Most heat pump conversations start in the wrong place. They start with which heat pump, how much it costs, and what grant is available.
Experienced architects and engineers will tell you something very different: a heat pump is only as good as the house it is installed in.
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"If you need to replace your gas boiler now, then go for a heat pump, but plan to upgrade the insulation and draught proofing of your building ASAP." Colin Usher, Retired architect and low energy house designer |
To show what that means in practice, this article follows two near-identical homes — one upgraded methodically, one left as it is. Same size, same value, very different outcomes.
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The heat pump ready series A nine-part guide to preparing your home, produced with low-carbon homes architect Colin Usher.
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Our worked example follows two near-identical homes:
At the start, both are worth £250,000, both rely on conventional heating, and both lose heat in all the usual places.
The difference is not technology. It is preparation.
If heat were money, your roof would be a wide-open wallet. In most older UK homes the loft insulation is thin, patchy or compressed, and warm air rises straight out of the house.
According to the Energy Saving Trust, a typical uninsulated home loses around 25% of its heat through the roof.
Here is what that costs. A medium-usage home uses around 9,500 kWh of gas a year, which at the current capped rate of 7.33p per kWh comes to roughly £696. Around 80% of that goes on heating, or about £557. If a quarter of it escapes through the roof, that is around £140 a year going straight through the ceiling.
Heat pumps work best when heat loss is slow, the building stays warm for longer, and the system does not have to chase temperature drops.
Roof insulation is usually the cheapest and fastest improvement you can make. Our guide to floor and loft insulation covers how much is enough — and why more is not always better.
Upgrading windows and doors is not simply a question of double versus triple glazing. The real issues are poor seals, gaps around frames, and cold surfaces that create draughts and discomfort.
Get these right and you reduce heat loss while making rooms feel warmer, even at lower thermostat settings.
That matters more than it sounds, because heat pumps run cooler than boilers. Comfort matters more than raw heat output.
Repair is often as effective as replacement. See our guide to improving windows and doors.
One of the most important factors in heat pump performance is uncontrolled air leakage. Heat escapes through chimneys, letterboxes, doors and windows, and floor gaps.
These draughts waste energy, make rooms feel cold even when heated, and force the heating system to work harder.
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The key point A heat-pump-ready home is not sealed shut. It is sealed properly. Air still needs to move through the building, just slowly and in controlled places rather than wherever it happens to leak. |
This is why ventilation belongs alongside draught-proofing rather than after it. Sealing a home without giving moisture a controlled way out can create damp problems that were not there before. Our guide to draught proofing your home covers how to find the leaks and how to keep the air healthy once they are sealed.
Floors are often ignored because they are awkward and unseen. But suspended timber floors in particular allow cold air to circulate, causing significant heat loss along with cold feet and draughts.
Insulating beneath the ground floor dramatically reduces heat loss — especially important when switching to low-temperature heating.
Not every fix needs to be a major job. A good quality underlay beneath a carpet, taped around the edges and junctions with vapour tape, both insulates and seals the draughts coming up between the boards. For a room whose carpet is due for replacement anyway, this costs very little.
Where you can get beneath the floorboards, fitting insulation between the joists delivers considerably more. Full detail in our guide to floor and loft insulation.
Walls are where retrofit becomes more complex, and where the impact on heat loss is largest. The average UK home loses around 33% of its heat through external walls.
In Colin's house, the approach was targeted rather than total:
This is a crucial lesson. You do not need to do everything at once. Targeted wall insulation reduces heat loss, improves comfort, and makes future upgrades easier.
It also avoids a common mistake: installing a heat pump before dealing with the biggest heat-loss surfaces. Our guide to wall insulation options compares cavity, external and internal insulation.
If you are planning an extension anyway, use it. A well-designed, low-energy extension can add space without substantially increasing heat demand, and can improve the performance of the whole house.
Poorly designed features work the other way. Roof windows in the wrong place can cause overheating, increase energy use, and work against heat pump performance.
Orientation is the thing to get right:
The same building work costs roughly the same either way. Getting the design right is what separates an extension that helps from one that quietly adds to your bills for the next thirty years.
This is the moment the whole story has been building towards.
After insulation, draught-proofing, floor upgrades and wall improvements, when Colin's boiler finally fails, he is ready. Not rushed, not panicked, and not installing a heat pump into a leaky building.
At that point:
Kelvin, meanwhile, replaces a failed boiler in an emergency — on whatever terms are available that week, into a house that has not changed.
Before you get quotes, our guide to assessing your home for heat pumps covers what to check and what to ask an installer.
Solar works best when your home already uses energy efficiently, electricity demand is lower and steadier, and a heat pump can soak up daytime generation.
It is a bonus, not a fix for poor fabric. Panels on a leaky house generate electricity that then leaks out as heat.
See our guides to solar panels and heat pumps and home batteries.
In our worked example, the total investment across the whole programme is around £54,500, covering:
| Before | After | |
|---|---|---|
| Property value | £250,000 | £285,000 |
| Annual energy saving | — | Around £1,800 a year |
| Comfort | Cold spots, draughts | Significantly improved |
[EDITOR — these figures need substantiation and a source before publication. See notes.]
This is not about quick payback alone. It is about a warmer home, lower bills, future-proofing, and reduced carbon emissions.
There is help available towards the cost of both the heat pump and the fabric improvements that come first.
Grant schemes and eligibility change regularly. Check the current position on gov.uk before relying on any of them. Correct as of August 2026.
It is not a legal requirement, and insulation is no longer a condition of the Boiler Upgrade Scheme. But the better insulated your home, the more efficiently the heat pump runs, the lower your bills, and the smaller and cheaper a unit you may need.
Insulation first, airtightness second, ventilation third, heat pump last. Within insulation, start with the roof — it is the cheapest improvement and a typical uninsulated home loses around a quarter of its heat that way.
Yes, and most households do. Targeted improvements — one wall, one side of the house, one room's flooring — reduce heat loss immediately and make later upgrades easier. Doing everything in one go delivers the best results but is not realistic for most budgets.
It will work, but it will work harder. A heat pump in a leaky building runs at maximum power more of the time, costs more to run, and needs to be a larger and more expensive unit. That is the difference between the two houses in this article.
The Energy Saving Trust estimates a typical uninsulated home loses around 25% of its heat through the roof and around 33% through external walls. Both figures depend heavily on the construction and condition of the individual property.
Solar works best once the fabric is sorted and demand is lower and steadier, and a heat pump can make good use of daytime generation. It is a bonus rather than a substitute for insulation — panels on a poorly insulated house generate electricity that then escapes as heat.
Heat pumps are not a silver bullet. But installed into a properly prepared home, they work extremely well.
The mistake many households make is starting with the technology instead of the building.
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The order that matters Insulation first. |
That is how you make a home truly heat pump ready.
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Next in this series 2. Assessing Your Home for Heat Pumps: What to Check Before Installation — how to survey your own home, and the questions to ask an installer before you commit. |
Produced with Colin Usher, low-carbon homes architect. Last updated: 3 August 2026.
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