Air Source Heat Pumps for London Homes: Installation, Grants and Costs 2025

AN AIR SOURCE HEAT PUMP (ASHP) EXTRACTS LATENT HEAT FROM OUTSIDE AIR EVEN AT TEMPERATURES AS LOW AS -20°C AND COMPRESSES IT TO RAISE ITS TEMPERATURE TO HEAT WATER FOR SPACE HEATING AND DOMESTIC HOT WATER (DHW). THE EFFICIENCY OF AN ASHP IS MEASURED BY ITS COEFFICIENT OF PERFORMANCE (COP) — THE RATIO OF HEAT OUTPUT TO ELECTRICAL INPUT. A TYPICAL UK ASHP ACHIEVES A SEASONAL COP (SCOP) OF 2.5-4.0, MEANING FOR EVERY 1KW OF ELECTRICITY INPUT, IT DELIVERS 2.5-4.0KW OF HEAT. THIS MAKES ASHPS FAR MORE EFFICIENT THAN ELECTRIC RESISTANCE HEATERS (COP 1.0) AND EVEN GAS BOILERS (EFFICIENCY APPROXIMATELY 89-93% CONDENSING). WHY ASHPS MATTER FOR LONDON HOMES: GAS BOILER BAN — FROM 2035, NEW GAS BOILERS WILL NOT BE PERMITTED IN NEW UK HOMES (LONDON INCLUDES); THE REPLACEMENT OF GAS BOILERS WITH HEAT PUMPS IN THE EXISTING LONDON HOUSING STOCK IS CENTRAL TO THE UK'S NET ZERO STRATEGY; THE BOILER UPGRADE SCHEME (BUS) £7,500 GRANT WAS RENEWED AND IS AVAILABLE IN 2025 TO SUPPORT LONDON HOMEOWNERS MAKING THE SWITCH; LONDON CARBON REDUCTION TARGETS — THE MAYOR OF LONDON HAS COMMITTED LONDON TO ZERO CARBON BY 2030 FOR THE GLA-CONTROLLED ESTATE AND SUPPORTS THE NATIONAL NET ZERO TARGET FOR LONDON'S WIDER HOUSING STOCK; EPC IMPROVEMENT — REPLACING A GAS BOILER WITH AN ASHP IN A LONDON HOME TYPICALLY IMPROVES THE EPC RATING (SAP SCORE) SIGNIFICANTLY, AS THE SAP ALGORITHM REFLECTS THE LOWER CARBON INTENSITY OF ELECTRICITY VERSUS GAS.

NOT ALL LONDON HOMES ARE IMMEDIATELY SUITABLE FOR ASHP INSTALLATION WITHOUT MODIFICATIONS. THE KEY SUITABILITY FACTORS FOR LONDON HOMES: INSULATION — ASHPS DELIVER HEAT AT LOWER FLOW TEMPERATURES THAN GAS BOILERS (TYPICALLY 35-55°C VERSUS 60-80°C FOR GAS); TO HEAT A LONDON HOME EFFECTIVELY AT THESE LOWER FLOW TEMPERATURES, THE HOME MUST BE WELL INSULATED; A LONDON VICTORIAN TERRACE WITH ORIGINAL SINGLE-GLAZED WINDOWS, NO CAVITY WALL INSULATION AND NO LOFT INSULATION IS LIKELY TO NEED INSULATION IMPROVEMENTS BEFORE AN ASHP WILL WORK EFFICIENTLY; PAS 2035 ASSESSMENT — WHERE GOVERNMENT FUNDING IS USED (BUS GRANT), A PAS 2035 ASSESSMENT BY AN ACCREDITED RETROFIT ASSESSOR IS REQUIRED; THIS IDENTIFIES INSULATION IMPROVEMENTS NEEDED ALONGSIDE THE ASHP; RADIATORS — EXISTING RADIATORS IN MOST LONDON HOMES WERE SIZED FOR 70-80°C FLOW TEMPERATURES FROM A GAS BOILER; AT THE LOWER FLOW TEMPERATURES OF AN ASHP (35-55°C), EXISTING RADIATORS MAY NOT EMIT SUFFICIENT HEAT; RADIATOR UPGRADES (LARGER RADIATORS, ADDITIONAL RADIATORS, OR LOW-TEMPERATURE RADIATORS SUCH AS STELRAD COMPACT PLUS OR PURMO VENTIL COMPACT) ARE OFTEN REQUIRED AS PART OF A LONDON ASHP INSTALLATION; UNDERFLOOR HEATING COMPATIBILITY — LONDON HOMES WITH EXISTING WET UNDERFLOOR HEATING ARE HIGHLY COMPATIBLE WITH ASHP, AS UFH OPERATES AT 30-50°C FLOW TEMPERATURES — THE SWEET SPOT FOR HEAT PUMP EFFICIENCY; OUTDOOR UNIT PLANNING PERMISSION — IN LONDON, ASHP OUTDOOR UNITS BENEFIT FROM PERMITTED DEVELOPMENT (PD) RIGHTS PROVIDED THEY MEET THE CONDITIONS OF CLASS G OF THE GPDO 2015 (NOT IN FRONT OF THE PRINCIPAL ELEVATION, NOT IN A CONSERVATION AREA, BELOW CERTAIN NOISE THRESHOLDS MEETING MCS 020 STANDARD); IN LONDON CONSERVATION AREAS, PLANNING PERMISSION MAY BE REQUIRED FOR THE OUTDOOR UNIT.

THE MOST INSTALLED AND SPECIFIED AIR SOURCE HEAT PUMP BRANDS FOR LONDON RESIDENTIAL PROPERTIES IN 2025: VAILLANT AROTHERM PLUS — THE MOST INSTALLED RESIDENTIAL ASHP BRAND IN THE UK IN 2024-2025; AVAILABLE IN 5KW, 7KW, 10KW AND 12KW OUTPUT AT A7/W35 TEST CONDITIONS; THE AROTHERM PLUS 7KW IS THE MOST APPROPRIATE FOR A TYPICAL LONDON 3-BED TERRACE WITH MODEST INSULATION IMPROVEMENTS; KEY FEATURE: OPERATES DOWN TO -20°C AMBIENT TEMPERATURE; A++ ENERGY RATING; DESIGNED TO WORK AS A SYSTEM WITH THE VAILLANT UNISTORE 210L OR 300L UNVENTED HOT WATER CYLINDER; DAIKIN ALTHERMA 3 H HT — DAIKIN'S HIGH-TEMPERATURE HEAT PUMP RANGE (DELIVERS FLOW TEMPERATURES UP TO 70°C); PARTICULARLY RELEVANT FOR LONDON HOMES WHERE EXISTING RADIATORS CANNOT BE UPGRADED (E.G. LISTED BUILDINGS, FLATS WITH DISTRICT HEATING LEGACY CONSTRAINTS); THE HIGH-TEMPERATURE CAPABILITY (HT) ALLOWS THE ALTHERMA 3 HT TO WORK WITH EXISTING UNDERSIZED RADIATORS WITHOUT REPLACEMENT; AVAILABLE IN 4KW, 6KW AND 8KW; MITSUBISHI ECODAN — ONE OF THE ORIGINAL AND MOST ESTABLISHED ASHP BRANDS IN THE UK; THE MITSUBISHI ECODAN RANGE (MONOBLOC AND SPLIT SYSTEM) IS WIDELY INSTALLED IN LONDON SCHOOLS, HOSPITALS AND COMMERCIAL BUILDINGS AS WELL AS RESIDENTIAL; THE ECODAN 8.5KW R32 MONOBLOC IS A POPULAR CHOICE FOR LARGER LONDON HOMES; SAMSUNG EHS MONO HT QUIET — A QUIETER-OPERATION ASHP PARTICULARLY SUITABLE FOR DENSE LONDON TERRACE SITUATIONS WHERE NOISE (MCS 020 STANDARD COMPLIANCE) IS A PLANNING OR NEIGHBOUR CONSIDERATION.

THE BOILER UPGRADE SCHEME (BUS) IS THE UK GOVERNMENT GRANT FOR REPLACING FOSSIL FUEL BOILERS WITH HEAT PUMPS IN ENGLAND AND WALES. KEY BUS FACTS FOR LONDON HOMEOWNERS IN 2025: GRANT AMOUNT — £7,500 FOR AN AIR SOURCE HEAT PUMP (ASHP) INSTALLATION; £7,500 FOR A GROUND SOURCE HEAT PUMP (GSHP); ELIGIBILITY — OWNER-OCCUPIED PROPERTIES IN ENGLAND AND WALES; THE PROPERTY MUST HAVE A VALID EPC ISSUED IN THE LAST 10 YEARS WITH NO OUTSTANDING LOFT OR CAVITY WALL INSULATION RECOMMENDATIONS (OR A TECHNICAL REASON FOR EXEMPTION FROM THESE); THE INSTALLATION MUST BE BY AN MCS-REGISTERED INSTALLER; GRANT APPLICATION — THE MCS-REGISTERED INSTALLER APPLIES FOR THE BUS GRANT ON BEHALF OF THE LONDON HOMEOWNER; THE GRANT IS DEDUCTED FROM THE INSTALLATION INVOICE — THE LONDON HOMEOWNER PAYS THE NET AMOUNT AFTER GRANT; WHO APPLIES — ALWAYS THE MCS-REGISTERED INSTALLER (NOT THE HOMEOWNER); ENSURE YOUR LONDON INSTALLER IS CURRENT ON THE BUS APPROVED INSTALLER LIST; HEAT NETWORK EXEMPTION — LONDON PROPERTIES ON A HEAT NETWORK (DISTRICT HEATING) ARE NOT ELIGIBLE FOR THE BUS GRANT AS THEY CANNOT INSTALL AN INDIVIDUAL HEAT PUMP; MCS CERTIFICATION — ALL BUS-ELIGIBLE ASHP INSTALLATIONS MUST BE DESIGNED AND INSTALLED BY AN MCS (MICROGENERATION CERTIFICATION SCHEME) CERTIFIED INSTALLER AND TO MCS STANDARDS; THE MCS 020 HEAT PUMP PLANNING STANDARD APPLIES FOR NOISE AND PLANNING CONSIDERATIONS.

AIR SOURCE HEAT PUMP INSTALLATION COSTS IN LONDON IN 2025 (BEFORE BUS GRANT): TYPICAL 3-BED LONDON TERRACE (7KW VAILLANT AROTHERM PLUS, UNVENTED CYLINDER 210L, RADIATOR UPGRADES, CONTROLS) — £9,000-£15,000 BEFORE BUS GRANT; AFTER £7,500 BUS GRANT — £1,500-£7,500 NET COST; TYPICAL LARGER LONDON HOUSE (4-5 BED, 10KW VAILLANT OR DAIKIN, 300L CYLINDER, BUFFER VESSEL, RADIATOR UPGRADES) — £12,000-£20,000 BEFORE BUS GRANT; AFTER £7,500 BUS GRANT — £4,500-£12,500 NET COST; ASHP INSTALLATION ONLY (LIKE-FOR-LIKE, NO RADIATOR CHANGES, LONDON FLAT OR MODERN HOUSE WITH APPROPRIATE INSULATION, 5KW SYSTEM) — £5,000-£9,000 BEFORE BUS GRANT; AFTER £7,500 BUS GRANT — £0-£1,500 NET COST (SOME INSTALLATIONS BELOW GRANT AMOUNT); RADIATOR UPGRADES ONLY (SEPARATE LINE) — £1,000-£4,000 DEPENDING ON NUMBER OF RADIATORS IN LONDON PROPERTY; INSULATION IMPROVEMENTS (LOFT INSULATION, CAVITY WALL — SEPARATE FROM ASHP INSTALLATION) — LOFT INSULATION TYPICALLY £300-£600 FOR A LONDON TERRACE (OFTEN PARTLY FUNDED VIA ECO4 SCHEME); CAVITY WALL INSULATION APPROXIMATELY £600-£1,200 FOR A LONDON TERRACE. NOTE: LONDON ASHP INSTALLATION COSTS ARE TYPICALLY 10-25% HIGHER THAN THE UK AVERAGE DUE TO HIGHER LONDON LABOUR RATES, HIGHER LONDON MATERIAL HANDLING COSTS AND MORE COMPLEX LONDON ACCESS (TERRACE HOUSES WITH REAR GARDEN ACCESS ONLY VIA HOUSE OR SIDE GATE).