Electric Underfloor Heating: Mat vs Cable, Thermostats & Running Costs

Quick Answer: Electric underfloor heating uses resistance cable beneath the floor to produce radiant heat. Heating mats (cable pre-spaced on a mesh) are easiest to install in regular-shaped rooms; loose cable is better for irregular areas. A dual-input thermostat with air and floor sensors is required. Running costs are approximately 8-12p/kWh × watts/m² — typically a bathroom costs 1-3p per hour to run.

Summary

Electric underfloor heating (eUFH) is particularly popular in bathrooms and kitchens where it provides comfortable background heat and warm floors without visible radiators. It's typically used as a primary heat source in well-insulated spaces or as a supplementary comfort heater in rooms that already have wet central heating.

Unlike hydronic (wet) underfloor heating — which requires a heat source, pump, and manifold — electric UFH is a direct conversion of electricity to heat through resistance cable. It's significantly cheaper to install than wet UFH (no pipework, manifold, or pump) but more expensive to run, especially if used as a primary heat source in larger rooms.

The regulatory requirements for electric UFH overlap between electrical installation (BS 7671:2018+A2:2022) and thermal performance. The installation is notifiable work under Part P. A floor temperature-limiting sensor must be used with certain floor coverings (particularly wood and laminate) to prevent damage to the floor.

Key Facts

Quick Reference Table

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Area Type Recommended Output Suitable For Notes
Bathroom (primary heat) 150-200 W/m² All bathrooms Standard; run by programmable thermostat
Kitchen (supplementary) 100-150 W/m² Tiled or stone floors Supplementary to radiator
Living room (supplementary) 100 W/m² Various floor types Check floor type temperature limit
Conservatory (primary) 150-200 W/m² Well-insulated conservatory Poor insulation makes this expensive
Bathroom wet room 150 W/m² All floors IP-rated thermostat required if in wet zone
Floor Covering Max Floor Temperature Notes
Ceramic/porcelain tiles 40°C Most compatible; no restrictions
Natural stone 40°C Ensure no thermal shock risk for sealed stone
Laminate 27°C Floor sensor limiting essential; check manufacturer
Engineered hardwood 27°C Floor sensor limiting essential; check floor warranty
Solid hardwood Not recommended Risk of cracking; some manufacturers prohibit
Carpet Not recommended Very poor heat transfer; not practical
Vinyl/LVT 27°C Check specific product; some LVT not suitable

Detailed Guidance

Mat vs Loose Cable: When to Use Each

Heating mats:

Loose cable:

Calculation for loose cable:

Thermostat Selection and Wiring

A dual-function thermostat with air sensor and floor sensor is standard for electric UFH:

Air sensor: Measures room temperature; controls comfort level (e.g., target air temperature of 21°C)

Floor sensor: A separate NTC thermistor probe laid in the screed or tile adhesive between heating cables; prevents floor exceeding the maximum temperature for the floor covering

Thermostat wiring (typical):

Thermostat position: Outside of the Zone 2 IP boundary in bathrooms (see bathroom zones); typically on the wall adjacent to the bathroom door, not inside the bathroom zone.

IP rating in bathrooms: If the thermostat must be inside Zone 2, it requires IP44 or better. Consider installing it in an adjacent landing or hallway where possible.

Installation Step by Step

Preparation:

  1. Check the subfloor is clean, level, and dry
  2. Fit any insulation board (strongly recommended; reduces heat loss to subfloor by 50%+)
  3. Install a plastic conduit for the thermostat floor probe — run to the sensor location between cables; leave an adequate loop so the probe can be withdrawn for replacement if needed

Mat/cable installation: 4. Unroll the mat or lay loose cable starting from the thermostat position 5. Avoid cutting or crossing cables; mats can be turned by cutting the carrier mesh (NOT the cable) 6. Maintain minimum 50mm spacing between cable passes 7. Keep cables at least 50mm from walls 8. Position the thermostat probe conduit between two cable runs; the probe tip should be midway between cables

Testing: 9. Use a multimeter to check cable resistance before and after installation; compare against manufacturer specification (should be within ±10%) 10. Use a 500V insulation resistance tester to check cable insulation to earth (should be >1MΩ; most good cable reads >100MΩ) 11. Record resistance values in the commissioning certificate

Floor covering: 12. Apply tile adhesive or screed over the cable (depth per manufacturer instructions — typically 15-20mm in adhesive) 13. Allow full cure before connecting the circuit and running the system

Running Cost Calculation

Running cost per hour = (watts ÷ 1000) × electricity tariff (p/kWh)

Example — 5m² bathroom, 150W/m², 30p/kWh tariff:

For larger areas used as primary heat sources, running costs escalate significantly. A 20m² living room at 150W/m² running 8 hours daily would cost approximately £2-3 per day — heating the living room with electric UFH alone is expensive at standard electricity tariffs.

Making it cheaper:

Frequently Asked Questions

Do I need a new circuit for electric underfloor heating?

For anything more than a very small mat (under 1kW), yes — a dedicated circuit from the consumer unit is strongly recommended. This provides clean fault isolation, ensures correct circuit protection sizing, and is generally required for the warranty. For a typical bathroom mat (500-750W), a 16A circuit with 30mA RCBO is standard.

Can electric underfloor heating be fitted under laminate or engineered wood?

Yes, but carefully. A floor temperature sensor limiting thermostat is essential — the floor must not exceed 27°C (or the floor manufacturer's specified maximum, whichever is lower). Some wood floor manufacturers void their warranty if UFH is installed without their specific approval; check the floor warranty before installation. Never install under solid hardwood (too high expansion/contraction risk).

What's the minimum installation depth for a heating mat?

The cable should be fully embedded in adhesive or screed — typically 15-20mm above the cable. Insufficient depth can create hot spots (damaging the cable), poor heat distribution, and cracked tiles. Most manufacturers specify a minimum of 10mm of adhesive or mortar coverage above the cable.

Can I lay tiles over electric UFH straight away?

No. Tile adhesive and any levelling compound must be fully cured before the heating system is switched on. This typically means at least 7-28 days depending on the screed or adhesive type. Switching on too early while the screed is green can cause cracking. After the cure period, bring the temperature up gradually over 3-7 days to the full operating temperature.

Regulations & Standards