Air Source Heat Pump Buying Guide for Homeowners

Kristi Pahr
Written by Kristi Pahr
Updated December 21, 2021
woman warm and cozy at home drinking tea
Photo: Rido / Adobe Stock

 Keep your home cozy all winter with an air source heat pump

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What is an air source heat pump? Chances are you have a giant mechanical box sitting outside your home that you take for granted. You see it every day, mow around it all summer, and hear it click on and off during both cold and hot weather. You know it’s there and what it’s for, but like most of us, you probably have no idea how in the world it works. 

Air source heat pumps are one of the most common climate control devices, especially in locations with mild winters. If you’ve ever wondered how in the world it works to keep your home comfortable, read on!

What Is an Air Source Heat Pump? 

An air source heat pump is a climate control device used to heat and cool your home. It uses refrigeration principles to provide cool air in the summer and warm air in the winter. The unit transfers heat from one place to another resulting in warmer or cooler indoor air.

How Does an Air Source Heat Pump Work?

Heat pumps work by removing heat from outdoor air and moving it inside. Unlike other heat sources like gas furnaces, heat pumps do not burn fuel to create heat, making them a more cost-effective heating solution for those in places with milder winter climates.

All air, until it reaches absolute zero, the temperature at which things can get no colder, contains heat. Even if it feels cold outside, the heat in the air is what keeps it from being absolute zero, which is equivalent to -273 degrees Celsius. Extracting this heat is what air source heat pumps excel at. 

In the winter, air source heat pumps are effective at extracting heat from outdoor air down to about 5 degrees Fahrenheit. This heat is then concentrated and pushed into your house to keep you warm. 

In the summer, air source heat pumps do the opposite. They remove the heat from indoor air and push it outside, replacing it with cool air to keep your home comfortable even on the hottest days. 

Components of an Air Source Heat Pump System

heat pumps installed outside home
Photo: Nimur / Adobe Stock

Air source heat pumps are made up of two units that work together to heat or cool your home—an outdoor unit and an indoor unit. The outdoor unit contains an evaporator, a compressor, a condenser (or heat exchanger), and an expansion valve. 

The indoor unit houses the fan, indoor coil, and a secondary heating element. The two units are connected by refrigeration tubing.

The components make a loop, and air passes through it in the following way: 

  • Outdoor air enters the system through the evaporator, where heat is absorbed by the refrigerant.

  • The refrigerant transforms from a liquid to a gas and enters the compressor.

  • The compressor reduces the volume and heats the gas.

  • The warmed gas enters the condenser, and the heat is removed and shunted toward the indoor unit, where the fan blows it through your ductwork and into your home.

  • After the heat has been extracted from the gas, it returns to liquid form and travels through the expansion valve, where pressure is released. The depressurized refrigerant then travels back to the evaporator, and the cycle begins again.

Air Source Heat Pump Installation

Installing an air source heat pump is a complex project that involves both electricity and plumbing and should only be undertaken by a qualified HVAC professional. 

Your HVAC tech will follow these steps when installing your air source heat pump:

  • Install the indoor unit and new ductwork or reroute existing ductwork to the new unit.

  • Create an access point for tubing and electrical lines to run between the indoor and outdoor units. The installer will have to drill a hole through your exterior wall to accomplish this.

  • Connect refrigerant and condensation drain lines to the indoor unit.

  • Install the outdoor unit. Your contractor may also pour a concrete slab for the unit to rest on.

  • Connect electricity. Your installer will connect the indoor and outdoor units to each other and to your home’s wiring.

How Much Does an Air Source Heat Pump Cost?

The average cost to install a new air source heat pump is around $6,000. Depending on the size of your unit, the cost can range anywhere from $4,000 to $8,000. These prices do not include the cost of installing new ductwork. The cost to install new ductwork is from $400 to $2,500.

What Size Air Source Heat Pump Do I Need?

Heat pump size requirements are affected by your climate, the size of your home, the age of construction, the amount of insulation, and the layout of the home. Choosing the right size heat pump for your home is important. A too-small unit will run constantly to keep up with demand and result in skyrocketing electricity bills.

The figures below are a ballpark estimate, and you should discuss size with your HVAC contractor to be sure you get the best air source heat pump for your unique home.

The heating and cooling capacity of the heat pump is expressed in tons. One ton is the same as 12,000 Btu/h.

  • 2 ton: 1,000 sq. ft.

  • 3 ton: 1,500 sq. ft.

  • 4 ton: 2,000 sq. ft.

  • 5 ton: 2,500 sq. ft.

  • 6 ton: 3,000 sq. ft.

Air Source Heat Pump Pros and Cons

Air source heat pumps are great, but they may not be for everyone. If you’re trying to decide if an air source heat pump is for you, read on to find out the pros and cons before you take the plunge.


  • Low maintenance

  • Long lifespan

  • Low carbon footprint since it doesn’t burn fuel for heat

  • Can both heat and cool

  • More energy efficient


  • Not as efficient at temperatures below 5 degrees Fahrenheit

  • Large outdoor footprint

  • Can be noisy

  • Higher upfront cost

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