Do you need to insulate before fitting an air source heat pump?

What to know first

This summary explains what must be fixed, which insulation is worth considering and what need not hold up a well-designed heat pump.

The direct answer is no. An air source heat pump does not require a “fully insulated” home, but it does need a design based on the heat the property will lose in cold weather.

This article mainly covers air-to-water systems, which supply radiators or underfloor heating and usually hot water. Air-to-air systems deliver heated air through indoor units, so some design and grant details differ.

Is insulation required for a heat pump grant?

No. In England and Wales, the government removed the Boiler Upgrade Scheme rule that required an Energy Performance Certificate to have no outstanding loft or cavity wall insulation recommendations. Current Ofgem guidance treats efficiency work as something to consider, not a condition every applicant must complete.

A grant rule decides whether an installation may receive funding. It does not decide whether insulation would help that particular home. The installer must still assess the property and explain what work, if any, is useful.

Which work should come before the heat pump?

This hierarchy is an editorial starting point, not an official rule. The final order should reflect the building survey and the work you have firmly decided to carry out. Its factual basis is the whole-house approach recommended by Energy Saving Trust, government ventilation guidance and the room-by-room assessment used in MCS heating design.

Making a home less draughty can help, but ventilation must remain adequate. Government guidance warns that energy-efficiency work can reduce airflow and increase damp, mould or poor-air-quality risks if ventilation is ignored.

Good to know

Draught-proofing should close uncontrolled gaps, not planned ventilation. Keep trickle vents, air bricks and extractor routes clear unless a competent professional specifies an alternative.

Traditional, listed and solid-wall homes may need specialist advice. Materials and moisture behaviour vary, so generic “seal it up” recommendations can cause problems.

How does insulation change the heat-pump design?

Insulation reduces heat loss, so the heating system has less work to do to maintain the chosen indoor temperature. Ofgem says efficiency improvements can reduce running costs and improve comfort, although the result for an individual household will depend on the complete system and how the home is used.

An MCS-compliant design should use a room-by-room heat-loss calculation. It considers room size and heat escaping through walls, roof, floor, windows and air movement. The results help size the heat pump and each room’s heat emitters, such as radiators.

A poorly insulated home may need more heat output, larger radiators, extra emitters or other distribution changes. That does not prove a heat pump cannot work. It means the design must reflect the actual demand.

The calculation must also use the right future state. Definite loft insulation due before commissioning can be included once its specification is clear. Possible solid-wall insulation several years away should not be treated as though it already exists. This is a practical implication of calculating heat loss from the fabric and air-leakage characteristics used in the final design.

Expert insight

“The practical test is not whether a home is “fully insulated”. It is whether the system can meet each room’s calculated heat loss at realistic design conditions.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

Ask the installer to show the assumptions used for insulation, windows, air leakage and room temperatures. An Energy Performance Certificate is useful background, but it does not replace a property visit and room-by-room calculation.

When might insulation not justify a delay?

A whole-home retrofit can be valuable, but it is not one compulsory package. Energy Saving Trust’s February 2026 averages for a semi-detached home put loft insulation from zero to 270mm at about £900, cavity insulation at £2,700 and solid-wall insulation at £12,000–£18,000. Its average air source heat pump figure was £11,000 before funding. Quotations vary by property, specification and associated work.

A prompt loft upgrade may sensibly precede the final calculation. Delaying a suitable heat pump solely for an unplanned solid-wall project costing many thousands may be disproportionate. This is an editorial interpretation, not a rule: comfort problems, available funding, building condition or planned renovation may change the order.

The same principle applies to floors and windows. Assess the likely benefit, disruption, moisture risk and cost rather than treating every possible measure as mandatory. Energy Saving Trust recommends planning improvements as a whole while recognising that staged work is normal and that everything does not have to be completed at once.

How should you plan the work?

1. Resolve defects and ventilation questions. Identify active leaks, damp causes and safety-critical repairs. Do not assume insulation alone will cure damp.

2. Separate definite work from ideas. Record the specification and date of fabric work that will happen before commissioning.

3. Get the heating assessment. An MCS-certified installer should visit, calculate room heat losses and assess radiators, pipework, the hot-water cylinder, controls and electrical requirements.

4. Compare written proposals. Check design assumptions, emitter sizes, estimated use or bill impact, total price and exclusions. Ofgem encourages multiple quotations, while Citizens Advice recommends checking installer credentials and comparing at least three.

5. Check funding and the contract before work starts. State payment stages, responsibility for associated work and what happens if a grant voucher is refused, expires or is withdrawn. Ofgem consent to a grant application does not create or amend the private installation contract.

For Boiler Upgrade Scheme work, the installer must be MCS certified and domestic customers must be covered by an approved consumer code. The grant process does not replace the private contract. Paid services must be carried out with reasonable care and skill under the Consumer Rights Act 2015, so keep the contract, design, commissioning records, warranties and correspondence.

What funding applies across the UK?

As checked on 27 July 2026, the Boiler Upgrade Scheme in England and Wales offers £7,500 for an air-to-water heat pump and £2,500 for an eligible residential air-to-air system. A temporary £9,000 rate applies to eligible off-gas-grid properties replacing oil or liquefied petroleum gas with an air-to-water or ground source heat pump, for applications properly made from 21 July 2026 to 31 March 2027. Ofgem confirms eligibility through the installer-led process.

Scotland’s Home Energy Scotland Grant and Loan scheme offers eligible homeowners up to £7,500 grant funding for a heat pump, an optional interest-free loan and separate support for qualifying efficiency measures. Northern Ireland has different programmes, and grants are subject to available funding; check NI Energy Advice before arranging work.

Key takeaways

• Full insulation is not a universal technical or England-and-Wales grant prerequisite.

• Fix defects and protect ventilation before making the home more airtight.

• Complete suitable, straightforward insulation before or alongside design where practical.

• Base the system on a room-by-room heat-loss calculation, not the EPC letter alone.

• Tell the installer which future improvements are definite.

• Do not delay automatically for expensive deep retrofit without assessing benefit, cost and risk.

• Check current funding and grant contingencies in the contract.

Frequently asked questions