Heating System Upgrades for London Victorian Terraces: Boiler, Heat Pump, and Controls

A MODERN CONDENSING GAS BOILER IS THE STANDARD HEATING SYSTEM UPGRADE FOR LONDON VICTORIAN TERRACES WHERE GAS SUPPLY IS AVAILABLE (MOST LONDON POSTCODES) AND WHERE AN AIR SOURCE HEAT PUMP IS NOT YET BEING CONSIDERED.

LEADING CONDENSING COMBI BOILER CHOICES FOR LONDON VICTORIAN TERRACES (2- TO 4-BEDROOM PROPERTIES): WORCESTER BOSCH GREENSTAR 8000 STYLE (24KW OR 28KW — THE MOST WIDELY INSTALLED COMBI BOILER IN LONDON RESIDENTIAL RENOVATION): EFFICIENCY: SEDBUK BAND A (91% NET SEASONAL EFFICIENCY). CONTROLS: COMPATIBLE WITH WORCESTER BOSCH WAVE SMART THERMOSTAT (TADO COMPETITOR) AND NEST. HOT WATER: 12 LITRES/MINUTE FLOW RATE AT 35°C RISE. GUARANTEE: 8-YEAR MANUFACTURER'S WARRANTY (WORCESTER ACCREDITED INSTALLER REQUIRED). VAILLANT ECOTEC PLUS 825 (25KW — THE SECOND MOST POPULAR LONDON COMBI BOILER): EFFICIENCY: SEDBUK BAND A (92% NET SEASONAL EFFICIENCY). ERPENERGY LABEL A. 5-YEAR STANDARD WARRANTY (10-YEAR WITH VAILLANT ADVANCE INSTALLER). IDEAL LOGIC MAX (25KW — THE BUDGET-CONSCIOUS CHOICE FOR LONDON RENTAL PROPERTY UPGRADES): EFFICIENCY: SEDBUK BAND A (91%). GUARANTEE: 7-YEAR MANUFACTURER'S WARRANTY. HOW TO SIZE A COMBI BOILER FOR A LONDON VICTORIAN TERRACE: A 3-BEDROOM LONDON VICTORIAN TERRACE (90-120 M² FLOOR AREA, SOLID WALLS, SOME DRAUGHT-PROOFING) TYPICALLY REQUIRES: 24KW TO 28KW COMBI BOILER (SINGLE BATHROOM — 1 SHOWER OR BATH AT A TIME). 30KW TO 35KW IF 2 BATHROOMS (SIMULTANEOUS HOT WATER DRAW RISK). A HEAT LOSS CALCULATION (BSRIA BG 12/2011 OR SAP CALCULATION) IS THE CORRECT BASIS FOR BOILER SIZING — NOT RULE-OF-THUMB GUESSES. OVER-SIZING A COMBI BOILER CAUSES "SHORT CYCLING" (FREQUENT ON/OFF CYCLING WITHOUT RUNNING LONG ENOUGH FOR EFFICIENT CONDENSING), WHICH REDUCES EFFICIENCY AND BOILER LIFE.

AIR SOURCE HEAT PUMPS (ASHP) ARE EMERGING AS AN ALTERNATIVE TO GAS BOILERS FOR LONDON VICTORIAN TERRACE HEATING — PARTICULARLY SINCE THE INTRODUCTION OF THE BOILER UPGRADE SCHEME (BUS) GRANT OF £7,500 FOR ASHP INSTALLATION IN ENGLAND.

HOW AN ASHP WORKS: AN ASHP EXTRACTS LATENT HEAT FROM THE OUTDOOR AIR (EVEN AT -15°C — MODERN ASHP OPERATE DOWN TO -25°C) AND USES A REFRIGERANT CYCLE TO AMPLIFY THIS HEAT FOR DELIVERY TO THE HEATING SYSTEM. THE EFFICIENCY OF AN ASHP IS EXPRESSED AS A COEFFICIENT OF PERFORMANCE (COP): A COP OF 3 MEANS 1 KWH OF ELECTRICITY PRODUCES 3 KWH OF HEAT. MODERN ASHP ACHIEVE SEASONAL COP (SCOP) OF 3 TO 4 UNDER UK CLIMATE CONDITIONS.

LEADING ASHP FOR LONDON VICTORIAN TERRACE RETROFIT: VAILLANT AROTHERM PLUS (7KW OR 10KW — THE MOST COMMONLY SPECIFIED ASHP FOR LONDON VICTORIAN TERRACE RETROFIT): MAXIMUM FLOW TEMPERATURE: 75°C — COMPATIBLE WITH EXISTING RADIATOR SYSTEMS AT HIGHER FLOW TEMPERATURES (IMPORTANT FOR VICTORIAN TERRACES WHERE THE RADIATOR SURFACE AREA MAY NOT BE SUFFICIENT FOR LOW-TEMPERATURE (45°C) OPERATION). SCOP: 4.2 AT A7/W35 (OUTDOOR AIR 7°C, WATER FLOW 35°C). DAIKIN ALTHERMA 3 H HT (HIGH-TEMPERATURE ASHP — FLOW TEMPERATURE TO 80°C): THE HIGH-TEMPERATURE CAPABILITY OF THE DAIKIN ALTHERMA 3 H HT (ALSO KNOWN AS THE DAIKIN ALTHERMA HT) MAKES IT WELL-SUITED TO LONDON VICTORIAN TERRACES WHERE REPLACING ALL RADIATORS IS NOT FEASIBLE — THE HIGH FLOW TEMPERATURE COMPENSATES FOR UNDERSIZED RADIATORS. SCOP: 3.9 AT A7/W55.

CHALLENGES OF ASHP IN LONDON VICTORIAN TERRACES: RADIATOR SIZING: STANDARD RADIATORS DESIGNED FOR 70-80°C FLOW TEMPERATURE (GAS BOILER SYSTEM) MAY PROVIDE INSUFFICIENT HEAT OUTPUT AT THE LOWER FLOW TEMPERATURES (35-55°C) OF A STANDARD ASHP. RADIATOR CAPACITY SHOULD BE CHECKED USING A HEAT LOSS CALCULATION AND UPGRADED WHERE REQUIRED — TYPICALLY, EXISTING SINGLE-PANEL RADIATORS SHOULD BE UPGRADED TO DOUBLE-PANEL DOUBLE-CONVECTOR (K2 OR K3) RADIATORS. HOT WATER: ASHP WITH A DEDICATED HOT WATER CYLINDER (200L TO 300L — MEGAFLO ECO UNVENTED OR GLEDHILL TORRENT SYSTEMMATE) IS REQUIRED. PLANNING: ASHP UNITS FALL UNDER PD (CLASS A GPDO 2015) IF: WITHIN THE SITE CURTILAGE, NOT WITHIN 1M OF A BOUNDARY, NOT IN A CONSERVATION AREA OR WORLD HERITAGE SITE, AND NOT ON A WALL OR ROOF FACING A HIGHWAY.

UPGRADING THE HEATING CONTROLS IN A LONDON VICTORIAN TERRACE FROM A SIMPLE PROGRAMMABLE TIMER AND SINGLE THERMOSTAT TO A SMART, ZONED HEATING CONTROL SYSTEM IS ONE OF THE MOST COST-EFFECTIVE ENERGY EFFICIENCY IMPROVEMENTS AVAILABLE — TYPICALLY COSTING £300 TO £900 AND REDUCING HEATING BILLS BY 10 TO 25%.

TADO SMART THERMOSTAT AND EXTENSION KIT: TADO V3+ WIRED SMART THERMOSTAT: REPLACES THE EXISTING ROOM THERMOSTAT — WIFI-CONNECTED, GEOFENCING (HEATING TURNS ON WHEN YOU ARE APPROACHING HOME, OFF WHEN YOU LEAVE), OPEN WINDOW DETECTION (HEATING PAUSES WHEN RAPID TEMPERATURE DROP INDICATES OPEN WINDOW). TADO RADIATOR THERMOSTAT V3+ (SMART TRV — REPLACES EXISTING MANUAL TRRVS): INDIVIDUALLY CONTROLS EACH RADIATOR, ALLOWS ROOM-BY-ROOM TEMPERATURE SCHEDULES — E.G. BEDROOM RADIATOR TURNS ON AT 6:30AM TO WARM THE ROOM BEFORE WAKING. THE TADO STARTER KIT (SMART THERMOSTAT + 3 SMART TRVs): APPROXIMATELY £200 TO £300 SUPPLY — SELF-INSTALL OR PROFESSIONAL INSTALL.

HEATMISER NEOSTAT V2 (THE PREFERRED CHOICE FOR LONDON HIGH-SPECIFICATION RENOVATION PROJECTS WITH MULTIPLE HEATING ZONES): HEATMISER NEOSTAT (TOUCHSCREEN THERMOSTAT — AVAILABLE IN BLACK OR WHITE, 4-INCH DISPLAY) WITH HEATMISER NEO HUB: ALLOWS UP TO 8 ZONES (8 NEOSTAT THERMOSTATS — ONE PER ROOM) CONTROLLED FROM A SINGLE NEOHUB — SUITABLE FOR LARGER LONDON VICTORIAN TERRACES WITH MULTIPLE HEATING ZONES (GROUND FLOOR UFH ZONE + UPSTAIRS RADIATOR ZONE + LOFT ZONE). COMPATIBLE WITH MOST COMBINATION AND SYSTEM BOILERS AND WITH MULTIPLE UFH MANIFOLD ACTUATORS.

THERMOSTATIC RADIATOR VALVES (TRVS — THE MINIMUM UPGRADE FOR ALL LONDON VICTORIAN TERRACES): BS EN 215 TRV (DRAYTON ULTRAD PLUS OR PEGLER PERFORMA TRV): ALL RADIATORS EXCEPT THE BATHROOM AND THE ROOM WITH THE MAIN THERMOSTAT SHOULD HAVE TRVs. PART L (CURRENT) REQUIRES TRVs ON ALL NEW OR REPLACEMENT RADIATORS. THE EXISTING MANUAL LOCK-SHIELD RADIATOR VALVES ON OLDER LONDON TERRACE HEATING SYSTEMS SHOULD BE REPLACED WITH TRVs AS PART OF A HEATING UPGRADE.

A HEATING SYSTEM UPGRADE IN A LONDON VICTORIAN TERRACE IS OFTEN INCOMPLETE WITHOUT REVIEWING AND POTENTIALLY REPLACING THE EXISTING RADIATORS — PARTICULARLY WHERE AN ASHP IS BEING INSTALLED (WHICH REQUIRES RADIATORS SIZED FOR LOWER FLOW TEMPERATURES) OR WHERE THE EXISTING RADIATORS ARE ORIGINAL CAST-IRON COLUMN RADIATORS (BEAUTIFUL, PERIOD-CORRECT, AND HIGH-MASS — BUT SLOW TO HEAT UP AND COOL DOWN).

CALCULATING RADIATOR SIZE FOR A LONDON VICTORIAN TERRACE ROOM: THE HEAT OUTPUT REQUIRED FROM EACH RADIATOR IS DETERMINED BY THE HEAT LOSS OF THE ROOM: HEAT LOSS = FABRIC HEAT LOSS (U-VALUE X AREA X TEMPERATURE DIFFERENCE FOR EACH ELEMENT — WINDOWS, WALLS, FLOORS, CEILING) + VENTILATION HEAT LOSS (AIR CHANGE RATE X VOLUME X TEMPERATURE DIFFERENCE). FOR A TYPICAL UNINSULATED LONDON VICTORIAN TERRACE FRONT BEDROOM (12 M², SOLID WALLS, SINGLE-GLAZED BAY WINDOW, SUSPENDED TIMBER FLOOR): APPROXIMATE HEAT LOSS: 750W TO 1,200W AT -3°C DESIGN TEMPERATURE (THE BSRIA -3°C OUTDOOR DESIGN TEMPERATURE FOR LONDON). A STANDARD SINGLE-PANEL RADIATOR (TYPE 11 — 600MM HIGH X 1000MM WIDE) OUTPUTS: AT 70°C MEAN WATER TEMPERATURE: APPROXIMATELY 900W — ADEQUATE FOR GAS BOILER. AT 50°C MEAN WATER TEMPERATURE (ASHP AT 55°C FLOW): APPROXIMATELY 550W — UNDERSIZED, WOULD NEED REPLACEMENT WITH K2 DOUBLE-PANEL DOUBLE-CONVECTOR OR LARGER SINGLE PANEL.

SYSTEM REBALANCING AFTER BOILER OR RADIATOR CHANGES: AFTER ANY CHANGE TO A LONDON TERRACE HEATING SYSTEM (BOILER REPLACEMENT, RADIATOR ADDITION, TRV INSTALLATION), THE SYSTEM MUST BE REBALANCED: LOCK-SHIELD VALVES ON EACH RADIATOR ARE ADJUSTED TO SET THE CORRECT FLOW RATE THROUGH EACH RADIATOR. COMMISSIONING INVOLVES MEASURING FLOW AND RETURN TEMPERATURES AT EACH RADIATOR AND ADJUSTING THE LOCK-SHIELD VALVE UNTIL THE TEMPERATURE DIFFERENCE (ΔT) ACROSS EACH RADIATOR IS APPROXIMATELY 10-12°C (FOR A STANDARD HIGH-TEMPERATURE GAS SYSTEM) OR 5-8°C (FOR AN ASHP SYSTEM).

LONDON HOMEOWNERS UPGRADING FROM GAS BOILERS TO LOW-CARBON HEATING SYSTEMS MAY QUALIFY FOR GOVERNMENT FINANCIAL INCENTIVES — THE MOST SIGNIFICANT CURRENTLY BEING THE BOILER UPGRADE SCHEME (BUS).

BOILER UPGRADE SCHEME (BUS) — ENGLAND: INTRODUCED APRIL 2022, EXTENDED TO 2028. GRANT OF £7,500 FOR ASHP INSTALLATION (AIR SOURCE HEAT PUMP — REPLACING AN EXISTING FOSSIL FUEL HEATING SYSTEM WITH AN ASHP). ELIGIBILITY: OWNER-OCCUPIED PROPERTY IN ENGLAND WITH A VALID EPC (LODGED IN THE LAST 10 YEARS — CHECK AT GOV.UK/FIND-ENERGY-CERTIFICATE). LOFT AND CAVITY WALL INSULATION MUST BE INSTALLED (WHERE TECHNICALLY FEASIBLE AND COST-EFFECTIVE) BEFORE THE GRANT CAN BE CLAIMED — FOR A SOLID-WALL LONDON VICTORIAN TERRACE, THIS MEANS EWI OR IWI MAY NEED TO BE SPECIFIED OR EXEMPTED. THE GRANT IS CLAIMED BY THE REGISTERED INSTALLER (MICROGENERATION CERTIFICATION SCHEME — MCS CERTIFIED INSTALLER) — THE HOMEOWNER RECEIVES THE DISCOUNT FROM THE INSTALLER AT THE POINT OF INSTALLATION. ECO4 SCHEME: FOR HOUSEHOLDS IN FUEL POVERTY (OWNER-OCCUPIERS AND PRIVATE TENANTS ON QUALIFYING BENEFITS WITH EPC D OR BELOW) — COVERS BOILER REPLACEMENT, INSULATION, AND FIRST-TIME CENTRAL HEATING. APPLIED THROUGH ENERGY SUPPLIERS — GOV.UK/ECO4. HOME UPGRADE GRANT (HUG2): FOR OWNER-OCCUPIERS IN ENGLAND WITH EPC E, F, OR G AND ANNUAL HOUSEHOLD INCOME BELOW £36,000 — GRANTS TOWARD ENERGY EFFICIENCY MEASURES INCLUDING HEATING SYSTEMS.

HEATING SYSTEM UPGRADE COSTS IN LONDON VARY BY THE SCOPE OF WORK AND THE SYSTEM CHOSEN.

COMBI BOILER REPLACEMENT (WORCESTER BOSCH GREENSTAR 8000 STYLE 25KW — SUPPLY AND FIT INCLUDING GAS SAFE REGISTRATION AND PART L COMPLIANCE CERTIFICATE): SUPPLY (BOILER ONLY): £900 TO £1,600. INSTALLATION (LABOUR + SYSTEM FLUSH + INHIBITOR + GAS SAFE): £600 TO £1,200. TOTAL COMBI BOILER REPLACEMENT (LIKE-FOR-LIKE POSITION): £1,500 TO £2,800. BOILER RELOCATION (DIFFERENT ROOM OR POSITION): ADD £500 TO £2,500 FOR PIPEWORK ALTERATIONS, NEW FLUE, GAS PIPE EXTENSION.

AIR SOURCE HEAT PUMP (VAILLANT AROTHERM PLUS 7KW — SUPPLY AND INSTALL INCLUDING HOT WATER CYLINDER, SYSTEM CHANGES, MCS COMMISSIONING): SUPPLY (ASHP OUTDOOR UNIT + INDOOR UNIT + 200L CYLINDER): £5,000 TO £9,000. INSTALLATION (PIPEWORK, CONTROLS, COMMISSIONING): £2,000 TO £5,000. RADIATOR UPGRADES (IF REQUIRED — TYPICALLY 3 TO 6 RADIATORS IN A 3-BED TERRACE): £200 TO £400 PER RADIATOR SUPPLY AND FIT. TOTAL ASHP SYSTEM (BEFORE BUS GRANT): £9,000 TO £18,000. AFTER £7,500 BUS GRANT: £1,500 TO £10,500 NET COST.

SMART THERMOSTAT UPGRADE (TADO STARTER KIT — SELF-INSTALL): £200 TO £300 SUPPLY. HEATMISER NEOSTAT WITH NEOHUB (4-ZONE — PROFESSIONALLY INSTALLED): £600 TO £1,200 SUPPLY AND INSTALL.

TRV UPGRADE (ALL RADIATORS — DRAYTON ULTRAD PLUS, SUPPLY AND FIT — PER RADIATOR): £50 TO £90 PER RADIATOR SUPPLY AND FIT.