Heat Pump vs Gas Boiler: Which Improves Your EPC Rating More?
Replacing your heating system is one of the biggest decisions you can make for your home's energy efficiency. This guide compares air source heat pumps and gas boilers on EPC impact, running costs, and available UK government grants.
Why Your Heating System Matters So Much for Your EPC
Space heating accounts for around 60% of total household energy use in the UK. Because of this, your heating system is one of the single largest factors in how your EPC score is calculated. The SAP (Standard Assessment Procedure) methodology — which underpins all UK EPC assessments — weights heat source efficiency heavily. Switching from an old G-rated boiler to a modern system can move a property up two full EPC bands.
But not all heating upgrades are equal. A new gas boiler and an air source heat pump can both improve your rating — but by very different amounts, and at very different costs.
Head-to-Head Comparison
| Factor | Air Source Heat Pump | New Gas Boiler (A-rated) |
|---|---|---|
| Typical installed cost | £8,000–£15,000 | £2,500–£4,000 |
| Government grant available | £7,500 (BUS scheme) | Free via ECO4 (low income) |
| EPC score improvement | +10–25 points | +3–10 points |
| Likely band change | Often 2 full bands | Up to 1 band |
| Running efficiency (CoP) | 2.5–4.0 (250–400%) | 0.89–0.93 (89–93%) |
| Annual running cost | £800–£1,600 | £900–£1,400 |
| CO₂ emissions | Very low (uses electricity) | Moderate (burns gas) |
| Future-proofing | Grid decarbonises → cheaper | Gas prices volatile |
| Disruption | High (radiator upgrades needed) | Low (like-for-like) |
| Payback period | 8–15 years (with grant) | 5–8 years |
How Air Source Heat Pumps Affect Your EPC Score
An air source heat pump (ASHP) extracts thermal energy from outdoor air and moves it into your home. For every 1 kWh of electricity it consumes, it typically delivers 2.5–4 kWh of heat — this ratio is called the Coefficient of Performance (CoP).
In SAP calculations, heat pumps score exceptionally well because they are treated as using low-carbon electricity rather than burning fossil fuels. As the UK grid becomes cleaner, the carbon rating of a heat pump improves automatically — meaning a property fitted with a heat pump today will look even better on paper in five years without any additional work.
A typical terraced house moving from an old G-rated boiler to an air source heat pump (combined with basic insulation improvements) can expect to jump from EPC band E or D to band C or even B. For landlords facing the proposed 2030 minimum C rating requirement, this single measure could achieve compliance in one step.
Important: Heat Pumps Need Insulation First
Heat pumps work at lower flow temperatures than boilers (typically 45–55°C vs 65–75°C for a boiler). This means they need larger radiators or underfloor heating, and your home must be well insulated to retain the heat. An ASHP installed in a poorly insulated property will be inefficient and expensive to run. Always insulate before (or alongside) installing a heat pump.
How a New Gas Boiler Affects Your EPC Score
A modern A-rated condensing boiler operates at 89–93% efficiency — significantly better than an old G-rated boiler at 70–78% efficiency. Replacing an old boiler will typically add 3–10 EPC points, depending on how inefficient the existing system is.
The improvement is more modest than a heat pump because gas is still a fossil fuel. SAP penalises gas use both for its carbon emissions and for its cost compared to heat-pumped electricity (which, despite higher unit prices per kWh, is used so efficiently that the overall cost per unit of heat is often comparable).
For most households not yet ready to make the leap to a heat pump, a new condensing boiler remains a sensible mid-term improvement — particularly when combined with insulation measures.
Get a Fixed-Price Boiler Quote
A new A-rated condensing boiler can cut your heating bills by up to 30%. BOXT offers fixed-price quotes online with next-day installation available.
Typical saving: £200–£350/year switching from an old G-rated boiler
Get a Fixed QuoteThe Boiler Upgrade Scheme (BUS): £7,500 Towards a Heat Pump
The Boiler Upgrade Scheme is a UK government grant programme that pays homeowners in England and Wales a fixed voucher of £7,500 towards the cost of an air source heat pump or ground source heat pump. Unlike many energy grants, it is not means-tested — any homeowner can apply, regardless of income.
Who Qualifies for the BUS?
- ✓You own the property (freehold or leasehold)
- ✓The property is in England or Wales
- ✓Any valid EPC is in place (and no outstanding recommendations for loft or cavity wall insulation that you haven't acted on)
- ✓The installer must be MCS-certified (Microgeneration Certification Scheme)
- ✓The heat pump must also be MCS-listed
How to Apply
You do not apply directly. Your MCS-certified heat pump installer applies on your behalf and deducts the £7,500 from their invoice. You simply pay the balance. The installer will ask you to confirm eligibility and sign the application. The scheme is funded until 2028 and currently has no waiting list, though installer capacity in some regions is limited.
ECO4: Free Boiler Replacement for Low-Income Households
The Energy Company Obligation (ECO4) scheme requires large energy suppliers to fund energy efficiency improvements in fuel-poor homes. If you or someone in your household receives means-tested benefits — such as Universal Credit, Pension Credit, Housing Benefit, or Income Support — you may qualify for a free or heavily subsidised new boiler.
ECO4 also covers heat pumps, loft insulation, cavity wall insulation, and solid wall insulation. Properties with an EPC rating of D or below are prioritised. Apply through your energy supplier (British Gas, EDF, E.ON, Octopus, etc.) or through the government's ECO4 helpline.
Running Costs: Which Is Cheaper Day-to-Day?
This is more nuanced than it first appears. Electricity currently costs around 24p/kWh in the UK, while gas costs around 6p/kWh. On the face of it, gas sounds cheaper. However, because a heat pump delivers 3–4 units of heat for every unit of electricity it consumes, the effective cost per unit of heat can be comparable — or lower.
| Property Type | ASHP Annual Cost | Gas Boiler Annual Cost |
|---|---|---|
| Small flat (1–2 bed) | £600–£900 | £700–£1,000 |
| Mid-terrace (3 bed) | £900–£1,300 | £900–£1,300 |
| Semi-detached (3–4 bed) | £1,100–£1,600 | £1,000–£1,500 |
| Detached house (4+ bed) | £1,400–£2,200 | £1,300–£2,000 |
Estimates based on 2024/25 Ofgem tariff cap rates. A well-insulated home with optimised heat pump settings will be at the lower end of the range.
Which Should You Choose?
Choose a Heat Pump if…
- Your home is already well insulated (or you're insulating at the same time)
- You want the largest possible EPC improvement in one step
- You want to future-proof against gas price rises
- You qualify for the £7,500 BUS grant
- You have space for an outdoor unit (garden, driveway, or side return)
- You need to meet a minimum C rating for rental compliance
Choose a New Gas Boiler if…
- Your current boiler is old, unreliable, or failing
- You need a quick, low-disruption improvement
- Your home is not well insulated yet (do insulation first, then heat pump later)
- Budget is tight and you cannot afford the net cost after the BUS grant
- Your property is a flat where outdoor unit installation isn't feasible
See Your Property's Current Rating First
Before committing to either option, check your current EPC certificate. It will tell you your existing rating and list the specific recommendations for your property — including the expected EPC improvement for each measure.
Check your EPC rating for freeFrequently Asked Questions
Will a heat pump always improve my EPC rating?
Can I get both an ECO4 grant and the Boiler Upgrade Scheme?
Do I need to upgrade my radiators for a heat pump?
Does a heat pump make noise?
Is gas being banned in UK homes?
Finance Your Home Improvements
Energy improvements like solar, insulation, and boiler replacement can cost £2,000–£15,000. Compare personal loans from top UK lenders — get a quote in minutes with no impact on your credit score.
Estimated improvement cost: Heat pump installation: £8,000–£15,000 (minus £7,500 BUS grant)
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