What This Requirement Covers
Approved Document L sets minimum efficiency standards for heating systems in new and existing buildings. When a heating system is installed or replaced, it must meet these minimum standards. The requirements have progressively increased over time, driving the transition from non-condensing to condensing boilers and, more recently, towards heat pumps.
Key Requirements
Gas and Oil Boilers
- New installations: All gas and oil boilers must be condensing boilers
- Minimum seasonal efficiency: 92% ErP (for gas boilers) and 93% ErP (for oil boilers)
- ErP (Energy related Products) efficiency is the European standard for measuring boiler efficiency
- The boiler must be sized to match the heat demand of the building (oversizing wastes energy)
- Heating controls must include: programmer/timer, room thermostat, and thermostatic radiator valves (TRVs) on all radiators except the reference radiator
Heat Pumps
- Minimum Seasonal Coefficient of Performance (SCOP): 2.5 for space heating
- Heat pump performance is heavily influenced by the design flow temperature; lower flow temperatures give higher efficiency
- The system must be designed for low flow temperatures (35-45 degrees C) with appropriately sized heat emitters (radiators or underfloor heating)
Heating Controls
The minimum heating control package for a wet central heating system includes
- A time control (programmer or timer) to set heating on/off times
- A room thermostat (or programmable room thermostat) to control temperature
- Thermostatic radiator valves (TRVs) on all radiators (except in the room with the room thermostat)
- A boiler interlock to prevent the boiler firing when no heat is required
- Weather compensation or load compensation controls are recommended and improve SAP performance
Commissioning
- All heating systems must be commissioned by a competent person
- Commissioning includes: setting the boiler flow temperature, balancing the radiator circuit, setting TRV heads, programming the controls, and recording all settings
- A commissioning certificate must be provided to the building owner and Building Control
Practical Compliance Tips
- Always replace like-for-like with a condensing boiler; it is illegal to install a non-condensing boiler as a replacement
- Size the boiler correctly using a heat loss calculation (not just matching the existing boiler size, which may be oversized)
- When installing a heat pump, design the radiator and pipework system for the lower flow temperatures; retrofitting underperforming radiators is expensive
- Fit weather compensation controls where the boiler supports them; this improves efficiency by 3-5%
- Ensure the commissioning is completed and recorded; incomplete commissioning is a common reason for Building Control holding back the completion certificate
- Register the boiler installation with the manufacturer for warranty purposes and with Gas Safe (for gas boilers) or OFTEC (for oil boilers)
- Provide the building owner with the boiler manual, commissioning record, and operating instructions