Air source heat pumps are electrical appliances that transfer heat from the outside of a home to provide heating throughout the colder months.
They can also either be used for cooling a home in the warmer months or for providing domestic hot water.
However, as air source heat pumps can become increasingly less efficient at temperatures below freezing, it can sometimes make sense to install a hybrid heat pump system where a heat pump is combined with another heating system to help mitigate the downsides of a standalone heat pump.
A hybrid air source heat pump is a system that uses both an air source heat pump and a gas or oil boiler/furnace to provide heating or hot water. This may be required in cases where a heat pump alone cannot meet heating or hot water demands, or when outside air temperatures can get too cold.
Our home is only served by an air source heat pump for heating and hot water, and we don’t have any other system installed.
In many cases a single air source heat pump like ours can be sufficient for everyday needs.
However, in some situations is can be more suitable to pair an air source heat pump (ASHP) with another system such as an oil or gas boiler/furnace, therefore creating a hybrid heat pump (HHP) system where either one could be used depending on the requirements at the time.
In this article we cover more about hybrid air source heat pump systems, explaining how our ASHP system is setup and in what scenarios you would consider a hybrid system.
A hybrid air source heat pump system consists of two separate units; an air source heat pump and a fossil fuel boiler or furnace, both of which combined are used to heat a home, and provide domestic hot water if required and with the right setup.
An air source heat pump works by transferring heat energy from outside air into a home, while a boiler or furnace uses the combustion of fossil fuels (such as natural gas, oil or propane) to produce heat.
The two units could work together to provide heating for your home. One of the main reasons why an air source heat pump would be paired with an additional heating system would be that ASHPs deliver lower temperature heat than other conventional heating systems.
An air to water heat pump typically provides output water temperatures up to 45°C (113°F), while a boiler or furnace can typically generate higher water temperatures of up to 75°C (167°F).
In the UK, BS EN14511 specifies a flow temperature of 45°C (113°F) and a return flow temperature of 40°C (104°F).
At these temperatures an ASHP can be at its most efficient because the temperature difference between the outside air and indoors remains lower.
At higher output temperatures than this, an air source heat pump can be less efficient because more power input can be required to increase water temperatures further.
Our air source heat pump can have a maximum outlet water temperature of 60°C (140°F), but COP (Coefficient of Performance) can be reduced at this maximum temperature.
Our heat pump runs at a nominal water heat output of 35°C (140°F) to help it be as efficient as possible.
Air source heat pumps can also be affected by sub-zero temperatures because there’s less heat energy within the air as temperatures drop.
This means that ASHPs can become more costly to run at very low temperatures and output temperatures can also be affected.
For example, our heat pump can work down to -20°C (-4°F).
The graph below shows how the output temperature from our heat pump falls as temperatures fall below freezing.
In summary, this means that air source heat pumps are more suited to lower heating temperatures and should therefore be used with large surface area heating appliances such as underfloor heating and modern radiators.
Our air source heat pump system uses underfloor heating on the lower floor and radiators on the upper floor.
Air source heat pumps can therefore struggle in very low temperatures but another heating system such as a gas boiler won’t typically be affected by such cold temperatures.
A hybrid system can therefore in certain situations be more efficient than either a heat pump or boiler alone. By using both a heat pump and boiler, you can take advantage of their individual strengths to create a more efficient overall system.
For example, a boiler/furnace can be more efficient than the heat pump at lower outside temperatures or when demand for very hot water is increased, and so it can take over from a heat pump in these scenarios.
This could result in a system that can heat your home more efficiently than a heat pump or boiler alone, potentially saving you money on your energy bills.
The following YouTube video describes the operation of a typical hybrid air source heat pump system:
When A Hybrid Heat Pump Might Be Required
- You live in a climate with extreme temperatures. As hybrid heat pumps can use both an air source and a boiler or furnace, they can effectively heat homes in a wider range of climates. If you live in an area with freezing winters, a hybrid heat pump can help keep your home more comfortable.
- You have a high electricity energy costs. If your electricity bill is higher than you’d like, a hybrid heat pump could help you save money. Gas boilers will typically use less electricity than traditional heat pumps and so a hybrid system could work to help keep running costs as low as possible.
- You want a backup heating system. If you’re looking for a heating system with a backup, a hybrid heat pump is a good option. As boiler technology is more commonplace than ASHP technology, a backup boiler could provide peace of mind if there’s an issue with the heat pump.
- Required to meet decarbonization challenges. A study on hybrid heat pumps undertaken for the Department for Business, Energy & Industrial Strategy aimed at advancing the understanding their potential role in the decarbonization of domestic heat suggests that a hybrid heat pump solution could help overcome the challenge of high costs associated with reinforcing electric distribution networks to deal with heating provided in homes by electrical energy only.
- High user demand for hot water. As air source heat pumps work at lower output temperatures, they can’t provide hot water on demand like a combi boiler can and so must be paired with a hot water tank. In times of high user demand a hybrid heat pump system could help meet the demand.
A hybrid air source heat pump can be worth it when the demand for heating and/or hot water can outweigh the supply provided by an air source heat pump alone.
Not only that, but hybrid air-source heat pumps offer other benefits as well. Here’s a rundown of three other advantages of these systems:
- Hybrid heat pumps are more versatile than traditional heat pumps. As they can use both an air source heat pump and a boiler/furnace, they can be used in a wider range of climates and homes.
- Hybrid heat pumps offer greater comfort than traditional heat pumps. As they can maintain a more consistent heating and hot water temperature, they can help make your home more comfortable.
- Hybrid heat pumps are more durable than traditional heat pumps. Because they have two units, if one unit breaks down, the other can keep your home providing with heating or hot water.
A downside to hybrid heat pumps is that they can be more expensive to install than standalone heat pumps.
However, the initial investment is typically offset by the savings you’ll see on your energy bills. If you’re looking for an efficient and effective way to heat your home, a hybrid heat pump can be worth considering.
A hybrid heat pump can be a more efficient and effective way to heat your home in certain scenarios, such as when demand for very hot water is high or when outdoor air temperatures are very low.
If you’re looking for a heating system that could save you money on your energy bills and provide heating or hot water no matter the demand, a hybrid heat pump can be worth considering.
These systems are more versatile than traditional heat pumps and can offer greater comfort and durability. Speak to a local installer for advice on hybrid heat pump systems and how one could be implemented into your home.