Wet UFH wiring
Wet UFH heated by central plant (gas boiler, ASHP, GSHP) — water at 35–45°C flow temperature distributed through PEX or PERT pipework laid in screed or floor build-up. Manifold (Polypipe, Wundatherm, Uponor): brass or stainless distribution with one flow + return loop per zone; flow meters; mixing valve modulating boiler/ASHP higher flow to UFH lower temperature. Wiring centre (Heatmiser, Salus, Honeywell): receives demand from room thermostats; opens 2-port valve actuators (5–10W each — usually 230V mains, some 24V) to permit flow to each zone; signals boiler/ASHP via volt-free contact to fire; controls UFH pump if separate from boiler primary. Electrical install: 230V supply from CU (typically 6A or 10A circuit) to wiring centre; manifold sited in plant room or utility; pipework first-fix before screed; commissioning after screed cured (28+ days). Cost £450–£1,800 per zone supplied + installed (includes thermostat, actuator, wiring centre share, valve + pipework). Smart control: Heatmiser NeoHub (most popular UK), Honeywell evohome, Tado UFH — replaces basic wiring centre + thermostats with app-controlled multi-zone system; £450–£1,200 add. Boiler/ASHP interlock: prevents short-cycling — only fires when UFH demand from at least one zone.
Electric UFH wiring
Electric UFH = heating mat or loose cable directly embedded in tile adhesive or screed; resistance heating at 150–200W/m² typical bathroom + kitchen; 100W/m² in carpeted bedroom (lower output, primary heat from radiator). Mat or cable supplied with cold tail (3m thermostat-to-mat unheated cable) + factory-fitted thermal sensor; floor-mounted thermostat with sensor probe in screed close to heating element + air temperature sensor in thermostat. Mat brands: Warmup DSCM (mesh), Devi DEVIheat, Heatmat WHM200, ProWarm Touch. Electrical install: dedicated radial 2.5mm² T+E from CU (typically 16A RCBO; check mat wattage × area = total current); 30mA RCD mandatory (RCBO preferred); thermostat IP rating — IP44 minimum in bathroom Zone 2 (or remote sensor + thermostat outside bathroom). Cost £350–£750 install per room (mat + thermostat + dedicated circuit). Bathroom 12V SELV preferred (no shock risk in wet area): Warmup DCM-PRO Low Voltage, Heatmiser SelvCare — premium £150–£385 cost; 12V transformer requires plant location outside bathroom + Class II install. Cool zones: not effective sole heating for cold London winter — supplement with towel rail or low-output radiator.
Specification + practical
Wet UFH preferred where central plant exists (boiler/ASHP) + retrofit floor build-up feasible (50–80mm screed + 25mm insulation + UFH = 75–105mm depth — issue in retrofit where ceiling height constrained). Electric UFH preferred where: no central heat source nearby, room-specific local heating, fast warm-up wanted (tile cold to touch problem), bathroom with thin screed budget (tile + 6mm hardibacker + mat — 10mm only). Cost comparison: wet UFH £85–£185/m² supplied + installed (whole-floor); electric UFH £85–£185/m² supplied + installed (similar but cheaper plant). Running cost: wet UFH at 35°C flow + ASHP COP 3.5 = ~£0.10/kWh heat; electric UFH = £0.30/kWh direct electric = 3× more expensive. Use electric for periodic comfort (bathroom morning 30min); wet for whole-house primary heating. Smart control (Heatmiser NeoHub + sensor per room): predictive heating — learns user pattern + occupancy + thermal lag → optimises run schedule. 20–35% energy savings per Salus + Heatmiser case studies. Specify at design stage; retrofit Smart NeoHub possible if wiring centre + room thermostats already installed.
