Wet UFH — the default for whole-floor heating
Wet UFH circulates warm water (35–45°C flow) through PEX or PERT pipes laid at 150–200mm centres in a heated screed or floor build-up. Cost £75–£140/m² supplied and installed, varying by build-up type: screeded (50–75mm sand-cement or liquid anhydrite) £95–£140/m² heavy thermal mass slow response; low-profile (Wunda LowPro 18mm) £75–£110/m² faster response, suitable for retrofit; suspended-floor spreader plates (between joists) £55–£95/m² for first-floor or timber-floor retrofits no screed. Working perfectly with heat pumps at 35–40°C flow (matches heat pump optimum); also compatible with gas boilers at 45–55°C flow. Single manifold (£280–£450) controls multiple zones (typically one manifold per floor; zones per room with actuators £45–£85 per zone). Lifespan 50+ years for pipe (PEX rated 50 years at 60°C); manifold and pump 15–20 years. Best for: ground-floor extensions, open-plan refurbishments, whole-floor rooms above 15m², homes with heat pump heating, homes with timber-floor underspecification (UFH plates compensate).
Electric UFH — small zones only
Electric UFH uses heating cable or pre-mat (loose cable at 80–150W/m² or pre-spaced mat at 150–200W/m²) embedded in 8–12mm tile adhesive layer beneath floor finish. Install cost £45–£85/m² (mat £35–£55/m² + thermostat £85–£180 + tiling labour adder £10–£20/m²). Heat-up time: 20–40 minutes (vs wet UFH 2–4 hours) — responsive for occasional use. Crucial cost factor: running cost. Electricity at 28p/kWh × 150W/m² × 4 hours/day × 30 days = £15/m²/month — i.e. running a 8m² bathroom electric UFH all day in winter costs £100–£140/month. Wet UFH from a heat pump costs £4–£6/m²/month. Therefore: electric UFH viable only for bathrooms (intermittent use, small area) and small ensuites (4–8m²). Never specify electric UFH for whole-room living areas — the running cost is prohibitive and EPC penalises electric heating. Combine: electric UFH in master bathroom and ensuite; wet UFH elsewhere. Lifespan: 25–30 years (cable failure unrepairable without lifting floor).
Build-up, screed and floor finish compatibility
Wet UFH screeded build-up: 100mm insulation (PIR 0.022 W/mK) + 80mm PE membrane + pipe at 150mm centres clipped to PE board + 65mm screed (sand-cement, 28-day cure) or 50mm liquid anhydrite (Gypsol, 7-day cure). Total build-up 195–230mm from substrate to finished floor. Liquid anhydrite faster install and self-levelling but requires careful drying before tiling. Wet UFH low-profile (Wunda, Polypipe Overlay) 18–22mm thick — sits directly on existing floor with no screed; finished floor goes straight on top. Floor finish compatibility: stone and ceramic tile excellent (high thermal conductivity); engineered timber 14–22mm acceptable; carpet must be low tog (<2.5 tog total carpet + underlay otherwise it insulates heat in floor); solid timber not recommended (moisture cycling). Always check floor finish manufacturer UFH compatibility before specifying. Output: wet UFH delivers 70–100 W/m² at 40°C flow with 18°C room — sufficient for well-insulated extensions; for older fabric or full retrofit needs higher flow temperatures and tighter pipe centres.
Retrofit and zoning strategy
Whole-house wet UFH retrofit cost £8,500–£18,000 depending on build-up (low-profile saves screed but adds pipework labour). Practical sequence: lift existing floor, install insulation + UFH + screed (or low-profile if floor height critical) — typical 8–14 day disruption per zone. Mix-and-match strategy: wet UFH ground floor + radiators upstairs is common — first floor screed buildup creates head-height issues, and bedroom heat demand is lower. Zoning: split house into 4–8 zones with individual thermostats so unused rooms run cooler; cost £350–£650 per additional zone but pays back in operating cost over 8–12 years. Smart controls (Heatmiser Neostat, Honeywell evohome, Nest UFH-compatible) £140–£280 per thermostat. Commissioning is critical — UFH installer must balance manifold loops to design flow rate; un-commissioned UFH typically delivers 30–50% of design output.
