What This Requirement Covers
Underfloor heating (UFH) is an increasingly popular heating system in new UK dwellings, particularly when combined with heat pumps. UFH operates at lower flow temperatures than radiators, making it highly compatible with the low-carbon heating systems required by the 2021 Part L and the Future Homes Standard.
Key Requirements
Types of Underfloor Heating
- Wet (hydronic) systems: Hot water circulates through pipes embedded in or below the floor finish. Compatible with heat pumps, boilers, and renewable heat sources.
- Electric systems: Heating cables or mats embedded in or below the floor finish. Higher running costs but simpler to install. Suitable for small areas or retrofit situations.
Energy Efficiency Benefits
- UFH operates at flow temperatures of 35-45 degrees C (compared to 55-80 degrees C for radiators)
- Lower flow temperatures significantly improve heat pump efficiency (SCOP increases by approximately 0.5 for every 10 degrees C reduction in flow temperature)
- UFH heats the room from the floor up, providing even heat distribution and perceived warmth at lower air temperatures
- In SAP calculations, UFH with a heat pump achieves a significantly better DER than radiators with a heat pump
Design Requirements
- Floor construction must accommodate the heating pipes or cables and achieve the Part L U-value requirement
- Insulation below the UFH: Essential to prevent heat loss downwards; minimum 50 mm rigid insulation (PIR or EPS) above the structural floor
- Screed thickness: Typically 65-75 mm over the heating pipes for wet systems
- Floor coverings: The floor covering must be suitable for use with UFH; carpet and underlay should have a combined thermal resistance not exceeding 1.5 tog
- Each room must have an individual room thermostat or thermostatic valve for temperature control
Practical Compliance Tips
- Design UFH for low flow temperatures from the outset, especially when combining with a heat pump
- Insulate below the UFH to minimise downward heat loss; this is critical for ground-floor and first-floor applications
- Use individual room thermostats to prevent overheating and to meet Part L heating control requirements
- Choose floor coverings carefully; thick carpet and underlay reduce the effectiveness of UFH
- For retrofit installations, consider low-profile UFH systems (18-25 mm build-up) to minimise floor level changes
- Commission the UFH system and balance the flow rates to each zone for even heat distribution
- Provide the homeowner with clear instructions on how to programme and control the system