Heating Systems for London Renovations: Boilers, Heat Pumps and Underfloor Heating

Gas boilers remain legal to install in existing properties in 2026 — the previously proposed 2025 ban on new gas boiler installations in existing homes was not implemented, and the government's current policy permits gas boiler replacements in existing homes beyond 2035 for properties where a heat pump is not suitable.

• **When a new gas boiler makes sense:**
• •The existing property has an adequate gas supply and is connected to the mains gas network
• •The heating system is well-maintained and effective but the boiler is at end of life
• •The property's heat loss is too high for a heat pump to operate efficiently without significant fabric improvement (i.e., the property needs a higher flow temperature than a heat pump is efficient at)
• •Budget constraints make the capital cost of a heat pump (£8,000–£18,000 installed) prohibitive vs. a gas boiler replacement (£2,500–£4,500 installed)

• **New gas boiler specification:**
• •Condensing combi boiler (most common for London homes) or system boiler with unvented cylinder for larger households with higher hot water demand
• •New gas boiler must be ErP A-rated (condensing specification)
• •Boiler size should be specified by a heating engineer based on property heat loss calculation — oversizing is common and reduces efficiency

**Gas boiler future policy:** The government's current trajectory is to phase out new gas boiler installations in new-build properties (already in effect via the Future Homes Standard from 2025) and to introduce policy from 2035 encouraging existing property owners to switch to heat pumps when their boiler reaches end of life. The mechanism (subsidy, obligation, or ban) remains subject to policy development.

Air source heat pumps (ASHPs) extract heat from outside air and concentrate it to provide space heating and hot water. They are the primary low-carbon heating technology for UK homes and the focus of current government policy.

**The Boiler Upgrade Scheme (BUS) grant:** £7,500 government grant available for a qualifying ASHP installation in England and Wales (2026 figure — confirm current amount when applying). Grant is paid directly to the MCS-accredited installer and deducted from the installation cost.

• **Installed cost with grant:**
• A typical ASHP installation for a London 3-bed terrace:
• •Without grant: £10,000–£18,000 installed (depending on system complexity, hot water cylinder, pipework upgrades, and radiator upgrades)
• •With BUS grant (£7,500): £2,500–£10,500 net cost

• **When a heat pump works well:**
• •Property has adequate loft and/or wall insulation — heat pumps operate at lower flow temperatures (typically 35–55°C) than gas boilers (typically 65–75°C), so the heating system must distribute heat through larger-area radiators or underfloor heating to achieve the same room temperature
• •Adequate external space for the outdoor unit (typically 1.0m × 0.4m footprint) — standard planning rules permit heat pumps in England subject to siting requirements
• •Property has three-phase electricity supply or adequate single-phase capacity (most residential properties have sufficient capacity)

• **When a heat pump is less suitable:**
• •Poor fabric (uninsulated solid walls, single glazing) — installing a heat pump before improving the fabric wastes the investment
• •Very high hot water demand (large household, bath-heavy usage) — heat pumps take longer to heat water than gas boilers
• •Listed buildings or Conservation Areas where the outdoor unit position may be restricted

**Heat pump and renovation:** A major renovation is the ideal time to install underfloor heating (which is highly compatible with the low flow temperatures of heat pumps) and to improve the building fabric — making these decisions together rather than sequentially produces the most efficient and lowest-cost outcome.

Underfloor heating (UFH) is the preferred distribution system for heat pumps and also a desirable amenity in kitchens, bathrooms, and open-plan spaces regardless of the heat source.

**Two types of UFH:**

• **Wet UFH (water-fed):**
• •Pipes laid in the floor screed, fed from the boiler or heat pump
• •Most efficient when laid in screed (floor acts as a thermal store)
• •Higher installation cost (pipe, manifold, screed, additional floor height of 70–100mm)
• •Running costs lower than electric UFH
• •Best suited to extensions, new screed floors, and ground floor areas where floor level can accommodate the build-up
• •Cost: typically £80–£150/m² for supply and install in a renovation context

• **Electric UFH (mat or cable):**
• •Heating element or mat laid under floor finish (typically tile or stone)
• •No screed required — minimal floor height addition (2–5mm for mat type)
• •Easy to install in bathrooms and kitchen areas being retiled
• •Higher running costs than wet UFH
• •Not suitable as the primary space heating system for most rooms — used for comfort in bathrooms and kitchens
• •Cost: typically £40–£90/m² for supply and install

• **UFH and floor finishes:**
• Not all floor finishes are suitable for use over UFH:
• •**Suitable:** porcelain and ceramic tile, stone, LVT/SPC (check manufacturer specification), resin
• •**Suitable with care:** engineered hardwood (check manufacturer specification — solid hardwood is generally not suitable over wet UFH)
• •**Unsuitable:** solid hardwood, standard carpet (high thermal resistance blocks the heat)

**Zoning:** Wet UFH systems are designed with manifolds that zone the heating — typically one zone per room or area, allowing independent temperature control. This is specified at first-fix stage and should be designed as part of the heating system rather than added afterwards.