Conservation of fuel and power: Approved Document L, Volume 2 — Buildings other than dwellings

O N L I N E V E R S I O N L1(b), L2 Table 6.5 Minimum thermal efficiencies for domestic hot water (DHW) systems DHW system Fuel type Heat generator seasonal Product standard type efficiency (gross calorific value) Direct-fired: Natural gas 91%(1) BS EN 15502-2 or new and LPG 92%(1) BS EN 89 or existing buildings BS EN 26 as appropriate Indirect- Natural gas 91% (boiler efficiency) Use equations (as appropriate) in paragraphs 6.3 to 6.6. fired: new If primary return temperature ≤55°C, use equation LPG 91% (boiler efficiency) and existing 6.1 (0.81η + 0.19η ) to calculate boiler seasonal buildings 30% 100% Oil 91% (boiler efficiency) efficiency. If primary return temperature >55°C, use boiler full load efficiency (1.0η at 80/60°C flow/return 100%) temperatures. If boiler seasonal efficiency values are obtained as net values, the factors in SAP 10 Table E4 should be used to convert them to gross values. Electrically- 100% assumed heated: new and existing buildings NOTE: 1. In exceptional circumstances, where a condensing boiler cannot feasibly be fitted in an existing building (for example, where there is insufficient space for a replacement flue system), a boiler with the following minimum seasonal efficiency may be used: a. 80% for natural gas b. 79% for LPG. 6.25 Where efficiency data is not readily available, efficiencies should be calculated using manufacturers’ recovery rates and equations 6.5 and 6.6. gross thermal efficiency = heater output / gross input equation 6.5 recovery rate specific heat heater temperature rise = of heater in × capacity of × equation 6.6 output of water litres/second water 45 Building Regulations 2010 Approved Document L Volume 2, 2021 edition O N L I N E V E R S I O N