If you like the idea of an air source heat pump but aren’t ready to give up your gas boiler, a hybrid heat pump system might be worth a look. It pairs the two together, using the heat pump as the default heat source and calling on the boiler when conditions demand it. For homeowners with insulation that isn’t quite up to standard, or those who want to reduce gas use gradually, this can feel like a sensible middle ground.
However, it isn’t automatically the cheaper option. In fact, it only works well when it’s designed properly. So, here’s how it works, and how to tell if it suits your home.
How a Hybrid Heat Pump System Actually Works
A hybrid heat pump system connects an air-to-water heat pump and your existing gas boiler to the same wet central heating system, using a hybrid controller to decide which one runs at any given time. The heat pump extracts warmth from outdoor air and transfers it into water circulating through your radiators or underfloor heating. It typically handles day-to-day heating during mild weather, while the boiler steps in for high demand, rapid warm-up, or hot water.
The temperature or condition at which a bivalent heating system switches from heat pump to boiler is known as the system’s bivalent point. This isn’t a fixed number like zero degrees, whatever some suppliers might suggest. It depends on your property’s heat loss, the heat pump’s output, your radiator temperatures, and how your controls are set up, so getting it right takes proper assessment rather than guesswork or a rule of thumb.
Why Homeowners Choose to Keep the Boiler
Retaining the boiler solves practical problems that a full conversion can raise, which is why a heat pump with gas boiler setup appeals to many households. We covered these trade-offs in our air source heat pumps vs gas boilers guide, but the main reasons tend to be:
- Instant Hot Water: A combi boiler keeps providing hot water on demand, avoiding a cylinder if there’s nowhere suitable to put one.
- Peak Heating Demand: Heat pumps work best running steadily at lower temperatures, so the boiler covers cold mornings or a quick recovery.
- Heat Pump Backup Heating: If the heat pump is ever unavailable, the boiler gives you a reliable fallback.
- Lower Disruption: Keeping parts of the existing system can mean less upheaval than a full replacement.
Among the hybrid heating benefits homeowners value most is this flexibility, using the heat pump when it makes sense without losing what already works.
What a Hybrid System Costs to Run and Install
A hybrid heat pump system generally costs £4,000 to £10,000 to install, depending on the size of the heat pump, any radiator changes, and labour [1]. That’s a broad guide rather than a quote.
Running costs come down to comparing the price of a kilowatt-hour of useful heat from each source. Using illustrative figures of 30p per kWh for electricity and 7p per kWh for gas, with a boiler at 90% efficiency and a heat pump achieving a seasonal performance factor of 3.0, the heat pump would cost around 10p per kWh of heat against roughly 7.8p for the boiler. In that scenario, gas works out cheaper, even though the heat pump is more efficient overall.
The hybrid heat pump cost only tips in the heat pump’s favour if electricity prices fall, gas rises, or the heat pump performs better than assumed, so ask your installer to show their working.
Is a Hybrid System Right for a Poorly Insulated Home?
A hybrid system tends to cope better with a high heat loss property than a standalone low temperature heat pump would, because the boiler can pick up the peak demand the heat pump struggles with. That doesn’t mean insulation stops mattering. Poor insulation still means your home needs more heat throughout the season, and your heat pump may need to run longer and at higher flow temperatures, which can affect its efficiency.
Even so, a retrofit hybrid system can be a reasonable option where full insulation work isn’t affordable right away, or where external wall insulation simply isn’t practical given the building’s construction.
The sensible approach is usually fabric first where you can manage it, hybrid second. Loft insulation, draught reduction, and better glazing all reduce hybrid heat pump costs over time by cutting the size of heat pump you need and easing the load on both heat sources.
Getting the Design Right: Sizing, Radiators and Controls
A well-designed hybrid heat pump system starts with a proper room-by-room heat loss calculation, not simply matching the new heat pump to your old boiler’s output. Since 2024, MCS guidance has required the heat pump to meet at least 55% of the calculated heat load at a 55°C flow temperature, with controls capable of prioritising the heat pump over the boiler [2].
Your existing radiators may still work, but they’ll usually deliver less heat at the lower flow temperatures a heat pump prefers compared with a traditional boiler. We’ve written previously about getting radiator performance right for heat pump systems, which is worth a read if you’re weighing up whether yours will need upgrading.
A retrofit hybrid system doesn’t necessarily mean replacing every radiator, but your installer should identify which rooms fall short and explain what that means in practice, alongside confirming the bivalent heating system’s proposed switch-over point for your property.
Grants, Planning and What to Ask Your Installer
Worth being clear about: the Boiler Upgrade Scheme does not cover a hybrid heat pump system. Ofgem’s guidance is explicit that a heat pump with gas boiler setup is excluded from BUS funding, even though a standalone heat pump would qualify [3]. We’ve explained the grant landscape in our air source heat pump grants guide, a useful next step once you’ve decided which route suits you. Planning rules vary by property type, so confirm this early rather than assuming.
Before choosing an installer, it’s worth asking:
- What is the calculated heat loss for each room in the property?
- What percentage of the design heat load will the heat pump be expected to meet?
- What is the proposed bivalent point, and what’s the reasoning behind it?
- Which gas and electricity prices were used to calculate expected running costs?
- Is the installer MCS certified, and is the proposed system fully compliant?
Get a Straight Answer on Whether Hybrid Heating Suits Your Home
At SESC Solutions, we’re a family-run team with over thirty years of experience across electrical, plumbing, heating, and renewables, working across Dorset, Hampshire, Somerset, and Wiltshire. Our engineers are fully qualified, DBS checked, and MCS registered, so you get an honest assessment of whether a hybrid system, a standalone heat pump, or your existing boiler suits your home best.
Call us on 01747 445 509 or fill in our contact form to arrange a proper survey of your property.
External Sources
[1] Housey, ‘Hybrid Heat Pump System Installation Costs in the UK’: https://www.housey.co.uk/knowledge-base/hybrid-heat-pump-system-installation-costs-uk
[2] MCS, ‘MCS Has Published an Updated Version of MIS 3005-D: The Heat Pump Design Standard’: https://mcscertified.com/mcs-has-published-an-updated-version-of-mis-3005-d-the-heat-pump-design-standard/
[3] Ofgem, ‘Boiler Upgrade Scheme (BUS)’: https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/boiler-upgrade-scheme-bus-property-owners
