Functioning as an alternative to conventional gas or oil boiler heating systems, air source heat pumps are units installed outside of a home and utilize thermal energy naturally stored within the air to provide heat and hot water.
Air source heat pump systems work differently compared to a traditional heating system, as they typically extract and release heat more slowly.
This means that an outdoor heat pump unit needs to be coupled with the appropriate indoor apparatus to ensure that heat is distributed efficiently and effectively.
A water tank is not typically required with an air source heat pump when used for heating or cooling. However, a water tank will be needed when an air to water heat pump is also being used to provide domestic hot water, as a heat pump can’t provide sufficiently hot water on demand.
Our air source heat pump system uses a hot water tank located inside our home to store hot water for use in taps, showers etc. across our home.
While this tank stores water for when hot water is required, it also contains electric immersion heaters to help top up the water temperatures to optimal hot water temperatures as needed, such as when there are a larger number of people in the house and demand for hot water is higher.
We discuss in more detail below more about why our air source heat pump needs a hot water tank, why a hot water tank may not always be required and in what situations one would be needed.
Do You Need A Water Tank With An Air Source Heat Pump?
An air source heat pump (ASHP) is an electrical appliance that sits outdoors and extracts heat energy within the outside for use in a home; primarily for heating, but can also be used for domestic hot water.
Our ASHP is located down the side of our house and is shown below.
While this heat pump provides us with both heating and hot water, a hot water tank is required in order for us to have hot water.
Air source heat pumps extract and deliver heat more slowly compared to these other conventional heating systems and so need more time to bring water temperatures up to what we would consider ‘hot’.
A water tank allows water to be stored and brought up to desired hot water temperatures.
As a result, a hot water tank is typically required when using an air source heat pump to deliver hot water to a home, such as for taps, showers, baths etc.
The water tank for our air source heat pump is located within a cupboard in our home, along with all the other necessary heating and hot water apparatus.
Water tanks for hot water when using an air source heat pump can be quite large and so you’d need to consider where this tank would be placed in your home. Inside a suitably sized cupboard, like for our setup, can be preferable.
An installer will be able to find the right location for a hot water tank in your home for use with an air source heat pump to provide hot water.
While a hot water tank is typically required when using an air source heat pump to provide domestic hot water, an ASHP can be installed without a water tank but would only provide heating and another system would be required to provide hot water.
Hot Water Tank Air Source Heat Pump Type
The type of air source heat pump system used can determine whether it can work with a water tank to provide hot water.
The two main types of air source heat pumps are:
- Air to water
- Air to air
Both types extract heat from outside air but air to water heat pumps deliver that heat to water inside a home, while air to air heat pumps deliver heat into a home through air.
An air to air heat pump can’t be used to provide hot water delivered to taps and so an alternative way of providing domestic hot water will be required if using an air to air heat pump to provide heating.
A hybrid heat pump system could be used where an air to air source heat pump provides the heating and cooling, while a boiler/furnace helps provide the hot water requirements.
However, air to water heat pumps (like the one we have) can be used for domestic hot water purposes and can be used for both hot water and heating.
If looking to use an air source heat pump for hot water, then you’ll typically need to consider installing an air to water heat pump.
An air to water heat pump will therefore also need to be used alongside a hot water tank to provide hot water.
See our main article explaining air to air and air to water heat pumps for more information.
Air source heat pumps work similarly to air conditioning units and refrigerators but in reverse.
An air source heat pump sits outside of a home or building, which allows for a consistent airflow where large fans on the unit can push air into the unit, through a heat exchanger, and the heat energy stored naturally within the outside air can be captured by the refrigerant flowing through the heat pump.
As refrigerants used within air source heat pumps have low boiling points, this absorption of heat causes it to turn from a liquid to a gas.
The heated refrigerant goes through a compressor to increase the pressure of the gas, which in turn causes the temperature to increase, and helps a heat pump to deliver as much heat as possible into a home.
Typically, most air source heat pumps are set up with a buffer tank inside the home that functions as storage for hot water, used when in heating mode.
With this setup, it’s also typical for the home or building to have a separate hot water tank installed, when instant hot water for the home is required alongside heating.
See our article on how air source heat pumps work for more information.
This video below provides a great explanation for the use of a water tank with a heat pump.
When using an air source heat pump for heating or cooling purposes only, a hot water tank isn’t typically required, but another system for providing hot water will be needed.
A hybrid system approach could be used where an air source heat pump provides the heating, and a more traditional boiler or furnace system provides the hot water.
If using an air source heat pump for domestic hot water, instead of or in addition to heating, a water tank is typically required because heat pumps can’t provide hot water on demand like other traditional heating systems can.
A hot water tank will therefore need to be installed inside a home alongside the outdoor air source heat pump unit. An installer will be able to choose the right heat pump system and location for a hot water tank for your particular situation and needs.