Air Source Heat Pumps for London Homes: Complete Guide to Costs, Performance, and Installation

AN AIR SOURCE HEAT PUMP (ASHP) EXTRACTS HEAT ENERGY FROM OUTDOOR AIR AND MOVES IT INTO THE HOME — MUCH LIKE A REFRIGERATOR IN REVERSE. THE REFRIGERANT CYCLE ALLOWS THE UNIT TO DELIVER 2.5-4 UNITS OF HEAT ENERGY FOR EVERY 1 UNIT OF ELECTRICAL ENERGY CONSUMED. THIS RATIO IS KNOWN AS THE COEFFICIENT OF PERFORMANCE (COP) OR, ACROSS A FULL SEASON, THE SEASONAL COEFFICIENT OF PERFORMANCE (SCOP).

KEY EFFICIENCY METRICS: - SCOP: THE AVERAGE EFFICIENCY OVER THE WHOLE HEATING SEASON — A HIGHER NUMBER MEANS MORE HEAT PER KWH OF ELECTRICITY. CURRENT MCS-CERTIFIED MODELS ACHIEVE SCOP 3.0-4.5 IN UK CONDITIONS. - COP AT DESIGN CONDITIONS: THE EFFICIENCY AT THE DESIGN HEATING TEMPERATURE (TYPICALLY -7°C OUTDOOR, 55°C FLOW IN UK). BEST-IN-CLASS UNITS ACHIEVE COP 2.0-2.5 AT THIS CONDITION. - A35/W35 RATING: THE STANDARD TEST CONDITION FOR ASHP EFFICIENCY — MEASURED AT 35°C OUTDOOR AIR TEMPERATURE, 35°C WATER FLOW TEMPERATURE. THIS IS A MILD-WEATHER EFFICIENCY AND IS SIGNIFICANTLY HIGHER THAN REAL-WORLD COLD-WEATHER PERFORMANCE.

WHY LOWER FLOW TEMPERATURE MATTERS: THE EFFICIENCY OF A HEAT PUMP DECREASES AS THE DIFFERENCE BETWEEN OUTDOOR AIR TEMPERATURE AND HEATING WATER FLOW TEMPERATURE INCREASES. A SYSTEM RUNNING AT 35°C FLOW IS SIGNIFICANTLY MORE EFFICIENT THAN ONE RUNNING AT 55°C FLOW. THIS IS WHY: - UNDERFLOOR HEATING (TYPICALLY 35-45°C FLOW) IS THE IDEAL EMITTER FOR HEAT PUMPS - LARGE-FORMAT LOW-TEMPERATURE RADIATORS (MYSON FINESSE LOW TEMPERATURE, ULTRAHEAT KANAL, STELRAD VITA, PURMO COMPACT P TYPE 22 OR 33 AT LOWER DELTA T) ARE NEEDED WHERE UNDERFLOOR HEATING IS NOT POSSIBLE - EXISTING STANDARD-OUTPUT RADIATORS IN A VICTORIAN TERRACE MAY BE UNDERSIZED FOR HEAT PUMP FLOW TEMPERATURES — RADIATOR UPGRADES ARE OFTEN REQUIRED

LONDON CLIMATE CONTEXT: LONDON (WEATHER STATION: HEATHROW) HAS A DESIGN TEMPERATURE OF -3°C (AS PER BS EN 12831). THIS IS MILDER THAN MOST OF THE UK, WHICH MEANS LONDON HOMES ARE AMONG THE BEST LOCATIONS FOR HEAT PUMP PERFORMANCE IN THE COUNTRY. SCOP FIGURES FOR LONDON ARE TYPICALLY 5-10% HIGHER THAN MANUFACTURERS\' UK AVERAGE RATINGS.

THE FOLLOWING MODELS REPRESENT THE LEADING OPTIONS FOR LONDON RESIDENTIAL INSTALLATIONS IN THE 5-12KW RANGE (APPROPRIATE FOR MOST 3-5 BEDROOM PROPERTIES):

VAILLANT AROTHERM PLUS: - RANGE: 5KW, 7KW, 10KW, 15KW (MONOBLOC — ALL REFRIGERANT COMPONENTS EXTERNAL) - SCOP A7/W35: UP TO 5.1 (7KW MODEL) - COP AT A-7/W55 (DESIGN CONDITION): 2.0 - NOISE LEVEL (1M FROM UNIT): 53-55 DBA (7KW) - MINIMUM OUTDOOR TEMPERATURE: -15°C - HOT WATER CYLINDER: UNISTORE AIR CYLINDER 200L OR 250L RECOMMENDED - STRENGTHS: VERY HIGH SEASONAL EFFICIENCY; COMPETITIVE NOISE LEVELS; WELL-REGARDED UK SERVICE NETWORK - MCS CERTIFIED: YES

DAIKIN ALTHERMA 3 H HT: - RANGE: 4KW, 6KW, 8KW, 12KW, 16KW (SPLIT SYSTEM — INDOOR HYDRO BOX + EXTERNAL UNIT) - SCOP A7/W35: UP TO 5.08 (8KW MODEL) - COP AT A-7/W55: 1.97 (8KW) - NOISE LEVEL: 53-54 DBA (8KW) - MINIMUM OUTDOOR TEMPERATURE: -20°C - HOT WATER: INTEGRATED HOT WATER CYLINDER OPTION (180L OR 230L IN HYDRO BOX) OR EXTERNAL CYLINDER - STRENGTHS: HIGH-TEMPERATURE (HT) VARIANT CAN DELIVER 65°C FLOW — USEFUL FOR EXISTING SYSTEMS WITH CONVENTIONAL RADIATORS; DAIKIN UK SERVICE NETWORK - MCS CERTIFIED: YES

SAMSUNG EHS MONO R290: - RANGE: 5KW, 8KW, 12KW, 16KW - REFRIGERANT: R290 (PROPANE) — GLOBAL WARMING POTENTIAL (GWP) 3 VS R410A (GWP 2088); FUTURE-PROOF REFRIGERANT - SCOP A7/W35: UP TO 4.87 - STRENGTHS: LOWEST GWP REFRIGERANT IN CLASS; COMPETITIVE PRICING - MCS CERTIFIED: YES

MITSUBISHI ELECTRIC ECODAN PUHZ-SW: - RANGE: 5KW, 8.5KW, 11.2KW, 14KW, 16KW - SCOP A7/W35: UP TO 4.50 - STRENGTHS: VERY ESTABLISHED UK MARKET PRESENCE; STRONG SERVICE NETWORK; QUIET OPERATION (TWIN-ROTARY COMPRESSOR) - MCS CERTIFIED: YES

SIZING GUIDANCE FOR LONDON HOMES: - 2-BED VICTORIAN FLAT (80M²): 5-6KW - 3-BED MID-TERRACE VICTORIAN (90-120M²): 7-8KW - 4-BED SEMI-DETACHED (130-160M²): 8-10KW - 5-BED DETACHED (160-220M²): 10-14KW CORRECT SIZING REQUIRES A HEAT LOSS CALCULATION (BS EN 12831) — DO NOT GUESS. OVERSIZING CAUSES EXCESSIVE CYCLING AND REDUCED EFFICIENCY.

THE BOILER UPGRADE SCHEME (BUS) — ADMINISTERED BY OFGEM — PROVIDES A GRANT OF £7,500 TOWARDS THE INSTALLATION OF AN AIR SOURCE HEAT PUMP (FROM APRIL 2024 ONWARDS).

ELIGIBILITY CRITERIA: 1. THE PROPERTY MUST BE IN ENGLAND OR WALES. 2. THE PROPERTY MUST HAVE A VALID EPC (ENERGY PERFORMANCE CERTIFICATE) WITH NO OUTSTANDING RECOMMENDATIONS FOR LOFT INSULATION OR CAVITY WALL INSULATION. (IF THE EPC HAS SUCH RECOMMENDATIONS, THE INSULATION MUST BE INSTALLED FIRST — OR AN UPDATED EPC OBTAINED SHOWING THE MEASURES ARE NOT APPLICABLE TO THE PROPERTY TYPE). 3. THE INSTALLATION MUST BE CARRIED OUT BY AN MCS-CERTIFIED HEAT PUMP INSTALLER. 4. THE PROPERTY MUST NOT HAVE RECEIVED A PREVIOUS HEAT PUMP GRANT UNDER THE RENEWABLE HEAT INCENTIVE (RHI) OR BUS. 5. THE GRANT APPLIES TO OWNER-OCCUPIED AND PRIVATE RENTED PROPERTIES (NOT SOCIAL HOUSING).

HOW THE GRANT WORKS: THE INSTALLER CLAIMS THE GRANT ON THE HOMEOWNER\'S BEHALF — THE HOMEOWNER SIMPLY PAYS THE INSTALLER THE NET AMOUNT AFTER DEDUCTING THE £7,500 GRANT. THERE IS NO COMPLEX APPLICATION PROCESS FOR THE HOMEOWNER.

EPC REQUIREMENTS IN MORE DETAIL: IF THE EPC RECOMMENDS LOFT INSULATION (AND THE PROPERTY HAS A LOFT) OR CAVITY WALL INSULATION (AND THE PROPERTY HAS UNFILLED CAVITY WALLS), THESE MUST BE ADDRESSED BEFORE THE BUS GRANT CAN BE CLAIMED. FOR LONDON VICTORIAN SOLID-WALL TERRACES (WHICH DO NOT HAVE CAVITY WALLS), THIS REQUIREMENT OFTEN DOES NOT APPLY — SOLID WALLS ARE NOT SUITABLE FOR STANDARD CAVITY WALL INSULATION AND THE EPC SHOULD REFLECT THIS.

IMPORTANT NOTE: GRANTS AND SCHEME CONDITIONS ARE SUBJECT TO CHANGE — ALWAYS CONFIRM CURRENT BUS CRITERIA WITH AN MCS-CERTIFIED INSTALLER OR AT OFGEM\'S WEBSITE BEFORE PLANNING YOUR PROJECT.

AN ASHP INSTALLATION IN A LONDON HOME INVOLVES MORE THAN SIMPLY SWAPPING OUT THE BOILER. THE FOLLOWING ELEMENTS MUST ALL BE ADDRESSED:

EXTERNAL UNIT SITING: THE EXTERNAL UNIT (COMPRESSOR/FAN ASSEMBLY) MUST BE POSITIONED ON EXTERNAL WALL, GROUND, OR FLAT ROOF WITH: ADEQUATE AIRFLOW (MINIMUM CLEARANCES: TYPICALLY 300MM REAR, 300MM SIDES, 1M FRONT CLEAR OF OBSTACLES); SOLID ANTI-VIBRATION BASE (RUBBER ANTI-VIBRATION MOUNTS OR CONCRETE PAD); ACCESS FOR MAINTENANCE (600MM WORKING SPACE). FOR LONDON TERRACES WITH SMALL REAR GARDENS, WALL-MOUNTING ON BRACKETS IS POSSIBLE (SPECIALIST BRACKETS, E.G., HILTI OR LIEBIG ANCHOR FIXINGS TO MASONRY).

PLANNING PERMISSION: ASHPS IN ENGLAND ARE PERMITTED DEVELOPMENT (NO PLANNING PERMISSION REQUIRED) PROVIDED: VOLUME IS LESS THAN 0.6M³; ONE UNIT PER PROPERTY; NOT WITHIN 1M OF THE PROPERTY\'S BOUNDARY; NOT ON A WALL OR ROOF FACING A HIGHWAY; NOT IN A CONSERVATION AREA OR ON A LISTED BUILDING. CONSERVATION AREA PROPERTIES IN LONDON REQUIRE PLANNING PERMISSION FOR EXTERNAL UNITS. CHECK WITH YOUR LOCAL PLANNING AUTHORITY IF UNCERTAIN.

HOT WATER CYLINDER: ASHPs TYPICALLY CANNOT REPLACE A COMBI BOILER WITHOUT THE ADDITION OF A HOT WATER CYLINDER — THE HEAT PUMP CANNOT DELIVER DOMESTIC HOT WATER (DHW) ON DEMAND AT SUFFICIENT FLOW RATE. A WELL-INSULATED UNVENTED CYLINDER (180-300L) IS REQUIRED: RECOMMENDED OPTIONS INCLUDE VAILLANT UNISTORE AIR 200L; DAIKIN INTERNAL HYDRO BOX INTEGRATED CYLINDER; GLEDHILL STAINLESS LITE PLUS 210L; ALBION ULTRACYL 250L.

RADIATOR COMPATIBILITY AND UPGRADES: HEAT PUMP INSTALLER SHOULD ASSESS EXISTING RADIATORS AGAINST A FLOW TEMPERATURE OF 45-50°C. WHERE RADIATORS ARE UNDERSIZED AT THAT FLOW TEMPERATURE, UPGRADES TO LARGER PANELS (STELRAD COMPACT K2 DOUBLE PANEL, PURMO COMPACT P33, OR THERMASKIRT SKIRTING HEATER) ARE NEEDED. UNDERFLOOR HEATING IN NEW EXTENSIONS IS IDEAL — SPECIFY 35-40°C FLOW FOR MAXIMUM HEAT PUMP EFFICIENCY.

ELECTRICAL SUPPLY: ASHPs REQUIRE A DEDICATED CIRCUIT FROM THE CONSUMER UNIT — TYPICALLY 32A OR 40A SINGLE PHASE FOR 7-12KW UNITS. CONFIRM WITH AN ELECTRICIAN THAT EXISTING CONSUMER UNIT HAS CAPACITY AND THAT SUPPLY CABLE IS ADEQUATE.

INSTALLATION TIMELINE: TYPICALLY 2-4 DAYS FOR AN MCS-CERTIFIED INSTALLER.

COSTS (LONDON MARKET, 2025-2026): - 7-8KW ASHP (VAILLANT AROTHERM PLUS OR DAIKIN ALTHERMA), 200-210L CYLINDER, INSTALLATION: £10,000-16,000 GROSS - AFTER £7,500 BUS GRANT: £2,500-8,500 NET - RADIATOR UPGRADES (IF NEEDED): £1,000-5,000 DEPENDING ON NUMBER AND SIZE - ELECTRICAL UPGRADES: £300-1,000 - TOTAL NET COST RANGE: £4,000-14,000 AFTER GRANT