Do I need insulation before a heat pump? UK 2026 guide

The short version: loft insulation and cavity wall insulation are required for the BUS grant. Solid wall insulation is not — and rarely worth doing in a typical retrofit. You do not need a Passivhaus to run a heat pump; you need a sensibly-insulated home.

What the BUS grant actually requires

Ofgem's rules for the £7,500 Boiler Upgrade Scheme include "minimum insulation requirements". Specifically:

• Loft insulation if recommended on your EPC — must be installed (or you must have an exemption) before the heat pump.
• Cavity wall insulation if recommended on your EPC and your home has unfilled cavities — same rule.
• No requirement for solid wall insulation — even if your home is solid-wall (Victorian/Edwardian terrace, pre-war detached). The economics rarely justify it for a heat pump install.

The rules apply at the point your installer registers the BUS application. Your installer will check your EPC against the requirements during the quote.

Why insulation matters for heat pumps specifically

Heat pumps run at lower flow temperatures (45-50°C) than gas boilers (65-75°C). They deliver heat more slowly and steadily. If your home loses heat fast (poor insulation, single-glazed windows, draughty floorboards), the pump struggles to keep up — runs longer, draws more power, costs more.

A well-insulated home running a heat pump achieves SCOP 3.5-4.0. A poorly-insulated home with the same pump might only get SCOP 2.5, costing 30-40% more to run.

The realistic order of works

If you are starting from a typical UK home with average insulation:

1. Loft insulation (~£300-£700). Top up to 270mm depth. Do this anyway — it is the highest-impact and cheapest measure.
2. Cavity wall insulation (~£500-£1,500). Free or heavily subsidised through ECO4 if you qualify.
3. Draught-proofing (~£100-£500 DIY, more for sash window restoration). Cheap, fast, instantly noticeable.
4. Heat pump install.
5. Solid wall insulation — only if you can do it as part of a wider renovation (re-rendering, internal refit). Standalone retrofits cost £8,000-£15,000+ for diminishing returns.

Solid wall insulation — the honest assessment

External wall insulation costs £80-£150/m² fitted. A typical 3-bed terrace has ~80-100m² of external wall, so £6,400-£15,000 for a full wrap. Internal wall insulation is similar pricing but reduces room sizes.

For most homes, the running-cost saving from solid wall insulation is £150-£400/yr — a 15-30 year payback. The BUS grant maths does not require it. Walk away from any installer who insists you "need" it before they will fit your heat pump.

What "EPC Band C" actually means

You will hear the figure "Band C or above" thrown around as a heat-pump prerequisite. This is not a regulatory requirement — it is a rule of thumb for whether your home runs a heat pump efficiently. Band D-E homes can run heat pumps fine if the install is sized correctly and the basic insulation is in place.

What does change at Band C: the gap between flow temp and outside temp the pump can handle. A Band G home with a 6kW pump might struggle in January; the same home at Band D handles fine.

Quick wins before install day

• Loft hatch insulation — most lofts are insulated; the hatch is not. £20 of foam strip and self-adhesive insulation.
• Pipework lagging — exposed hot water pipes in the loft or under the floor. £30-£50.
• Letterbox brush + door seals — £30 from a hardware shop.
• Chimney balloon — £25 if you have an unused open chimney pulling cold air in.
• Smart thermostat — comes with most heat-pump installs. Set zoning correctly from day one.

The bottom line

Get loft and cavity sorted before the heat pump (legally required for BUS, cheap to do). Do not let an installer talk you into solid wall insulation as a precondition — the maths rarely supports it. Run our free pre-survey check; the report flags any insulation prerequisites for your specific property based on your EPC.