Hybrid Heat Pump Cost Calculator
Get the installed price of a hybrid heat pump (heat pump + gas boiler combo) and find out whether the lower upfront cost actually beats a full heat pump + BUS grant.
Your installation
"vs full ASHP" compares NET cost after BUS grant. Hybrid almost always loses on this metric in 2026.
What is a hybrid heat pump?
A hybrid heat pump system pairs a smaller heat pump (typically 4-6 kW) with your existing gas boiler. The heat pump handles 60-85% of your heating demand on mild days when it runs efficiently; the gas boiler kicks in for the coldest snaps and hot water peaks.
The appeal: lower upfront cost, no need to upgrade radiators (because the gas boiler can do the heavy lifting on cold days), and continued use of your existing gas connection.
Why hybrid doesn't get the £7,500 grant
From April 2023, the Boiler Upgrade Scheme stopped funding hybrid heat pumps. The government's logic: BUS is designed to phase out fossil heating, and hybrids don't actually replace the gas boiler — they keep it operating alongside a small heat pump. To meet the UK's net-zero heating goal by 2050, full heat pumps are the destination.
This is the single biggest factor in the hybrid-vs-full-ASHP decision. Without the grant, hybrid loses its main cost advantage:
| Option | Gross install | Grant | Net cost |
|---|---|---|---|
| Hybrid (4-6 kW HP + existing boiler) | £8,500 | £0 | £8,500 |
| Full ASHP (8 kW + new cylinder) | £13,500 | −£7,500 | £6,000 |
Full ASHP is £2,500 cheaper upfront after the grant, and the running cost is similar to better on Octopus Cosy. The 90% of UK homes that qualify for the BUS grant should choose full ASHP.
When does hybrid actually make sense?
There are genuine niche cases where hybrid is the right answer:
- Very large or poorly-insulated homes (250+ m², solid wall, no insulation budget) where a full heat pump would need an 18-22 kW system — gas-boiler-assisted peaks are simpler and cheaper than oversized heat pump
- Listed buildings where external heat pump units aren't allowed (planning) — a small heat pump inside + gas boiler is a workaround
- No space for a hot water cylinder — combi boilers have no cylinder; a hybrid keeps the combi and adds a heat pump for space heat only
- Tenants of unwilling landlords — DIY hybrid with a small monobloc heat pump is sometimes possible without landlord retrofit consent
- Properties not eligible for BUS (no valid EPC, won't address insulation recommendations, etc.) — once the grant is off the table, hybrid is the cheapest path to any heat pump
Hybrid running cost vs full heat pump
A hybrid running 75% heat pump / 25% gas costs ~£780/year for a typical 3-bed semi in 2026 — roughly £75 more per year than a full heat pump on Octopus Cosy. Over 15 years that's ~£1,100 extra, on top of the £2,500 upfront premium. Hybrid total disadvantage: ~£3,600 over 15 years.
Common hybrid brands & systems
- Vaillant aroTHERM Plus + ecoTec — most refined integration, single controller, ~£10,500
- Daikin Altherma 3 H Hybrid — purpose-built unit, ~£9,500
- Worcester Bosch Greenstar + heat pump — works if you have the boiler already, ~£7,500 add-on
- Mitsubishi Ecodan + any modern combi — universal, requires third-party controller, ~£8,000