Insulate Before a Heat Pump: Loft and Cavity First

Yes: if your loft or cavity walls can still be insulated, it is usually worth doing that before, or alongside, a heat pump. The Energy Saving Trust advises looking at realistic insulation improvements first, because the heat pump is designed around how much heat your home loses, and loft and cavity wall insulation are the cheapest ways to cut that loss.

It is not a condition of the grant. GOV.UK's eligibility rules for the Boiler Upgrade Scheme do not ask for an Energy Performance Certificate or for any insulation, and say you are still eligible if you have already had funding to insulate. Insulating first is about getting a system that suits your home and costs less to run.

Why does insulation matter so much for a heat pump?

A heat pump runs at lower temperatures than a gas or oil boiler, and the Energy Saving Trust says it is more than three times as efficient. To keep a home warm at those lower temperatures, the installer works out how much heat each room loses and sizes the heat pump and radiators to match.

The Trust explains what happens in a poorly insulated home: the installer designs for the higher heating demand, which often means bigger radiators throughout and sometimes extra ones. The heat pump can still heat the home, but more of what you pay goes into replacing heat that escapes. Cut the heat loss first and the design starts from a lower number.

That is why the order matters. If you insulate after the survey, the system was sized for a home that no longer exists. If you insulate before, the installer measures the home you will actually live in.

Why loft and cavity first, rather than solid walls?

Because they are the cheapest, quickest and least disruptive jobs that tackle the biggest losses. The Energy Saving Trust's figures for Great Britain:

Typical costs, checked 2 October 2026. Source: Energy Saving Trust guides to roof and loft insulation, cavity wall insulation, solid wall insulation and air source heat pumps. National averages, not a price for your home.

The Trust says cavity wall insulation will likely pay for itself in five years or less, and that loft insulation lasts around 40 years. Solid wall insulation costs far more and needs careful handling of moisture, so most people treat it as a separate decision rather than a step before a heat pump.

What should I check in the loft?

• Depth: the Trust says current building regulations recommend at least 270mm of mineral wool. Many lofts already have some, so the job is often a top-up.
• Damp: if the loft is damp, get the cause fixed first. Insulation makes the loft colder, so condensation becomes more likely.
• Ventilation: do not cover vents, grilles or airbricks.
• Pipes and tanks: once the loft is colder, pipes and tanks up there need insulating too.

If you want to keep using the loft for storage, or are weighing up rigid board against rolls, Better Lofts compares the main types of loft insulation and where each suits. Our own loft insulation guide covers costs and funding.

What should I check before filling the cavity?

Homes built after the 1920s usually have cavity walls, and homes built from the 1990s onwards usually already have wall insulation. A borescope check, your council's building control records or your EPC can tell you whether yours is filled.

The Energy Saving Trust says cavity wall insulation may not suit homes exposed to extreme weather or flooding, homes in poor condition, or cavities narrower than 50mm, and that brickwork, pointing, roofs, gutters and downpipes should be repaired first. The Trust says getting this wrong can trap damp or make the insulation fail. Cavity Wall Advice sets out the problems an unsuitable cavity fill can cause, which is worth reading before the survey. Ask for a 25-year guarantee from the Cavity Insulation Guarantee Agency (CIGA) or an independent insurance-backed one. More in our cavity wall insulation guide.

Is there funding for both?

As of 2 October 2026, GOV.UK says:

• Boiler Upgrade Scheme (England and Wales): £7,500 towards an air source or ground source heat pump. Homes not on mains gas that are heated by oil or LPG can get an extra £1,500, making £9,000, until March 2027. An MCS-certified installer applies for you, and must install the heat pump within 120 days of applying. See our heat pump funding page.
• Warm Homes: Local Grant (England): councils can fund wall, loft and underfloor insulation, air source heat pumps and solar panels for privately owned homes rated EPC D to G, where household income is usually £36,000 or less (or you get certain benefits or live in an eligible postcode). Check on GOV.UK.
• ECO4 runs until 31 December 2026; the Great British Insulation Scheme ended on 31 March 2026.
• VAT: installing insulation and heat pumps in a home is zero-rated in Great Britain until 31 March 2027, then 5%.

UK Energy Partnership is run by Better Home Hub Ltd. We are not a government body and cannot decide who gets funding. Use our grant finder as a guide, then check with the official scheme.

What if I can't insulate first?

You can still have a heat pump. The Energy Saving Trust says the installer will design the system for your home's heating needs as they are, which may mean larger radiators. If they recommend upgrading radiators, the Trust suggests saying yes to avoid surprises on your bills, and running the heating at a steady level rather than turning it up and down.

Frequently asked questions

Sources, checked 2 October 2026: GOV.UK, Boiler Upgrade Scheme (what you can get, eligibility, how to apply); GOV.UK, ECO4 extension and VAT on energy-saving materials; Energy Saving Trust, heat pump questions clarified.