Clean Heating and Cooling  |  Air Source Heat Pumps

What are air source heat pumps?

Last updated 5/17/2022

Air source heat pumps are an efficient electric heating and cooling option for your home or business.

air source heat pump system diagram

Most heating technologies, such as a natural gas furnace or electric baseboard heating, work in the same basic way: they modify the temperature of a building by generating hot air circulated throughout the home.

An air source heat pump works differently. Instead of generating heat, it simply transfers heat from one place to another. As a result, air source heat pumps use energy much more efficiently than other technologies and can help with both heating and cooling. In many cases, they offer a smart home energy system upgrade that’s cost and energy efficient.


What's included in this overview on air source heat pumps
  • Components include indoor and outdoor equipment as well as supplemental equipment for managing and monitoring energy usage.
  • There are different types of air source heat pumps, including ducted and ductless. Heat pumps may also be split into zones, depending on your building, needs, and preferences.
  • We break down how an air source heat pump works both for heating and cooling your home.
  • You may want to replace your current HVAC system with an air source heat pump for increased efficiency, reduced reliance on fossil fuels, and cost savings.

Components of air source heat pumps

There are two main components to an air source heat pump system:


Outdoor unit

This may also be called the heat exchanger, containing a coil and fan. The fan blows outside air over the coil, and then the coil operates as a condenser when cooling or an evaporator when heating.


Indoor equipment

The main indoor equipment often called the air handler, also has a coil and fan. The coil acts either as an evaporator for cooling or a condenser for heating. The fan in the indoor unit moves air across the coil and through the ducts. Depending on your heat pump design, you may have multiple air handlers inside, or mini splits if you aren’t using ducts.

Additional components of an air source heat pump system for your home include:

  • Refrigerant: the substance that actually flows through the air source heat pump system via piping, absorbing and rejecting heat as it circulates.
  • Compressor: pressurizes the refrigerant and moves it through the system.
  • Expansion valve: this component inside your home regulates the flow of the refrigerant as it passes through the system, allowing for a reduction of pressure and temperature of the refrigerant.
  • Reversing valve: this part reverses the flow of refrigerant, allowing the system to operate in the opposite direction and switch between heating and cooling.
  • Supplemental equipment: while not part of your actual air source heat pump, you also usually use additional items such as a smart thermostat. Some brands of heat pumps connect only to specific brands of thermostats, so you’ll want to know that before you purchase one.

The specific equipment needed may vary slightly depending on your home’s layout and existing setup as well as the details of the system designed by your contractor.


Types of air source heat pumps

Once your outdoor unit captures heat, it must be distributed throughout your home. Homeowners have various options for distributing the warm or cold air from an air source heat pump including ducted, ductless, and short-run ducted heating and cooling.


Ducted air source heat pumps

Buildings with a ducted heating and cooling system distribute air through a single central path, usually tubes in the walls made from sheet metal.

ducted heating and cooling system diagramWhen ducted might be a fit: If your building already has ducts installed, most contractors will tell you to take advantage of that existing infrastructure and install a ducted system. A major benefit of ducted heating and cooling setups is that they are installed behind walls and in crawl spaces. As a result, you don’t need to worry about the indoor units that need to be installed with a ductless system.


When ducted might not be a fit: Ducts can be expensive and complicated to install, so ducted systems are usually best for new construction or properties that already have ductwork.


Ductless air source heat pumps (also known as mini splits)

ductless heating and cooling system diagramIn a ductless heating and cooling system, warm or cold air is pumped directly to several individual indoor units, which can each be controlled separately. There is no central indoor unit in a ductless system, making it easy to heat and cool different parts or rooms of a building to your preference. Ductless systems are often also referred to as “mini-splits.”

When ductless might be a fit: Ductless systems have many advantages. They are much simpler to install, more efficient than ducted systems, and allow for fine control of the temperature of individual rooms in any building. If you are building a new property or an addition, or are retrofitting a home without a ducted system, a ductless air source heat pump system is a simple and efficient option.

When ductless might not be a fit: If you already have existing ductwork you can use, that might be your most cost effective route to installing air source heat pumps. Some people do see a downside to the aesthestics of mini splits or wall units and would rather not have those visible throughout their home.


Short-run ducted air source heat pumps

If ductwork only runs through a small section of the house or your home has gone through a renovation, you may have a situation where you have short-run ducted heat pumps that you combine with other ductless units for the rest of the house.


Multi-zone air source heat pumps

Depending on the design and installation plan for your air source heat pumps, you may have two or more indoor coils connected to one outdoor condenser. Multi-zone indoor coils vary by size and style and each creates its own "zone" of comfort, allowing you to heat or cool individual rooms, hallways, and open spaces. This distinction may also be referred to as "multi-head vs. single-head" and "multi-port vs. single-port."


How does an air source heat pump work?

At its simplest, an air source heat pump is both a heating and cooling system that moves heat inside during the winter and outside during the summer. This HVAC option is a cost and energy-efficient method for heating and cooling your home.


Heating your home with heat pumps

1. Outside air is drawn into the unit

This step begins at the outdoor unit of the heat pump. Outside air is drawn in with the use of a fan.

2. Heat from the outside air transfers into the system.

The air flows over a tube with refrigerant fluid being pumped through it (known as a heat exchanger). The refrigerant is colder than the outside air, and as the air flows over it, heat is transferred to it, which warms the liquid.

3. The heat is concentrated in the system’s heat exchanger.

As the liquid refrigerant is warmed through the heat exchanger, it turns to vapor in the same way that boiling water turns to steam. The vapor is then compressed to concentrate the absorbed heat.

4. The heat is moved into your home.

The concentrated hot vapor passes through a second heat exchanger, which supplies the heat energy to your house. 

As your home warms up, the vapor cools and is pumped back through the first heat exchanger to collect more heat energy from the outside air. This happens continually to maintain your air temperature.


Cooling your home with heat pumps

In warmer months, this process simply runs in the opposite direction to cool your home. Instead of transferring the heat from outside air to inside, the refrigerant is pumped through a heat exchanger inside your home first, where it absorbs heat energy and moves it outside.


Replacing your current HVAC system with an air source heat pump

If your current HVAC system is nearing the end of its life, when looking to repair or replace existing heating and cooling systems, an air source heat pump may be an efficient solution for your home. You’ll need to weigh certain factors such as the cost to install heat pumps based on your home’s layout, structure, and existing ductwork. While initial upfront costs usually are higher than other , you can often save money long-term when factoring in decreased utility bills, rebates and incentives, and increased efficiency.


Finding a trusted air source heat pump contractor

Just like any home upgrade or project, you want to find a trusted contractor in your area to help quote, guide you through the process, and install your heat pump. You can speak with your neighbors or colleagues, read local reviews, and speak with local contractors to get answers to your questions. They can help you assess the validity of going with an air source heat pump as well as design your system to meet your needs.

Air source heat pumps are commonly used to regulate the air temperature of a building, which is known as an “air to air” systems. However, you can also use an air source heat pump as part of an “air to water” system, in which heat generated from the outside air can be sent to radiators, underfloor heating, and hot water systems.

FAQ: Is buying air source heat pumps worth the upfront investment?

Air source heat pumps typically cost more than traditional heating and cooling systems; however, a well-installed air source heat pump system is capable of providing 1.5 to 3 times the amount of electrical energy it consumes in the form of heat energy for your home. Lower electricity requirements mean lower energy bills over time.

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