The short version
- Insulation is not a condition of the grant. The Boiler Upgrade Scheme’s insulation requirement was removed on 8 May 2024, and since 28 April 2026 you can apply without a valid EPC.
- Insulation still changes the heat loss of your home, and the heat pump must be sized to meet 100% of that heat loss. Less heat loss can mean a smaller unit, smaller radiators and a lower flow temperature.
- Loft insulation, cavity wall insulation and draught-proofing are usually quick and low in disruption. Solid wall insulation is a much bigger job and is not needed for a heat pump.
- Do the quick jobs before the heat loss survey, or tell the surveyor what you are planning, so the design can take it into account.
- A heat pump can work in a poorly insulated home if it is designed for that home’s heat loss, which often means bigger radiators.
Many people put off a heat pump because they have heard the house must be fully insulated first. That is not the rule. Here is what the rules say now, why insulation still matters, and what to do first.
Do you have to insulate before getting a heat pump?
Not for the grant, and not for the design: the heat pump is sized for your home as it is. The Boiler Upgrade Scheme used to have one. When it opened, the regulations said a property needed a valid energy performance certificate (EPC) whose recommendation report did not recommend loft insulation or cavity wall insulation, unless that insulation could not be installed for one of a short list of reasons, such as the property being listed or in a conservation area. That “insulation requirements” regulation was removed on 8 May 2024 by the Boiler Upgrade Scheme (England and Wales) (Amendment) Regulations 2024.
A second change followed. From 28 April 2026, Ofgem’s installer guidance says properties are no longer required to have a valid EPC to apply. If your home does have a valid EPC, the installer must still give its certificate number with the application. If it does not, the installer sends other evidence instead, such as a recent energy bill or fuel receipt and photos of the existing heating system, plus the number of an expired EPC if there is one.
Today, GOV.UK lists two conditions: you must own the property, and you must be replacing fossil fuel heating such as oil, gas, electric or LPG. It adds that you are still eligible if you have already had funding to make your home more energy efficient, for example by insulating it. You may be eligible for £7,500 towards an air source heat pump in England and Wales. More on our grants and rebates page. Installers must still meet the MCS standards on system design, and that is where insulation comes back in.
Why insulation still matters
A heat pump is sized from a room-by-room heat loss calculation. The MCS heat load calculator explains that heat escapes through the fabric of the building (walls, floors, ceilings, windows and doors) and through air leakage and ventilation. Insulation lowers the fabric loss; draught-proofing cuts air leakage.
That heat loss figure then drives three things:
- The size of heat pump. MIS 3005-D, the MCS heat pump design standard, says the heat pump must provide at least 100% of the calculated heat load, without help from a supplementary electric heater. More heat loss means a bigger heat pump. See what size heat pump do I need?
- Radiator sizes and flow temperature. Heat pumps run more efficiently at lower water temperatures. A room that loses less heat can be kept warm by a given radiator at a lower temperature. Our guide to new radiators for a heat pump and to flow temperature explain why that matters.
- Running costs. A home that loses less heat needs less heat putting back in, and a heat pump running at a lower flow temperature produces more heat for each unit of electricity. MCS describes lower emitter temperatures as giving higher efficiency and lower running costs.
A worked example from MCS
The MCS heat emitter guide uses one poorly insulated, single-glazed room (adapted from a CIBSE design guide and assumed to be in London) to show the effect. The improvements in its example are cavity wall insulation, A-rated double glazing, 50 mm of underfloor insulation and careful draught-proofing.
| Scenario | Room heat loss | Radiator flow temperature |
|---|---|---|
| As it is, existing radiator | 1,671 W | Over 60°C (a specialist heat pump would be needed) |
| Fabric improved, existing radiator | 976 W | 55°C |
| As it is, larger radiator | 1,671 W | 55°C |
| Fabric improved and larger radiator | 976 W | 45°C |
The improvements cut the room’s heat loss by about 42%. Either change on its own brought the flow temperature down to 55°C. Both together reached 45°C. The guide’s advice is to always consider reducing heat losses when making changes to a house. This is one example room, not a prediction for yours.
Quick, low-disruption measures: loft, cavity walls and draughts
These are usually quick, cause little mess and can be done before a heat pump survey, but they do not suit every home.
| Measure | Who does it | Watch for |
|---|---|---|
| Loft insulation | Often DIY if the loft is easy to reach, dry and not a flat roof | Damp, flat roofs and lived-in lofts need a professional |
| Cavity wall insulation | A registered installer, after a survey | Narrow or blocked cavities, exposure to driving rain, flood risk, poor brickwork |
| Draught-proofing | Often DIY; a professional for older homes with traditional features | Never block vents, airbricks, extractor fans or ventilation for gas appliances |
Loft insulation
The Energy Saving Trust says homes can lose around 25% of their heat through an uninsulated roof, and that current building regulations recommend a minimum of 270 mm of mineral wool insulation, so it is worth measuring what is already up there: many lofts have some insulation that can be topped up. Fix any damp before insulating, and take photos before and after so there is a record of what was installed.
Cavity wall insulation
The Trust says about 33% of the heat lost from an uninsulated home goes through the walls. If your house was built after the 1920s, its outside walls are probably cavity walls; homes built from the 1990s onwards generally have wall insulation already. Bricks laid lengthways in an even pattern suggest a cavity wall.
This is not a DIY job. An installer surveys first: standard cavity wall insulation suits walls with an unfilled cavity at least 50 mm wide and clear of rubble, masonry in good condition, and walls not exposed to driving rain or at risk of flooding. Any repairs to brickwork, pointing, roofs and gutters should be done first. For an average home with easy-to-reach walls, the Trust says the job usually takes about two hours.
Draught-proofing
Draughts add to the heat your heating has to replace. The Trust says draught-proofing should be straightforward if you are confident with simple DIY: strips around windows and doors, keyhole and letterbox covers, and a chimney excluder. Keep a gap under internal doors, and leave alone the vents, airbricks, extractor fans and trickle vents a home needs. If your home is already fairly airtight, more draught-proofing may increase the risk of poor air quality, so ask first.
Solid wall insulation: a much bigger job
Homes built before 1920 are more likely to have solid walls, which have no cavity to fill. They can be insulated on the outside or the inside, and both are major jobs:
- Internal wall insulation should be fitted by a professional. Rooms cannot be used during the work, skirting boards and door frames come off, and rooms lose a little floor area and need redecorating.
- External wall insulation needs a specialist installer. The Trust says it can be applied without disruption to the household, but you may need planning permission, and the roof often needs extending and rainwater pipes moving.
- Moisture. Traditional solid walls usually manage moisture well because the materials absorb and release it. The Trust warns that insulation can upset that balance, so the installer should use suitable permeable materials and finishes, and repairs come first. Get advice if your home is listed or in a conservation area.
A heat pump does not depend on solid wall insulation. If you are planning it anyway, tell the surveyor, because it changes the heat loss. See heat pumps in older houses.
What order should you do things in?
The Energy Saving Trust suggests that if you have realistic options for improving your insulation, it is worth doing it before or alongside a heat pump installation. A sensible order for most homes:
- Repairs and damp first. Damp problems should be fixed before any insulation goes in.
- The quick jobs. Draught-proofing, topping up the loft and, if a survey says the walls are suitable, cavity wall insulation.
- Decide on the big jobs. If solid wall insulation or new windows are definitely happening soon, do them first or give the surveyor the details. If not, the heat pump is designed for the house as it is.
- The heat loss survey and design. Show the surveyor evidence of insulation that is hard to see, such as photos or paperwork. The Energy Saving Trust tells installers that underfloor insulation is assumed absent on an EPC unless it has been visually verified.
- Installation. Radiators, heat pump and controls set to the design flow temperature.
Insulating heavily afterwards still lowers your heat demand, but the heat pump may then be larger than the home needs, and the Energy Saving Trust links an oversized unit with excessive cycling (switching on and off).
For an independent list of improvements, GOV.UK’s Find ways to save energy in your home service gives owners in England and Wales recommendations with estimated costs and next steps.
Can a heat pump work in a poorly insulated home?
Yes, if it is designed for that home. The Energy Saving Trust says that whether you are able to upgrade your insulation or not, your installer will design a system to match your expected heating needs. The standard requires the heat pump to cover the full calculated heat load, so a draughtier home gets a bigger heat pump rather than a cold house.
The Trust says a home with poor insulation and high heating demand is likely to need bigger radiators throughout, perhaps with an extra one here and there, and that if your installer offers to upgrade them you should say yes to avoid fuel bill surprises. Running costs will be higher than in the same house after insulation, because there is more heat to replace.
How you run it matters even more here. The Trust’s advice is to keep the heating at a steady level, bring it on earlier in the morning, and turn it down rather than off when the house is empty. See how to run a heat pump efficiently and our comparison of heat pump and gas boiler running costs.
What to ask an installer, and where ByEco stands
Whoever you speak to, ask:
- Can I see the room-by-room heat loss calculation, and which room is the worst performing?
- What U-values have you assumed for my walls, loft and floors, and what would change them?
- If I insulated the loft or the cavity walls first, how would the heat pump size and radiators change?
- Which radiators would you replace, and what flow temperature is the system designed for?
- Is the heat pump sized for my house as it is now, or for work I have told you I am planning?
We are MCS certified for air source heat pump installation (certificate IAA10330), and we apply for the £7,500 Boiler Upgrade Scheme grant on your behalf. We do not install insulation, but if you are planning some, tell us at the survey so the design can take it into account. Cost depends on the size of system your home needs, any radiator or pipework upgrades, where the outdoor unit goes, hot water and any electrical work: see heat pump costs in Manchester, our air source heat pump service, or what happens at a heat pump survey. Get in touch to book a free survey and an itemised quote. If you are happy with it, we go ahead.
Sources
Every figure on this page was checked against primary sources on 3 November 2026. Grant rules, planning rules and prices change — if you are reading this much later, verify before acting.
- legislation.gov.uk — Boiler Upgrade Scheme Regulations 2022, regulation 6 (omitted 8 May 2024)
- legislation.gov.uk — Boiler Upgrade Scheme Regulations 2022, regulation 6 as originally made
- legislation.gov.uk — S.I. 2024/524, Boiler Upgrade Scheme (England and Wales) (Amendment) Regulations 2024
- legislation.gov.uk — Boiler Upgrade Scheme Regulations 2022, regulation 5
- legislation.gov.uk — S.I. 2026/390, Boiler Upgrade Scheme (England and Wales) (Amendment) Regulations 2026
- Ofgem — Boiler Upgrade Scheme: Guidance for Installers V5.1 (2 July 2026)
- GOV.UK — Apply for the Boiler Upgrade Scheme
- GOV.UK — Apply for the Boiler Upgrade Scheme: what you can get
- GOV.UK — Apply for the Boiler Upgrade Scheme: check if you’re eligible
- GOV.UK — Find ways to save energy in your home
- MCS — MIS 3005-D:2025 Heat Pump Design Standard, Issue 2.0 (5 December 2025)
- MCS — MCS 021 Heat Emitter Guide, Issue 2.1
- MCS — Heat Load Calculator: understanding heat loss
- Energy Saving Trust — Your heat pump questions answered (updated 27 May 2026)
- Energy Saving Trust — Roof and loft insulation (updated 8 May 2026)
- Energy Saving Trust — Cavity wall insulation (updated 8 May 2026)
- Energy Saving Trust — Draught proofing (updated 20 May 2026)
- Energy Saving Trust — Solid wall insulation (updated 18 June 2026)
- Energy Saving Trust — Heat pump installer toolkit: heat loss calculations, detailed guidance
Book your free home survey
Every home is different. The cost depends on the size of system, any radiators that need upgrading, the pipework and where the outdoor unit goes. Get in touch and we will arrange a free survey of your home and give you a clear quote. If you are happy with it, we can go ahead.