Air Source Heat Pumps

An air source heat pump (ASHP) is a mechanical system that uses electricity to both heat and cool your home. In warm months, it pulls warm air out of your home to make it cooler, and in cool months, it pulls heat from outside (even small amounts) into your home to warm it. The pumps can either connect to your existing ductwork, or if you don’t have air ducts in your home, they can be mounted separately in individual rooms (called “ductless” or “mini-split” air source heat pumps). Because the heat pumps are moving air, rather than heating or cooling the air, they are highly efficient.

Depending on your existing heating and cooling systems, ASHPs can help residents save money and reduce household greenhouse gas emissions. An ASHP may also be an option for parts of the home that may be challenging to heat or cool with your existing system.

An air source heat pump differs from a ground source heat pump. Ground source heat pumps, also called geothermal systems, pull heat from the ground rather than the air, and the installation process differs from ASHPs. Find out more about ground source and geothermal heat pumps from the Minnesota Department of Energy here.

ASHPs are great options for households already using electric resistance, propane heating, or fuel oil systems that are looking to save money on their heating costs. They are also an option for consumers who want to reduce their use of fossil fuels (natural gas, propane, or heating oil) and move towards an electric heating system.

Many homes in Minnesota have natural gas-powered furnaces and boilers. Because the historic cost of natural gas tends to be lower than using electric resistance heaters and the cost of propane, air source heat pumps typically do not provide cost savings for homes heated with natural gas. If the cost of natural gas were to increase, and depending on the cost of electricity, ASHPs may become more affordable than natural gas-only heating systems.

If you are concerned about greenhouse gas emissions and want to reduce your household’s reliance on fossil fuel-based heat sources (such as natural gas, propane, or fuel oil), air source heat pumps can be a great option. Because they run on electricity and our electric grid is powered by increasing levels of renewable energy, converting from fossil fuel heat to electric heat lowers your carbon impact.

ASHP technology is rapidly improving, and heat pumps called “Cold Climate air source heat pumps (ccASHPs)” can heat homes when air temperatures are as low as approximately -13 ºF.

However, most homes in Minnesota should still have a backup heating system. Some ASHP users opt for an electric backup alongside their ASHP, while others use natural gas, propane furnace, or other fuel.

The Minnesota Air Source Heat Pump Collaborative’s Cost of Heat Comparison Tool shows the cost savings associated with conventional vs. electric backups, and shows how costs vary depending on the “Switchover” temperature. This is the temperature at which you switch from using the ASHP to heat your home to using the backup heating system.

If you have a propane heating system, an ASHP tends to be more affordable in lower temperatures. If you have natural gas, ASHP heat likely will cost you more money to operate during the cold weather months. Typically, ASHPs can be most affordable to operate during shoulder seasons when temperatures remain above 40 to 45ºF. For example, using a switchover temperature of 35ºF throughout the winter would likely cost you slightly more than using a gas furnace. Natural gas furnaces tend to be more affordable given historical gas prices. As gas and electricity prices fluctuate, the comparative operational cost of an ASHP can also rise and fall. The Air Source Heat Pump Collaborative has a contractor tool that can help estimate these costs.

If you currently use a fossil fuel (natural gas, propane, or heating oil) as your primary heat source, ASHPs can help you reduce your greenhouse gas emissions because they run on electricity. Most utilities in Minnesota use a combination of renewable and non-renewable energy sources, so your electricity can have a lower carbon footprint than a fossil fuel-based heating source. The exact emissions reductions depend on your current heating source as well as the energy sources that your electric utility uses.

In addition, if you use electric resistance heat, ASHPs are more efficient and can help reduce your household’s total energy use.

An ASHP is typically permanently installed in a building, and so would require landlord approval (though window-mounted air source heat pump units may be hitting the market soon). Depending on your home’s current heating source, an ASHP could help reduce heating costs for current and future tenants.

The upfront cost for ASHPs can be in the thousands of dollars. The exact cost varies depending on several factors, including the size of your home, its current heating and cooling systems, and the type of ASHP you install. It often costs a bit more to install an air source heat pump rather than a conventional air conditioner.

Most utilities offer rebates for ASHPs, and the Minnesota air source heat pump Collaborative has a map to help you find rebates in your area.

If you qualify for income-based energy assistance and the federal weatherization program, an ASHP could be installed at no cost to you (or to your landlord, if you rent your home). Your eligibility varies depending on your primary heating source and may only be available to households heated by electricity.

It depends on your priorities. As discussed above, even though they may cost more up front, air source heat pumps can save money overall for homes that heat with electricity, propane, or fuel oil. In Minnesota, ASHPs tend to create more savings in heating costs rather than cooling costs, and replacing an air conditioner with an ASHP may not reduce your cooling costs.

ASHPs can be quieter than window A/C units and also effectively dehumidify air. If you are already thinking about installing ASHPs for heating, they also have benefits for cooling.

ASHPs have temperature settings just like existing heating and cooling systems. With the press of a button, either via a remote control or on the indoor heat pump unit itself, you can change the temperature, fan, and humidity settings.

One key difference between air source heat pumps and conventional heating and cooling systems is that ASHPs usually work best with the “set it and forget it” approach during the winter. You might be used to adjusting your thermostat during the day or in the evening, but because ASHPs are most efficient when maintaining a continuous temperature, it’s best to keep them at a consistent setting and not adjust it throughout the day and night, especially during the winter.

Efficiency Maine provides more user-friendly tips about temperature and fan settings for ASHPs here.

In cold climates like Minnesota, you will need to decide when to switch from heating with an ASHP to using your backup heating system. As previously mentioned, ASHPs in Minnesota tend to be cost-effective when switching to backup heating around 40º or 45º F. This switchover temperature varies depending on the type of heat pump you have and your backup heating source, so check with your installer and user manual for recommendations. Try testing out different switchover temperatures to see which you prefer in terms of energy and cost savings.

Because ASHPs have an outdoor pump component, be sure to keep this exterior unit clear of snow, leaves, and debris to ensure maximum efficiency (just as you would a central A/C unit). Clean the interior units regularly (every few months or so) to prevent dust buildup.

If you’re not ready to install an ASHP, think about the lifetime of your current heating and cooling systems. Most furnaces and central air conditioners need to be replaced every 15 to 20 years. Start to plan for how you’d like to replace your system when it reaches the end of its life and if an ASHP can be part of that system.

In addition, make home energy efficiency improvements by weatherizing your home, upgrading other appliances as needed, and even getting a home energy audit. ASHPs work best in well-insulated homes that are already efficient.

Start by making sure that your home is well-weatherized. ASHPs work best in homes that are already efficient.

Once you’re ready to install, look for qualified contractors. Ask questions about their experiences with ASHPs, because not all HVAC companies have previously installed ASHP systems. The Minnesota Air Source Heat Pump Collaborative and this article from the New York Times. provide suggestions about what to look for in an ASHP contractor.

Make sure the contractor discusses sizing the ASHP correctly. Heat pumps that are too large or too small for your home will not work as efficiently.