Most homeowners assume that insulation is the biggest factor in their EPC rating.
In reality, your heating system usually has a greater impact on your EPC score than your walls, loft, or windows.
Here’s why — and how you can use this to your advantage.
Why Heating Carries More Weight in EPC Calculations
EPCs are generated using the government’s SAP (Standard Assessment Procedure) model.
SAP heavily prioritises:
Fuel type (gas, electricity, oil, LPG, renewable)
Boiler efficiency and age
Heating controls (thermostats, zoning, programmers)
Heat distribution losses
Carbon emissions
Insulation matters — but heating defines how much energy is burned every year, which is the core of the EPC calculation.
This means:
Changing your heating system can shift your EPC band faster than insulating your entire home.
Example: Small Heating Change, Big EPC Jump
| Upgrade | Typical EPC Impact |
|---|---|
| Old G-rated boiler → modern condensing boiler | +8 to +15 points |
| Add smart heating controls | +2 to +5 points |
| Switch from electric resistance heating to gas | +10 to +20 points |
| Add cavity wall insulation | +4 to +8 points |
| Add loft insulation | +2 to +6 points |
In many cases, one boiler upgrade equals the impact of multiple insulation upgrades combined.
Why Insulation Sometimes Delivers Less EPC Benefit Than Expected
Insulation:
Reduces heat loss ✔
Improves comfort ✔
Lowers bills ✔
But in SAP:
Insulation has diminishing returns
After basic levels are met, additional insulation adds fewer points
Older homes may be capped by construction type
So while insulation is important, it often cannot overcome a poor heating profile.
The Three Heating Factors That Matter Most
1. Boiler Efficiency Rating
A 15-year-old non-condensing boiler is a major EPC penalty.
2. Fuel Type
Electric resistance heating and oil score poorly. Gas and renewables score better.
3. Controls and Zoning
Room thermostats, programmers, TRVs, and smart controls all improve your EPC.
Strategic EPC Upgrade Order (Best ROI)
Upgrade boiler if old or inefficient
Add or modernise heating controls
Optimise fuel type if feasible
Improve insulation where cost-effective
This sequence usually produces the largest EPC gain per pound spent.
Why This Matters When Selling or Renting
Your EPC directly affects:
Buyer perception
Mortgage eligibility
Rental compliance (minimum band rules)
Negotiation power
If your EPC is low because of heating — not insulation — fixing the wrong thing wastes money and time.
Before spending thousands, speak with a qualified EPC Assessor in London who can interpret your specific report.
What EPCrate Recommends
EPCrate advises homeowners to:
Review their heating system first
Model upgrade impact before installing anything
Avoid blanket “insulate everything” approaches
You can book an EPC assessment to understand exactly what’s dragging your score down.
See transparent pricing or learn more about the company on the About Us page.
Questions? The team is available via the Contact page.
Final Takeaway
Insulation improves comfort.
Heating defines efficiency.
If your goal is to raise your EPC rating quickly and cost-effectively, your heating system is almost always the smartest place to start.
If you own or manage a listed building and want clarity on EPC requirements, get expert advice before assuming exemption or investing in upgrades.
Address: 150–160 City Road, London, EC1V 2NX
Phone: 020 3488 4142
Email: info@epcrate.co.uk
