The short answer
A full heat pump meets all of your heating and hot water from the heat pump alone. A hybrid system pairs a heat pump with a back-up boiler (usually gas) — the heat pump handles most of the year, and the boiler tops up on the coldest days or for fast hot water. A full system delivers the lowest carbon and lowest running cost when the home is suitable, and it qualifies for the £7,500 Boiler Upgrade Scheme grant. A hybrid keeps a fossil-fuel boiler, so it has higher emissions, but it can suit hard-to-treat homes where a heat pump alone would struggle, or as a stepping stone. Note that a hybrid is generally not eligible for the Boiler Upgrade Scheme, which funds heat pumps that meet the property's full heat demand. For most homes that can take it, a correctly sized full heat pump is the better long-term option.
If a full heat pump feels like a stretch for an older property, a hybrid is often suggested. Here is how the two approaches compare and where each fits.
Hybrid vs full heat pump
- Full system heat sourceHeat pump only
- Hybrid heat sourceHeat pump + back-up boiler
- CarbonFull: lowest; hybrid: higher
- BUS grantFull: £7,500; hybrid: generally not eligible
- Best forFull: suitable homes; hybrid: hard-to-treat
How each system works
A full heat pump is sized to meet the home's entire heat loss, so it covers space heating and hot water on its own across the year, including the coldest weather. This requires the property to be reasonably well insulated and to have radiators or underfloor heating sized for the heat pump's lower flow temperature.
A hybrid keeps an existing or new boiler alongside the heat pump. Controls decide which heat source to use: the heat pump runs for the bulk of the year when it is most efficient, and the boiler steps in during peak cold or for rapid hot-water recovery. This means the heat pump can be smaller and the home does not have to be optimised purely around it.
| Factor | Full heat pump | Hybrid (heat pump + boiler) |
|---|---|---|
| Heat sources | Heat pump only | Heat pump + boiler |
| Carbon emissions | Lowest | Higher (boiler still burns fuel) |
| Running cost | Lowest when home is suitable | Mixed; depends on boiler use |
| Suits hard-to-treat homes | Needs upgrades first | Yes, with less upfront work |
| BUS grant | £7,500 | Generally not eligible |
| Long-term direction | Fully electrified | Still tied to a fossil boiler |
Indicative comparison for guidance. Sources: Energy Saving Trust; Ofgem; Nesta.
Cost, carbon and grants
A full heat pump gives the lowest carbon footprint because it removes fossil-fuel combustion entirely, and its emissions keep falling as the electricity grid decarbonises. It is also eligible for the £7,500 Boiler Upgrade Scheme grant, which substantially offsets the install cost.
A hybrid retains a fossil-fuel boiler, so some combustion — and some carbon — remains. Crucially, hybrids are generally not eligible for the Boiler Upgrade Scheme, which is designed to fund heat pumps that meet a property's full heating demand. That removes a major financial incentive and changes the cost comparison.
Controls, complexity and maintenance
A hybrid is a more complex system than either a full heat pump or a standalone boiler, because it has two heat sources and a controller deciding between them. That controller uses logic — often based on outdoor temperature, the relative cost of electricity and gas, or a target efficiency — to choose the heat pump or the boiler at any moment. Set up well, this captures the heat pump's efficiency for most of the year while keeping the boiler in reserve for peak cold.
The trade-off is more equipment to install, maintain and eventually replace: an outdoor heat pump, a boiler, a cylinder in many cases, and the integration controls. You keep a gas (or oil) supply, a flue and annual boiler servicing alongside the heat pump's own maintenance. A full heat pump removes the boiler, flue and fuel supply entirely, simplifying the system and reducing the number of things that can need servicing.
It is also worth checking how the controls prioritise the heat pump. A poorly configured hybrid can lean on the boiler more than it should, eroding the carbon and running-cost benefit. A competent installer commissions the controls so the heat pump leads and the boiler only supplements.
When a hybrid makes sense
A hybrid is worth considering for genuinely hard-to-treat homes — a poorly insulated solid-wall property with small radiators, where bringing it up to full-heat-pump standard would be costly or impractical. The back-up boiler covers the coldest snaps, so the heat pump does not have to handle the full peak load, and the home can still cut emissions substantially for most of the year.
It can also act as a transitional step: install the heat pump now, run it as the lead source, and remove reliance on the boiler over time as insulation and radiators are upgraded. For most homes that can reasonably accommodate a correctly sized full heat pump, though, the full system is the stronger long-term choice on carbon, running cost and grant eligibility. An MCS-certified installer's heat loss survey is the right way to decide which path fits your property.
Frequently asked questions
Can I get the £7,500 grant for a hybrid heat pump?
Generally no. The Boiler Upgrade Scheme is designed to fund heat pumps that meet the property's full space-heating and hot-water demand, so hybrid systems that retain a fossil-fuel boiler are typically not eligible. A full heat pump is the route to the £7,500 grant, subject to the EPC requirement and an MCS-certified install.
Is a hybrid better for an old, poorly insulated house?
It can be a pragmatic option. In a hard-to-treat home where a full heat pump would need extensive insulation and radiator upgrades, a hybrid lets the heat pump cover most of the year while the back-up boiler handles peak cold. It cuts emissions without the full upgrade, though it keeps a fossil boiler and misses the grant.
Does a hybrid save carbon compared with a gas boiler?
Yes, usually. The heat pump does most of the heating across the year, so a hybrid emits less than a standalone gas boiler. But it still burns fuel during peak demand, so its carbon savings are smaller than a full heat pump, which removes combustion entirely.
Sources & further reading
- Energy Saving Trust — air source heat pumps
- Ofgem — Boiler Upgrade Scheme eligibility
- Nesta — heat pumps and home suitability
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.