Underfloor Heating in London Homes: Types, Costs and When to Install It

**Wet (hydronic) underfloor heating:** A network of plastic pipes (typically PEX or MLCP) embedded in a screed or within a low-profile panel system. Hot water circulates through the pipes from a manifold connected to your boiler or heat pump.

• Advantages:
• •Running cost is lower than electric UFH over the long term (especially with a heat pump)
• •Compatible with a gas boiler (at higher flow temperatures) or an ASHP (at lower flow temperatures — typically 35–45°C)
• •Well-suited to large areas — the pipe network is cost-effective over a large floor plate
• •Slower to heat up (typically 30–60 minutes from cold) but excellent for continuous use or zones that are kept at a constant background temperature

• Disadvantages:
• •Higher installation cost (screed depth, manifold plumbing, zone control)
• •Requires coordination with the floor build-up (screed depth adds 70–100mm to the floor level — significant in a Victorian property where door heights are fixed)
• •Not easily retro-fitted to existing floors without significant disruption
• •Requires proper zone control and thermostats

**Electric (resistive) underfloor heating:** Electric heating mats or cables laid under tiles, stone, or LVT (Luxury Vinyl Tile) in a thin adhesive bed. Independently powered from a dedicated circuit.

• Advantages:
• •Low installation cost
• •Very thin (3–4mm) — no significant change to floor level
• •Can be retro-fitted under a hard floor covering with minimal disruption
• •Fast heat-up (10–20 minutes) — ideal for bathrooms and kitchens used intermittently
• •Independent zones easily controlled by individual thermostats

• Disadvantages:
• •Higher running cost than wet UFH — electricity costs significantly more than gas per kWh
• •Not appropriate as the primary heating system in a large room (the running cost is too high)
• •Most appropriate for supplementary heating in bathrooms and en-suites, under tiled floors

• **The practical conclusion for most London projects:**
• •**Bathroom and en-suite**: electric UFH is the right choice — cheap to install, fast to respond, appropriate for the small areas involved
• •**Extension ground floor (kitchen-diner, sitting room)**: wet UFH as part of the extension screed is the best choice — particularly where an ASHP is installed or planned
• •**Existing rooms being refurbished**: electric UFH under new tile or stone if the disruption of a screed is not appropriate; wet UFH only if the floor is being completely renewed

**The best time to install wet UFH is during an extension build or a full ground floor refurbishment.** Installing wet UFH after the floor screed has been poured requires breaking out the screed, laying the pipes, and re-screeding. This is expensive and disruptive. In a new extension, the UFH pipes are laid before the screed is poured — the additional cost over standard screed is relatively modest.

• **Good opportunities for wet UFH installation:**
• •During a rear extension or wraparound extension (the extension screed receives UFH pipes before pouring)
• •During a full ground floor refurbishment where existing floors are being removed (suspended timber ground floors being replaced with a new beam-and-block or concrete screed)
• •During a basement conversion (new concrete floor in the basement can accommodate a wet UFH system)

• **Good opportunities for electric UFH:**
• •During any bathroom or kitchen tile installation (the mats lay under the tile adhesive bed — no floor level disruption)
• •As a retro-fit supplement in any room where hard flooring is being replaced

• **When to wait:**
• •Do not specify wet UFH in an extension and then immediately ask the contractor to route from the existing boiler through existing floor voids — this may require significant additional work. Plan the pipe route from the manifold to the boiler (or ASHP) as part of the design before construction.
• •Do not install electric UFH under flooring that is not compatible (carpet, engineered wood over an uninsulated subfloor, floating floors with thick underlays — all reduce efficiency and can void the heater warranty).

• **Floor screed depth with wet UFH:**
• Wet UFH pipes embedded in screed require a minimum screed depth of 65–75mm over the insulation layer. On a ground floor extension with a concrete sub-base:
• •150mm sub-base
• •50mm PIR insulation (floor insulation)
• •Polythene DPM
• •75mm screed with UFH pipes
• •Total floor build-up (from sub-base top to screed surface): approximately 125mm

This must be planned against the finished floor level required at the junction with the existing house floor (typically the two must be at the same level or with a defined step). In a Victorian terrace with a raised ground floor (typical in older London properties), this is usually achievable.

• **Wet underfloor heating (new extension or full ground floor refurbishment):**
• •Supply and installation of UFH pipes, manifold, and zone controls in a new extension screed: £3,500–£7,000 for a standard 20–30m² extension
• •Larger ground floor (40–60m²): £5,500–£10,000
• •Additional cost of 75mm liquid screed over standard 50mm screed: included in above or approximately £15–£25/m² additional
• •Manifold with zone controls and thermostats: £600–£1,500 depending on number of zones
• •Connecting to existing boiler or new ASHP: additional plumbing — allow £500–£1,500

• **Electric underfloor heating (bathroom, kitchen retro-fit under tiles):**
• •Electric UFH mat (200W/m², thermostatic control), supply and installation: £60–£100/m² (mat, thermostat, electrical connection)
• •Typical bathroom (4m²): £350–£600 supply and installation
• •Kitchen floor (15m²): £1,000–£1,800

• **Common mistakes to avoid:**
• •Installing wet UFH under timber flooring without specifying UFH-compatible engineered wood (standard engineered wood with thick plywood base does not transmit heat effectively — specify a thin-veneer product rated for UFH with a thermal resistance of under 0.10 m²K/W)
• •Over-sizing the system — UFH in a well-insulated extension will run at lower temperatures than in a poorly insulated space, and the zones should be designed for the actual heat load
• •Not including a room thermostat — UFH without individual room thermostats wastes energy and reduces comfort