pumps: Mitsubishi, Fujitsu, LG and Daikin. Most of the top brands are Japanese since they developed the technology first. this NY Times article has some solid reviews on each of these four brands.

Selection of a contractor

Finding a good installer is important. Many contractors may try to talk you out of electric heating and cooling (and gas). You also want someone to help you properly size a system for your needs. That means someone with a lot of experience in ductless heat pump systems as well as a good reputation and reviews. Receiving the Three Commandments is always a solid strategy. A pro tip is to check the manufacturer’s site for contractors in your area who are certified to install their product.

Photo courtesy of The Heat Pump Store

Cost and aesthetics

As Tim told me in our interview, ductless heat pumps are not a panacea. Every technology has its downsides. As my wife points out, the interior decoration, which is high on the wall, takes up space and is not the most beautiful thing in the world. Ductless heat pumps can also be expensive. A system with a single indoor unit can cost $ 3,000 to $ 5,000, but if you put multiple “heads” around the house, the cost can quickly rise to over $ 10,000.

But for me, after 9 years of heating and cooling our house with ductless heat pumps and the climate emergency we are in, all the disadvantages of ductless heat pumps are far outweighed by their immense advantages. Heat pumps are the Heating and cooling technology for the age of climate change and ductless heat pumps are the most efficient variants of this technology. They enable us to get rid of fossil fuels and to heat and cool efficiently with clean electricity in any climate.

Learn more and dive into a. With Tim from the Heat Pump Store. deep into ductless heat pumps last webinar I’ve hosted with Electrify now, and let us know your thoughts and experiences with Ductless Heat Pumps in the comments below!

Photo courtesy of The Heat Pump Store

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