Energy Saving
Insulation and Heating: Why the Two Go Together
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
The cheapest heat is the heat you don’t lose. Before spending on a new boiler or fancy controls, it’s worth knowing where your home leaks warmth — because insulation and an efficient heating system work best as a pair. Here’s where homes lose heat, and what’s worth doing.
Quick answer: A typical uninsulated home loses heat through the roof, walls, windows, floor, and draughts. The best-value fixes are usually loft insulation and draught-proofing — cheap, quick, and they make your heating work less. Cavity wall insulation, better glazing, and floor insulation cost more but help in the right home. Insulation and heating go together: seal the heat in first, and a smaller, cheaper-to-run heating setup keeps you just as warm.
Where It Goes
Where your home loses heat
Rough shares for an average uninsulated home — yours will vary, but it shows where the biggest wins usually are.
| Where | Rough share of heat lost | Best fix |
|---|---|---|
| Walls | Around 35% | Cavity or solid-wall insulation |
| Roof / loft | Around 25% | Loft insulation, topped up to ~270mm |
| Draughts & gaps | Around 15% | Draught-proofing and sealing gaps |
| Windows & doors | Around 10% | Draught-proofing first, then better glazing |
| Floor | Around 10% | Underfloor or suspended-floor insulation |
Where to Start
Quick wins and bigger jobs
Quick, cheap wins
Top up loft insulation, draught-proof doors and windows, fit a hot-water cylinder jacket, and seal gaps around pipes and skirting. These are low-cost, often DIY, and start saving straight away.
Bigger investments
Cavity or solid-wall insulation, double or triple glazing, and floor insulation cost more and take longer to pay back, but make a big difference in the right home — especially older, draughty properties.
Engineer Insight
Insulate first, then size the heating
We see it all the time: someone spends on a top-of-the-range boiler but the house still costs a fortune to heat, because the heat is pouring out through an uninsulated loft. Get the insulation right first and you often need less boiler, not more — a smaller, cheaper unit keeps a well-sealed home warm easily. Insulation also makes everything else work better: your schedule holds heat longer, and a lower flow temperature is enough to stay comfortable.
Costs
What we can help with
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Insulation & heating — your questions answered
What’s the most cost-effective insulation?
Usually loft insulation and draught-proofing. They’re cheap, quick, and cut a lot of heat loss — the roof and gaps account for a big share of what a home loses. Wall and floor insulation help more but cost more.
Does insulation reduce heating bills?
Yes, directly — the less heat your home loses, the less your boiler has to replace. Good insulation also means your heating reaches temperature faster and holds it longer, so it runs less.
How does insulation affect my heating system?
A well-insulated home needs less heat, so a smaller or lower-temperature setup keeps it comfortable. It’s why we suggest getting insulation right before sizing or replacing a boiler.
Is cavity wall insulation worth it?
In a home with unfilled cavity walls, usually yes — walls are the biggest single source of heat loss. It’s a specialist job; we can advise how it fits with your heating and refer a reputable installer.
Should I insulate before replacing my boiler?
Ideally yes. Insulating first can mean you need a smaller, cheaper boiler and lower running costs. At the very least, factor your insulation into the boiler sizing so you don’t over-spec it.
Related
Related guides
Insulation in the wider picture.
Read guideEnergy SavingBoiler Efficiency GuideInsulation lets you run cooler.
Read guideEnergy SavingLeave Heating On Low All Day?Insulation changes the answer.
Read guideSmart ControlsHow to Set Your Heating ScheduleA sealed home holds a schedule.
Read guideCentral HeatingHow Central Heating WorksWhere the heat actually goes.
Read guideMaintenanceSigns Your Boiler Needs ServicingKeep the heating side efficient too.
Read guideBrowse all Energy Saving guides, or head back to the Help & Advice Centre.
Sorted the insulation? Let’s tune the heating.
Book a service to get your boiler and controls running efficiently alongside your insulation, or call for honest advice on where to spend first. North London, upfront pricing.
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