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Hybrid heat pumps - our heating future?


Jo Alsop

Heating Hero

The Heating Hub

Jo reviews the potential for hybrid heat pumps to decarbonise heating in older and larger homes


What is a hybrid heat pump?

A hybrid heat pump is a heating system that combines an air source heat pump with a gas or oil boiler. The oil or gas boiler is used to 'top-up' a low temperature heat pump to meet the heating demands of the property where the heat pump cannot do it alone. Purpose designed hybrid systems can be set to control which heat source comes on when, depending on efficiency or energy cost targets.

How does it work?

Historically, air source heat pumps worked at lower temperatures than our gas or oil fired heating systems; commonly up to 55degC compared with 65-75degC from fossil fuel systems.

Hybrid heat pumps let the heat pump run in milder winter months. As outside temperatures dropped, and when hot water is need, the gas or oil boiler can step in to raise the temperate of the water.

A number of hybrid heat pump trials have been undertaken in existing homes to better understand the contribution a heat pump can make to a heating system. The results varied widely, which heat pumps providing between 50% and 80% of heating and hot water supplies in a sample of house types*.

However as high temperature heat pumps are now standard, so the case for hybrid heat pumps becomes less pressing, but they still may have a roll to play.

Hybrid v bivalent systems

A hybrid system is a purpose built combined heat pump with oil or gas boiler from the same manufacturer. In this set up, the heat pump can run all or most of the time and the gas or oil boiler tops it up.

A bivalent system is when any heat pump is paired with any gas or oil boiler and combined via a buffer tank. This means you can potentially work with your existing gas or oil boiler if it still in good order. In this set up, the heat pump will run as much as possible when it can meet your demand. When the outside temperature drops below a certain point the heat pump will switch off and the oil boiler will fire. I.e. they do not run at the same time.

Why do we need hybrid heat pumps?

The UK has a legal obligation to be net zero by 2050. As homes account for 19% of greenhouse gases it is important to find ways of reducing our reliance on fossil fuels. Heat pumps are widely acknowledged as the technology that will heat our homes for the coming decades

In 2019 the Committee for Climate Change (CCC) identified hybrid heat pumps as vital and fast track way to reduce our consumption of fossil fuels and begin decarbonising UK homes. They urged for the immediate deployment of hybrid heat pumps in large volumes with a target of fitting 10 million by 2035. The CCC continue to emphasise their importance in their recently published Sixth Carbon Budget.

At that time, all heat pumps were low temperature and it was argues that a heat pump could be added to an existing fossil fuel boiler without having to upsize radiators or insulate heavily. This point is largely moot as many mainstream air source heat pumps now run at 70degC as standard.

Where they may still have a role is a quick fix for smaller households with a combi boiler than will struggle to fit a hot water cylinder, although compact hot water batteries are an option here.

Where they definitely have a role is larger home with a kW capacity that exceeds a standalone heat pump (about 15kW) that does not have a 3-phase electricity supply. Hear a 15kW heat pump can run the heating most of the year and a boiler will top up the kW capacity at peak times.

Hybrid heat pump manufacturers

There are a few options for homeowners to combine a heat pump with a fossil fuel boiler and in some cases they can keep their existing boiler in place. Alternatively, any heat pump and gas or oil boiler can be combined via a buffer tank.

5kW or 8kW Altherma heat pumpVRC control with aroTHERM heat pump 5, 8, 11 and 15kW17kW Aerona R32 heat pump7.5-16kW Enviroair heat pump
33kW gas boiler or can use a third party gas boilerVaillant gas boiler or existing third party gas or oil ; boilerVortexAir Blue Flame oil boilerEnvirogreen oil boiler

Financial support

Hybrid heat pumps do not qualify for the £7.5k grant. For households with a heat requirement under 15kW it will be cheaper to fit a heat pump.

Need more help?

If you are considering a renewable technology for your home we can help. We provide impartial, expert advice for small and large projects. We will get you the right heating system and consider a full range of heat sources. Find out more about our ground-breaking services for consumers, contact us.


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* Hybrid Heat Pumps - Final report for Department for Business, Energy & Industrial Strategy - View Report