Does a 1930s semi-detached qualify for the Boiler Upgrade Scheme?

Yes — the £7,500 BUS grant applies to any owner-occupied or privately rented property in England or Wales with a valid EPC. Cavity walls almost universal — cavity wall insulation recommendation easy to clear if not already done.

What size heat pump do I need for a 1930s semi-detached?

6–10 kW thermal output is typical, with 8 kW being the median. The exact size depends on a heat-loss calculation per BS EN 12831, which your MCS-certified installer performs on a site visit.

What pre-install work is typically needed?

Cavity wall insulation if not already present (~£500–£1,500, often free via ECO4). Loft insulation to 270 mm. An MCS-certified installer will confirm the exact scope on a site visit and price it into the quote.

Heat pump for a 1930s semi-detached: 2026 cost + sizing guide

What makes a 1930s semi-detached different

Inter-war semi-detached house with cavity walls, bay windows and typical 85–115 m² floorplate.

From a heat-pump-sizing perspective, a 1930s semi-detached has a design heat loss of 55–80 W/m² at the UK standard −2°C external design temperature (per PAS 2035). That translates to an annual space-heat demand of around 11,000–17,000 kWh and a recommended air-source heat pump capacity of 6–10 kW thermal. Smaller than gas-boiler sizing typically lands at — heat pumps run 24/7 at lower flow temperatures rather than cycling at 70°C.

Heat pump sizing + install figures — 1930s semi-detached
Parameter	Typical range	Notes
Floor area	85–115 m²	BEIS English Housing Survey median.
Design heat loss	55–80 W/m²	At −2°C external (UK design temp).
Annual heat demand	11,000–17,000 kWh	Space heating only, not DHW.
Recommended ASHP size	6–10 kW	Per BS EN 12831 sizing.
Pre-grant install cost	£10800–£16200	Including pump, cylinder, 1–3 radiator upgrades.
After BUS grant	£3300–£8700	£7,500 deducted by installer at invoice.
Common EPC band	Band D	Before retrofit work.
Typical install time	2–3 days	Whole-house including cylinder + radiator swaps.

Heat pump sizing + install figures — 1930s semi-detached— Ranges are typical for the archetype; specific quote depends on property survey by an MCS-certified installer.

BUS grant eligibility specifics for this property type

Cavity walls almost universal — cavity wall insulation recommendation easy to clear if not already done.
Side-passage often gives an ideal ASHP location with minimal sightlines from front of property.
Most 1930s semis qualify for BUS with no significant pre-install fabric work required.

Pre-install upgrades typically needed

Most 1930s semi-detacheds need some fabric or radiator work before the heat pump can be commissioned. The most common scope:

Cavity wall insulation if not already present (~£500–£1,500, often free via ECO4).
Loft insulation to 270 mm.
Radiator upgrade in 1–2 rooms (typically lounge + main bedroom).
Hot water cylinder install if currently on combi.

The full scope is set by your MCS-certified installer’s heat-loss calculation. Most installers absorb the radiator swap and cylinder install within the BUS-grant pricing — you don’t have to coordinate them separately.

Is this archetype right for you?

The single most common UK retrofit profile in 2026. Standard install, predictable cost, minimal fabric work, BUS-grant eligible without exemption paperwork.

Check your specific home

The figures above are typical for the archetype. Your specific property may sit at either end of the range depending on orientation, occupancy and prior retrofit work. Run a free Propertoasty pre-survey — combines your address, EPC and Google Solar API roof data into an installer-ready report in about five minutes.