Underfloor Heating: Choosing Between Wet and Electric Systems
Underfloor heating (UFH) delivers heat through the floor surface rather than wall-mounted radiators, producing a more even temperature distribution and freeing up wall space. The key decision is whether to install a wet system (hot water pipes embedded in the floor) or an electric system (resistance heating cables or mats). The right choice depends on project type, budget, and heat source.
Wet Underfloor Heating Systems
Wet UFH circulates warm water through a network of plastic or MLCP pipes embedded in the floor structure. A manifold distributes flow to each circuit, with zone controls and a mixing valve to regulate flow temperature.
Advantages:
- Substantially lower running costs than electric, especially with a heat pump
- Suitable for whole-house heating as a replacement for radiators
- Low flow temperature (35–45°C) makes it the ideal partner for air source or ground source heat pumps
- Long lifespan — properly installed pipework can last 50+ years
Disadvantages:
- Higher installation cost (pipework, manifold, screed or low-profile system)
- Requires significant floor build-up (typically 65–100mm for a screeded system)
- Slower response time than radiators — zone thermostats and weather compensation controls are important
- Should be installed by a qualified plumber or heating engineer
Where wet UFH is appropriate:
- New build projects where the floor build-up can be planned from the outset
- Ground floor extensions where a new screed or low-profile system can be laid
- Whole-house renovation projects where floors are being lifted anyway
Electric Underfloor Heating Systems
Electric UFH uses resistance heating cables (loose cables or factory-assembled mats) installed beneath the floor finish. The cables heat up when current passes through them, warming the floor surface from below.
Advantages:
- Low installation cost — mats can be self-installed in a single room in a day
- Minimal floor build-up (as little as 3–4mm for a heating mat under adhesive tile)
- Fast response time compared to wet systems
- Suitable for retrofit and single-room applications
Disadvantages:
- High running costs — electricity is approximately 3–4x the cost per kWh of gas
- Not practical as a whole-house heating solution
- Relies on good floor insulation to avoid heat loss downward
Where electric UFH is appropriate:
- Single-room retrofit (bathroom, kitchen) where the floor is already being replaced
- Rooms where wet pipework is impractical (e.g., above a structural concrete slab with no access below)
- Supplementary heating to boost comfort in a specific room
Key brands for electric systems include Warmup, Devi (Danfoss), and Nu-Heat.
Floor Build-Up Requirements
This is often the deciding factor in the wet vs electric decision for retrofit projects.
Wet screeded system: Pipes are embedded in a sand/cement screed or proprietary flowing screed. Total floor build-up is typically 65–100mm above the subfloor insulation. This is only practical where floor levels can be raised (extensions, ground-up new build) or where the existing floor is being fully removed.
Wet low-profile system: Panel-and-plate systems (aluminium spreader plates in routed chipboard or pre-formed panels) can reduce the build-up to 15–22mm. Response time is faster than screed. Suitable for timber subfloor situations.
Electric mat: Under ceramic or porcelain tile, a heating mat adds as little as 3–4mm to the adhesive bed — effectively nothing. Under a floating floor, a self-levelling compound is applied over the cable (typically 15–25mm total).
Good insulation beneath the system is essential for both types. Without it, heat is lost downward rather than into the room above.
Heat Loss Calculation
Before specifying UFH output, a heat loss calculation for each room is required. UFH output is typically 60–120 W/m² depending on flow temperature, pipe spacing, and floor finish. If the room’s heat loss exceeds what the floor area can deliver, supplementary heating is needed. This calculation should be carried out at design stage by the installer.
Compatibility with Heat Pumps
Wet UFH is an excellent match for air source and ground source heat pumps. Heat pumps operate most efficiently at low flow temperatures, and UFH requires exactly that — typically 35–45°C, compared to 60–80°C for radiators. A property with wet UFH throughout, fed by a heat pump, can achieve Coefficient of Performance (CoP) figures significantly higher than the same heat pump running radiators.
When specifying UFH for a heat pump installation, ensure the system is designed for low-temperature operation throughout, including the manifold, mixing valves, and zone controls.
Thermostats and Zone Control
Each room or zone should have its own thermostat. Smart thermostats with scheduling and app control significantly improve running cost efficiency for both wet and electric systems. For wet systems with multiple zones, a wiring centre and zone valves (or a manifold-mounted actuator system) are required.
For simple single-room electric systems, a dedicated UFH thermostat with a floor sensor is standard — it controls both the floor surface temperature and room air temperature.
Installation
Wet UFH should be installed by a qualified plumber or heating engineer familiar with UFH design. The system must be pressure-tested before screeding. Commissioning includes balancing flow rates across circuits and setting the mixing valve correctly.
Electric systems in bathrooms must be installed in compliance with BS 7671 Part P requirements, and the circuit must be RCD-protected. Heating mats and cables carry BEAB/CE approvals and come with clear installation instructions.
Running Cost Comparison
As a rough guide for a typical 20m² room in an average UK property: an electric system might cost £1.50–£2.50 per day to run as the primary heat source in winter. A wet system connected to a heat pump might cost £0.30–£0.60 per day for the equivalent output. Over a heating season, the difference is substantial, which is why electric is typically recommended only for single rooms or supplementary use.
Key brands for wet systems include Warmup, Wunda, Rehau, and Polypipe.
