How to improve your EPC rating

The most cost-effective improvements ranked by payback time and impact on your rating.

Improvements ranked by cost-effectiveness

The Energy Saving Trust analysed 2.4 million EPCs to identify which improvements deliver the best return on investment.¹ Here's the ranking for a typical mid-terrace house with gas central heating and a D rating:

Payback times assume current energy prices (June 2026). If gas or electricity prices rise, payback gets faster. If prices fall, it slows down.

Insulation upgrades

Loft insulation

If your loft has less than 100mm of insulation (or none at all), topping it up to 270mm is the single most cost-effective upgrade for most houses. The job is simple: rolls of mineral wool laid between and over the joists. A professional installer charges £300-£600 for a typical 3-bed semi.²

The EPC calculation assumes heat loss through the roof accounts for around 25% of a home's total heat loss. Reducing that loss by 90% (which is what 270mm of insulation achieves) can lift a D rating to a C on its own.

Cavity wall insulation

If your home was built between 1920 and 1990, it probably has cavity walls (two layers of brick with a gap between). Filling that gap with insulation beads or foam cuts heat loss through the walls by around 65%.³

Cost: £500-£1,500 depending on wall area and access. The installer drills small holes in the mortar, pumps in insulation, and re-points the holes. The job takes half a day. Not suitable for all properties (exposed locations, certain wall types). Get a survey first.

Solid wall insulation

Pre-1920 homes often have solid walls (single thickness of brick or stone). Insulating these is much more expensive: either internal insulation (lose 10cm of floor space per wall) or external insulation (cladding over the outside). Costs: £4,000-£12,000 depending on house size and method.

Solid wall insulation can lift an E to a C, but the payback is long (25+ years). Consider it if you're doing major renovation work anyway, or if you qualify for a grant (ECO4, local authority schemes).

Heating system upgrades

Boiler replacement

If your boiler is more than 15 years old, replacing it with a modern condensing boiler improves efficiency from around 70% to 90%+. That means 20% less gas used to produce the same heat.⁴

Combi boilers (heat water on demand, no tank) cost £2,000-£3,000 installed. System boilers (with a hot water cylinder) cost £2,500-£3,500. The EPC rating boost depends on what you're replacing. An old non-condensing boiler → modern condensing = +6 to +8 SAP points. A 10-year-old condensing boiler → new condensing = +2 to +3 points.

Heating controls

Adding or upgrading controls (programmable thermostat, thermostatic radiator valves, smart heating) costs £150-£400 and saves 10-15% on heating bills. The EPC impact is modest (+2 to +4 points) but the comfort improvement is significant.

Heat pumps

Air source heat pumps use electricity to extract heat from outside air. They're 3-4 times more efficient than electric heaters, so running costs can be lower than gas if you have a good electricity tariff. Upfront cost: £8,000-£14,000, minus £7,500 Boiler Upgrade Scheme grant (available until 2028).⁵

Heat pumps work best in well-insulated homes. If your property is a D or below, insulate first, then consider a heat pump. EPC impact: +10 to +18 points depending on current heating system.

Windows and doors

Replacing single glazing with double glazing across a whole house costs £4,000-£8,000. The energy saving is around £140-£220 per year for a typical 3-bed semi, giving a payback of 20-30 years. The main benefit is comfort (less draughts, warmer rooms) rather than financial return.

If you have single glazing and can't afford full replacement, secondary glazing (adding a second pane inside the existing window) costs £150-£300 per window and achieves about 60% of the benefit of full double glazing.

Renewable energy

Solar panels

A 4kWp solar PV system (12-16 panels, typical for a 3-4 bed house) costs £5,000-£7,000 installed. It generates around 3,400 kWh per year in southern England, less in the north and Scotland. If you use 40% of that power directly (running appliances during the day) and export the rest at 15p/kWh, annual benefit is around £300-£500.⁶

EPC impact: +5 to +10 points. The SAP calculation credits you for the electricity generated, even though your rating is based on heating and hot water (not plug-in appliances). This quirk means solar often pushes a C rating to a B.

Solar thermal (hot water)

Solar thermal panels heat water directly (not electricity). Cost: £3,000-£5,000. Annual saving: £60-£100. Poor payback (30+ years) unless you're replacing an electric immersion heater. EPC impact: +3 to +6 points.

Getting a new EPC after improvements

Your EPC rating doesn't update automatically. If you've made improvements, you need to book a new assessment to get a better rating on the certificate. Cost: £60-£120.

Book the assessment after all work is complete and you have evidence (photos, invoices, guarantees). The assessor will record the new features and the SAP software will recalculate the rating. If you made the improvements the previous EPC recommended, you should see a boost close to the predicted "potential rating."