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How Heat Pumps Work: Air-Source Heat Pumps

This week, we are going in-depth in our explanation of how Air-Source Heat Pumps Work. Last week, we discussed Ductless Mini-Split Heat Pumps, but we really didn’t explain how heat pumps work in general. By the end of reading this blog, you will know how your refrigerator, air conditioner, and air-source heat pump work.


The term “heat pump” is fairly misleading, since heat pumps work for both heating and cooling. Air-source heat pumps can be used for radiant floor systems, hot water, radiators, and warm and cool air in your home. If you are replacing an inefficient heating system, like electric heating, you can potentially save up to 75% on your heating and cooling bills!

Besides saving you on operating costs, heat pumps also tend to take up less space and provide better humidification levels than your standard furnace or air conditioner. You can heat your water as well as your air and don’t have to rely on fuel deliveries. Contrary to common belief, heat pumps are all-in-one systems, able to both heat and cool your home and substitute your individual heating and cooling systems.

Air-Source Heat Pumps:

In order to explain how air-source heat pumps work, we will use a refrigerator as an example. Your air conditioner and refrigerator are classic examples of how air-source heat pumps work

Air-source heat pumps take air from low temperature and transfer it to a higher temperature environment. With a refrigerator, the inside has a low-temperature environment and continues to suck out heat from the inside and transfer it to the outside. Air-source heat pumps can continue to suck out heat from an environment even if the temperature is as low as -15 degrees Celsius (Energy Savings Trust).

The Compressor:

A gas is passed through a tube, which is connected to a pump, attached to a motor. The motorized pump forces the gas through larger or smaller spaces to expand or contract the gas. Upon compression and increased pressure, the gas heats up. This is why the coil on the back of refrigerators is hot. The molecules get pushed close together, creating heat.

You have probably noticed this same effect when pumping up your car or bicycle tire: the pump gets hot. When you are using the pump, you are pushing molecules closer together, creating more and more heat.

The Evaporator

Reversing this process creates the opposite effect. When you decrease the pressure of the air, it gets cooler. This is noticeable if you have ever felt the temperature of a spray can of any sort, like Dust-Off, spray paint, or air fresheners. When you press down, you are taking compressed air and releasing it into a low-pressure area, thus creating a cooling effect. as the molecules spread further apart, it cools and evaporates. Letting air out of your car or bike tire produces the same effect.

This is the same cooling effect that your refrigerator uses to produce a cool environment inside your fridge and freezer.

A compressor (like a bicycle pump) will produce heat. An evaporator (like a can of pressurized air) will produce cold. The evaporator turns a liquid into a gas.

Inner and Outer Coils:

If you flip your refrigerator around, you will see a row of coils. Behind the outer set of coils, there is another, cooler set of coils. The inner set of coils get very cold and heat is taken away from the food. The outside coils are hot, allowing the heat to escape to the air outside. The inner tubes are insulated to protect against any heat transfer from the outer coils.

So basically you have gas that is being passed through tubes or coils at different areas in a circuit. When the gas is pressurized (compressor), the gas heats up, which gives off hot air to the surrounding area. This is why the back of your refrigerator is hot. To get the gas cold again, it must be passed through an area of low pressure, which lowers its temperature since the molecules are further apart.

Although many heat pump systems use the more expensive electric resistance heater for backup heat in case of extremely low temperatures, heat pumps can be outfitted with fuel-based backup burners.

Here is a diagram to show you how this heat pump cycle works:

How Does a Heat Pump Work?

Source: shutterstock

The way a refrigerator works is essentially how an air-source heat pump works, but the air-source heat pump can also reverse the process, taking heat from the cold outdoor environment and transferring it indoors. Remember, it can be as cold as -15 degrees C out and your heat pumps will still be able to extract heat from it.

In the summer, the heat pump sucks the heat out of your house and releases it outside. The hot coils on your outdoor unit get its heat from what it gathered inside your home. In the winter, heat is extracted from the outdoor air and transported indoors.

Benefits of an Air-Source Heat Pump

Source: Energy Savings Trust

Watch this video for some more technical stuff:

Located in Champaign, IL, Cassel Home Comfort is your go-to source for all of your heating and cooling needs, including air-source heat pumps.

If you need help deciding if an air-source heat pump is right for you, call your home comfort experts at (217) 866-1596 for your free Whole Home Inspection and Analysis. We are available 24 hours a day, 7 days a week to answer any questions you may have.

We also offer an ongoing Home Maintenance Plan to help ensure your heating and cooling system is at its highest efficiency levels and lasts a long time.

Cassel Home Comfort Heating & Cooling is committed to being your best HVAC contractor choice in Central Illinois in both Value and Customer Service!