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

L1(b), L2 O N L I N E V E R S I O N Table 6.2 M inimum heat generator seasonal efficiency for boiler systems in existing buildings(1)(2) Fuel type System Boiler seasonal efficiency (gross calorific value) Natural gas Single-boiler ≤400kW output 91% Single-boiler 401kW–2MW output 88% Single-boiler >2MW output 84% Multiple-boiler 84% for any individual boiler 91% for overall multi-boiler system LPG Single-boiler ≤2MW output 93% Single-boiler >2MW output 88% Multiple-boiler 88% for any individual boiler 93% for overall multi-boiler system Oil Single-boiler 93% Multiple-boiler 88% for any individual boiler 93% for overall multi-boiler system NOTES: 1. Seasonal efficiencies should be calculated in line with paragraphs 6.3 to 6.6. 2. Non-condensing boilers should be fitted with a flue condensing kit where feasible and where the boiler is likely to be able to operate in condensing mode (e.g. variable temperature circuits). Single-boiler systems and multiple-boiler systems with identical boilers 6.3 The seasonal efficiency of the boiler should be determined using equation 6.1. boiler seasonal efficiency = 0.81η + 0.19η equation 6.1 30% 100% Where: η is the gross boiler efficiency measured at 30% load 30% η is the gross boiler efficiency measured at 100% load. 100% NOTE: Efficiencies based on net calorific value should be converted to efficiencies based on gross calorific value, using the appropriate conversion factor in the Standard Assessment Procedure version 10 Table E4. Equation 6.1 assumes that the efficiency at 15% load is the same as that at 30% load. 6.4 Equation 6.1 applies to both of the following. a. Single-boiler systems that: i. produce low temperature hot water ii. have an output of less than or equal to 400kW. b. Multiple-boiler systems that: i. produce low temperature hot water ii. comprise individual boilers with identical efficiencies iii. have an output of less than or equal to 400kW. 40 Approved Document L Volume 2, 2021 edition Building Regulations 2010 O N L I N E V E R S I O N