Air-to-air heat pumps: what they do and don’t do
An air to air heat pump takes heat from outdoor air and releases it as warm air inside the house, either through ducts or through wall and ceiling units. It also cools in summer, but it does not heat water for radiators, in-floor loops or taps, which is the job of an air-to-water system.
What is an air to air heat pump?
It is the most common type of heat pump in Canadian homes. The outdoor unit collects heat from the air, the refrigerant cycle lifts its temperature, and an indoor unit blows the heat into the room as warm air. Reverse the cycle and the same equipment moves heat out of the house in summer. The refrigerant stays in a sealed loop between the two units, as described in our heat pump explainer.
Most air-source heat pumps sold for homes fall into this group, which is why the air source heat pump guide and this page overlap. The difference is that this page contrasts air delivery with water delivery.
How does air to air differ from air to water?
The names describe the outdoor heat source first and the indoor delivery second. Air to air delivers heated air. Air to water delivers hot water to radiators, fan coils or underfloor heating, and can also charge a hot water tank.
- Air to air: simple, widely available, cools as well as heats, and works with ducts or ductless units.
- Air to water: suits houses that already have hydronic heating, and runs best with low-temperature emitters such as in-floor heating. See low-temperature hydronic heating and the radiant floor heating guide.
Domestic hot water is the main gap in the air-to-air case. The heat pump does not heat it, so the home keeps a separate water heater or adds a heat pump water heater.
What forms does an air-to-air system take?
There are three layouts. A ducted system connects an air handler to the home’s ducts and replaces a furnace, as explained in using existing ducts. A ductless system puts indoor units in rooms, described in ductless heat pumps explained. A multi-zone system links several indoor units to one outdoor unit.
Which layout fits depends on the house. Our guide to mini split versus central ducted compares the two.
Where does an air-to-air heat pump work well?
It works well as a retrofit in homes with ducts or in those without any distribution system, and where cooling is wanted as well as heating. Installation is simpler than air-to-water because no water piping or hydronic changes are needed. It is also efficient, since it delivers heat directly into the air without an extra water step.
It fits less well where the house uses radiators or in-floor loops and you want to keep them, or where hot water demand is a priority. Drake Landing took a hydronic route: district-loop water warmed each house through an air handler (see the air handler page), a reminder that distribution method and heat source can be chosen separately.
What should you check for a Canadian home?
Cold performance comes first. Capacity and efficiency drop as the outdoor temperature falls, so look at low-temperature data and ratings, as explained in cold climate heat pumps. Next is sizing, covered in sizing for cold climate homes. Finally, decide how you will heat on the coldest days: electric elements, a furnace or another backup.
Quick answers
What does air to air heat pump mean?
The heat comes from outdoor air and goes into indoor air. The system heats and cools rooms with warm or cool air, rather than heating water.
Can an air-to-air heat pump heat my hot water?
No. It heats only the air. You would need a separate water heater or a heat pump water heater for hot water.
Is air to air or air to water better?
Neither is better everywhere. Air to air suits homes with ducts or no distribution and a need for cooling, while air to water suits homes with radiators or in-floor heating.
Do air-to-air heat pumps work in cold weather?
Cold climate models work well below freezing, though output falls as it gets colder. Check the low-temperature data and plan for backup heat.