Size (Capacity)
A heat pump that’s too small for your needs will struggle to keep your home comfortable. On the other hand, an oversized unit will cost more, and if it isn’t a variable-speed model, it will cycle on and off more often than it should. This decreases efficiency, stresses components, and leaves your home less comfortable.
A heat pump’s cooling capacity is measured in British thermal units per hour (Btu/hr.). Btu/hr. can also be expressed in “tons,” with 1 ton equaling 12,000 Btu/hr. To ensure that your heat pump is sized correctly, make sure your contractor does a load calculation based on a recognized method, such as the Air Conditioning Contractors of America (ACCA) Manual J. The calculations should be done after any air-sealing or insulation upgrades are made to your home and should be done whether you’re replacing a unit or installing a new system.
One nuance to consider: If you’re planning to keep a backup heating system alongside your heat pump, consider getting an undersized heat pump. A contractor can help you figure out whether this makes sense in your home.
Note that heat pumps need far less capacity to heat a space than a furnace or boiler would because they’re much more energy-efficient. For example, if your home needed a 100,000-Btu/hr. furnace, it may need only a 36,000-Btu/hr. heat pump.
Compressor Type
The compressor is the heart of a heat pump—it’s the part that actually pumps the heat. Basic heat pumps have a single-speed compressor. It’s either on or off. This system works well enough, but the temperature and relative humidity in your home will swing up and down with the cycles. Some compressors have two speeds, which mitigates the swings, but they’re still present.
The gold standard is a variable-speed compressor. It’s designed to run almost constantly, adjusting itself over time to deliver only as much heating or cooling as it takes to keep your home comfortable. It’s also much better at keeping relative humidity under control than single-speed models are.
Variable-speed compressors not only keep your home more comfortable but also are more energy-efficient. It may seem counterintuitive, but it takes much less energy to move a tiny bit of heat all the time than to move a lot of heat quickly.
Efficiency
Some heat pumps use less energy than others to deliver the same level of comfort. In cooling mode, efficiency is commonly expressed as the seasonal energy-efficiency rating, or SEER. The higher the SEER, the greater the efficiency. In heating mode, the measurement used is the heating seasonal performance factor, or HSPF. Again, the higher the number, the more energy-efficient the unit.
As of January 2023, the Department of Energy adopted new testing methods for energy efficiency, replacing the SEER and HSPF values with SEER2 and HSPF2, while also increasing efficiency standards.
Heat pumps with higher SEER/SEER2 and HSPF/HSPF2 ratings tend to cost more, but they’ll often pay for themselves over time through lower energy costs, and they may be eligible for better tax incentives or rebates than less efficient models. Heat pumps with higher SEER ratings also tend to have higher HSPF ratings, though there’s no direct relationship between the two. If you live in a warm climate, pay closer attention to the SEER. In cold climates, look for a higher HSPF.
Climate Performance
If you live in a region with cold winters, you’ll need to either pick a heat pump that’s rated to work well in the lowest temperatures that your region regularly experiences or have a secondary heating system to back up your heat pump.
All air-source heat pumps struggle to perform as temperatures drop; the space they can effectively heat shrinks and they don’t work as efficiently. The threshold for poor performance varies from model to model. Some heat pumps falter at 25° F, others at 17° F or lower.
Models marketed as cold-climate heat pumps can work to their full potential all the way down to 5° F and may deliver some heat even down to -20° F or lower. The best course is to work with a qualified local contractor who knows what kind of equipment works well in your area.
If you live in an area where the temperature rarely or never drops below freezing (32° F), a basic heat pump can handle the bulk of your heating and cooling needs. You can keep a simple electrical-resistance backup system (sometimes built into the heat pump itself) for unusual cold snaps.
Noise
Manufacturers publish the noise levels of their products in the user manual and often on their websites. They tend to include noise estimates across a variety of outdoor temperatures and fan speeds, measured in decibels. A lower rating is better, especially if the heat pump will be installed near a bedroom window.
Reliability
In our member survey, heat pumps from eight brands were judged highly reliable, but only two of them also got top marks for owner satisfaction. Consumer Reports members can see the predicted reliability and owner satisfaction ratings for 29 brands of heat pumps, based on data that CR members have shared about 10,158 heat pumps they bought new and installed in their own homes between 2007 and 2023. Those findings are summarized in our guide to the Most and Least Reliable Heat Pumps.
Heat pumps can be split into three main types: air source, ground source (geothermal), and water source. The type you choose will depend on factors such as the heat source(s) and installation space available, the existing heating systems, and your budget.
Air source heat pumps extract heat from outdoor ambient air and transfer it indoors. They can be air-to-air or air-to-water.
Air/air heat pumps transfer the heat to interior air handling units, which blow the air directly into one room, or into different spaces via a ducted system. They can be used in reverse as air conditioners. They are an economical and easy-to-install choice for small homes, apartments, and commercial spaces but cannot be used for hot water heating.
Air/water heat pumps transfer the heat from the air to a wet central heating system such as hot water radiators or underfloor heating. Some models can also be used to heat domestic hot water. Although air-to-water heat pumps tend to be more expensive than air-to-air, they are a popular choice for buildings with existing central heating systems because they can be easily installed and do not require ducting or air-handling units. Be sure to choose a heat pump that is compatible with the existing heating installation. For example, check whether it is a high-temperature or low-temperature system.
Geothermal heat pumps use a heat transfer fluid such as antifreeze and buried pipes to extract heat from the ground. The heat transfer fluid is then compressed through the heat exchanger to transfer the heat to the heat pump. They tend to be very efficient because the ground temperature stays more stable than the air temperature throughout the year. However, installation can be costly and the depth and surface area of the ground required for it will depend on the heating and cooling needs of your space. It is best to get professionals to calculate this. For ground/water systems, the heat is transferred from the heat pump to the heating system and/or domestic hot water system.
Water source heat pumps work in a similar way to geothermal systems, except the pipes are submerged in a body of water such as a lake, river, or pond. If the water is close to your property, this might be easier to install than a buried geothermal system. For water/water systems the heat pump transfers the heat to the central heating system and/or domestic hot water system. Water source heat pumps tend to be more efficient than air source heat pumps because heat transfers better through water and large bodies of water tend to hold a more stable temperature throughout the year.