Heat pumps are remarkable inventions. Rather than actually creating heat through combustion or resistance, a heat pump removes heat from the air, water, or earth and transfers it elsewhere through a refrigerant. Because of how they operate, heat pumps can both heat and cool your home. In warm weather a heat pump works to pull heat out of the warm air inside your home and transfers it outside. In cold weather, it does the opposite.
Standard heat pumps are big mechanical units that sit outside your home, and they look much like an air conditioner compressor. They can work for both central heating and cooling, and they work best in milder climates but not as well in extremely cold climates.
Heat pumps do have an ideal operating range. The latest units can operate effectively in temperatures down to 0°F, according to Trane, one of the large manufacturers. Obviously that’s not going to be sufficient in January in Minnesota, where temperatures can stay at -10°F for a couple of weeks at a time, so you'll want to consider supplemental heating such as a dual-fuel system if you live in a frigid climate. (though Maine has extremely high adoption rates)
Heat pumps come in a few different varieties: air source, ground source, water source, and dual source. A mini-split will be an air source heat pump and we’ll get back to those. Ground source heat pumps use loops of plastic piping laid into the earth. Water source heat pumps place the loops into a body of water. Dual source heat pumps combine two of those options. The heat pump circulates a refrigerant through the tubing that can either absorb or release heating or cooling energy, then it’s pumped back into the house where the heating or cooling energy is transferred to water or air so it can be used for home heating, cooling, and/or domestic hot water.
Heat pumps typically use ductwork to distribute conditioned air, making them a common alternative to a gas furnace and central air conditioning. They can be part of a radiant system that circulates hot water as well. They’re more efficient than a gas furnace/central AC combo, but that efficiency drops off as the ambient temperature falls.
Ground-source heat pumps, however, do not lose efficiency in cold weather the way that air-source heat pumps do. That’s because the earth remains at a more constant temperature year-round than the air, so there’s more heat energy to extract and move into the house.
Ground-source heat pumps require a lot more work to install, though, as the collector loop requires quite a bit of land and excavation work to install. Homeowners can usually recoup that cost over time with lower energy costs compared to burning fossil fuels. Once installed, though, ground source heat pumps tend to be low maintenance and have a service life of about 15 years, give or take.
If your home already has ductwork, a standard ducted heat pump may be more attractive to you than a mini-split system. Ducted heat pumps can be set up to use existing ductwork just like typical furnaces and central air conditioners. That ductwork is less visually obtrusive than a mini-split system and tends to work just fine, even if that type of system is a bit less customizable room by room. Mini-splits do have the advantage of dialing in the temperature of each room they’re located in, and you’ll use a remote control to operate it.
Mini-splits are a form of heat pump with a different way of delivering conditioned air to a room. Instead of pushing warm or cool air through metal ductwork, a mini-split uses an outdoor compressor/condenser unit with one or more indoor air handlers/evaporators. The compressor is connected to the air handler(s) with electrical lines and a refrigerant line, requiring only a small hole through the wall.
A big advantage of mini-split systems is their flexibility. Since there’s no need for ductwork, mini-split systems are ideal for retrofitting in homes without existing ductwork. As we’re seeing climate change deliver record temperatures all over the world, more homes actually need air conditioning for safety as well as comfort.
Also, mini-splits will dehumidify warm air as part of the cooling process, which is crucial in much of the U.S. Pioneer, a mini-split maker, says their units will lower humidity by 44–55% and the ideal humidity at home is between 30–40%. If you live in a place with a humid climate, it’s possible that you would want a dehumidifier in addition to a mini-split system.
Also, like other heat pumps, mini-splits are extremely efficient and cost less to run than other HVAC systems. A part of that efficiency is due to the multi-zone nature of mini-split systems. Some systems let you use up to four air handlers per compressor, so you can control the heating and cooling in each zone or room individually, unlike the typical whole-house approach of other HVAC systems.
Drawbacks to mini-split systems include the appearance of the air handlers. This is subjective, of course, and may not bother you at all. The air handlers are available as wall mounted, ceiling mounted, and floor standing units, so you do have some flexibility with that.
You’ll find a big range in pricing, but according to HomeAdvisor, you’re looking at $4,500 to $8,000 for a ducted system. For a mini-split system, the range is $1,300 to $8,000 but it really depends on how many air handlers you need and how far they are from the compressor.