Underfloor Heating in London: Types, Costs and What Works in Period Properties

There are two fundamentally different types of underfloor heating system: Wet (hydronic) UFH: pipes embedded in a screed or laid on a mat in a low-profile system, carrying hot water from the boiler or heat pump. This is the most efficient system for large areas and whole-house installation. Wet UFH runs at lower flow temperatures (typically 35-45°C) than radiators, which makes it very compatible with heat pumps and modern condensing boilers running at lower temperatures. Suited to: extensions (where a new screed can be laid); ground floors (where floor depth is available); and whole-house installations. Electric UFH: electrical heating mats or cables laid directly under floor tiles or floating floor finishes. Faster and cheaper to install than wet UFH, but more expensive to run (electricity is approximately 3-4x the cost of gas per kWh, and 5-8x the cost of a heat pump). Best suited to: bathrooms and kitchens (small areas where installation simplicity and running cost are balanced); supplementary heating in rooms already served by the boiler system; and projects where a new screed is not practical. For an extension project in London where a new concrete slab or screed is being laid, wet UFH is almost always the better long-term choice. For a bathroom renovation without floor-up access, electric UFH is the practical option.

Wet UFH requires the pipes to be embedded in either: a traditional wet screed (pipes laid on insulation, covered by 65-80mm of sand-cement or anhydrite screed) — the most reliable system and the industry standard for extensions and ground floors; or a low-profile overlay system (aluminium spreader plates and thin pipes fitted on top of the existing floor, with a self-levelling compound or thin overlay board) — adds only 15-20mm to the floor height, making it suitable for renovation projects where floor height is critical. Floor build-up for a traditional wet screed UFH system (from bottom up): existing floor / ground: sub-base compacted; insulation board (minimum 75mm PIR) below the screed — essential to direct the heat upward into the room rather than downward into the ground; polythene sheeting (vapour barrier); UFH pipe loops fixed to the insulation; 65-75mm sand-cement or anhydrite screed; floor finish (tiles, engineered wood, LVT). Total additional depth above existing floor level: approximately 150-160mm for a new extension slab with insulation. For a renovation overlay on an existing floor: 15-20mm (overlay system only). The insulation below the screed is critical — without it, the heat goes into the ground rather than the room and the system is inefficient. The screed must be allowed to cure properly before the floor finish is laid (typically 28 days for sand-cement; 10-14 days for anhydrite). Heating and cooling cycles during curing are needed to minimise screed cracking.

Installing UFH in a Victorian London terraced house (as opposed to a new extension) presents specific challenges: Suspended timber ground floors: most Victorian London terraces have suspended timber ground floors over a sub-floor void. Installing UFH under a suspended timber floor requires a different approach from a solid concrete floor — either: lifting the floorboards and fitting UFH panels between or below the joists (suitable for low-output electric UFH or specialist low-temperature wet UFH panels designed for timber joist floors); or removing the existing floor, excavating, and installing a new concrete slab with wet UFH in screed. The latter is a major structural and disruptive project. Floor finish compatibility with UFH: some floor finishes work better over UFH than others. Ceramic and porcelain tiles: excellent — high thermal conductivity, fast response, compatible with all UFH systems. Stone tiles: excellent thermal conductivity, but ensure the stone is not frost-sensitive and that joints accommodate thermal movement. Engineered hardwood: compatible with UFH if specified for this use and laid as a floating floor (not glued) — solid hardwood is less compatible due to greater thermal movement. LVT (Luxury Vinyl Tile): compatible with UFH if specified for this use. Carpet: possible but significantly reduces UFH efficiency — use low-tog rated carpet and underlay. Standard domestic carpet and underlay can add an insulation effect that severely reduces the heat output of the UFH system.

Wet UFH costs in London (new extension or screed): UFH pipes and manifold supply: approximately £25-£50/m2 for the pipe loops and manifold. Screed supply and installation (including insulation below): approximately £45-£80/m2. Controls (thermostats, actuators, programmer): £400-£1,200 for a standard single-zone or multi-zone controls package. Professional installation (running pipes, connecting manifold, commissioning): typically included within the overall extension or floor installation package, but as a standalone: £20-£40/m2. Typical total wet UFH cost (pipes, screed, insulation, controls, installation) for a 25m2 extension floor: £4,000-£8,000. Electric UFH costs in London (bathroom or kitchen): electric mat supply (per m2): £30-£80/m2 for standard mats; £50-£100/m2 for dual-layer or higher output mats. Programmable thermostat and controls: £80-£200. Installation of a 4m2 bathroom floor with electric UFH mat and thermostat: £600-£1,200 supply and install. Running costs for electric UFH in a 4m2 bathroom (running 1-2 hours per day at 150W/m2 at 25p/kWh): approximately £55-£110 per year — cost-effective for small areas.

A well-designed UFH system requires a heat loss calculation to confirm the required output — simply laying UFH pipes without calculation can result in an under-performing system if the floor area, insulation specification, flow temperature, and pipe spacing are not coordinated. Key design inputs: room heat loss (determined by the insulation of walls, floor, roof, and window area and specification); desired floor temperature (maximum 29°C for occupied areas, 35°C for bathrooms without prolonged bare-foot contact, 33°C for large open areas); pipe spacing (200mm centres is standard; 150mm for higher-output areas); flow temperature (typically 35-45°C for UFH — this determines boiler and heat pump compatibility). Zoning: a well-designed system has separate zones for different areas (ground floor open plan, bathrooms, bedrooms if applicable) with individual thermostats per zone. This allows flexibility in heating schedule and temperature. A whole-house wet UFH system on a heat pump requires the highest level of design rigour — the heat pump's efficiency (COP) is highly sensitive to flow temperature, and undersizing the pipe loops or floor area will force the heat pump to run at higher temperatures, reducing efficiency.