New building services
5.1 For each new fixed building service in a new or existing dwelling, the efficiency of the service should be no lower than the value set out in Section 6. If a proposed service is not covered in Section 6, the service should be shown to be no less efficient than a comparable service that is covered.
5.2 Both of the following apply to the efficiency claimed for a fixed building service.
a. The efficiency should be based on the appropriate test standard set out in Section 6.
b. The test data should be certified by a notified body.
5.3 For heating and hot water systems in new dwellings, paragraphs 5.8 to 5.19 should be followed, in addition to the system specific guidance in Section 6.
Replacement building services in existing dwellings
5.4 A replacement fixed building service should be at least as efficient as the value set out in Section 6 and should comply with either of the following.
a. Use the same fuel as the service being replaced and have an efficiency that is not worse than that of the service being replaced.
b. Use a different fuel than the service being replaced. The system should both:
i. not produce more CO2 emissions per kWh of heat than the appliance being replaced
ii. not have a higher primary energy demand per kWh of heat than the appliance being replaced.
Worked example
Replacing an old oil-fired boiler with emissions of 0.298kgCO2/kWh and primary energy of 1.180kWhPE/kWh at 85% efficiency with an LPG boiler with emissions of 0.241kgCO2/kWh and primary energy of 1.141kWhPE/kWh at 93% efficiency.
CO2 emissions
Oil-fired boiler: 0.298/0.85 = 0.35kgCO2/kWh
LPG boiler: 0.241/0.93 = 0.26kgCO2/kWh
Primary energy
Oil-fired boiler: 1.180/0.85= 1.39kWhPE/kWh
LPG boiler: 1.141/0.93 = 1.23kWhPE/kWh
The new LPG boiler has both lower CO2 emissions and primary energy than the oil-fired boiler being replaced, and therefore complies. It is also at least as efficient as the minimum efficiency as set out in Section 6 of this guidance.
NOTE: If the efficiency of the appliance being replaced is not known, the Standard Assessment Procedure, Tables 4a and 4b, should be used but with no adjustments from Tables 4c and 4d.
CO2 emission factors and primary energy factors should be taken from the Standard Assessment Procedure Table 12.
NOTE: Where a heat pump is installed which meets the minimum efficiency standards in this approved document, it should be deemed to be compliant with paragraph 5.4, without the need to carry out this calculation.
5.5 Where a replacement fixed building service involves a fuel-switch in a home with very low heat loss a higher primary energy for the new heating appliance may be acceptable. For example, replacing a gas boiler with direct electric heaters as part of a deep retrofit project, where the resulting heat loss of the dwelling is less than 25kWh/m2 per year.
5.6 If renewable technology such as a wind turbine or photovoltaic array is replaced, the new system should have an electrical output that is at least the same as that of the original installation.
5.7 Facilitating future connection to any local district heat networks should be considered (e.g. providing capped off connections in pipework to allow later connection to a local district heat network).
Sizing heating and hot water systems
Sizing space heating systems
5.8 The specification of space heating systems should be based on both of the following.
a. An appropriate heat loss calculation for the dwelling.
b. A sizing methodology that takes account of the properties of the dwelling, such as the Chartered Institute of Plumbing and Heating Engineering’s Plumbing Engineering Services Design Guide.
Systems should not be significantly oversized.
5.9 Where a gas combination boiler is used, the boiler type should be selected to modulate down to the typical heating load of the dwelling.
5.10 Where a wet heating system is either:
a. newly installed
b. fully replaced in an existing building, including the heating appliance, emitters and associated pipework all parts of the system including pipework and emitters should be sized to allow the space heating system to operate effectively and in a manner that meets the heating needs of the dwelling, at a maximum flow temperature of 55°C or lower.
Where it is not feasible to install a space heating system that can operate at this temperature (e.g. where there is insufficient space for larger radiators, or the existing distribution system is provided with higher temperature heat from a low carbon district heat network), the space heating system should be designed to the lowest design temperature possible that will still meet the heating needs of the dwelling.
NOTE: Low temperature requirements apply to space heating only. Further guidance can be found in the Building Research Establishment’s FB 59 Design of Low-temperature Domestic Heating Systems.
Sizing domestic hot water systems
5.11 Domestic hot water systems should be sized for the anticipated domestic hot water demand of the dwelling, based on BS EN 12831-3 or the Chartered Institute of Plumbing and Heating Engineering’s Plumbing Engineering Services Design Guide. Systems should not be significantly oversized.
NOTE: For temperature limits to control legionella bacteria in domestic hot water systems, see Approved Document G.
Sizing heat pump heating systems
5.12 Heat pumps should be selected to meet the full space heating requirement at the design condition chosen for heat loss calculations. This selection should account for the space heating flow temperature assumed in the heat emitter circuit(s), and not assume any heat will be supplied by additional electric heaters within the design external temperature range.
5.13 Reversible heat pump systems (i.e. those that provide both cooling and heating functions) should be designed such that they are optimised for heating.
Controls
System controls and zoning
5.14 For wet heating systems in new dwellings with a floor area of 150m2 or greater, a minimum of two independently controlled heating circuits should be provided.
5.15 System controls should be wired so that when there is no demand for space heating or hot water the heating appliance and pump are switched off.
5.16 Domestic hot water circuits that are supplied from a hot water store should have both of the following.
a. Time control that is independent of space heating circuits.
b. Electronic temperature control.
5.17 Primary hot water circuits for domestic hot water or heating should have fully pumped circulation where this is compatible with the heat generator.
5.18 Wet heating systems should ensure a minimum flow of water to avoid short-cycling.
5.19 For space heating systems, temperature control should be installed for the heating appliance.
Thermostatic room controls
5.20 For heating systems in new dwellings, or when a heat generator such as a boiler is replaced in an existing dwelling, each room should be provided with thermostatic room controls. These should be capable of being used to separately adapt the heating output in each room served by the heating appliance. Where justified in accordance with paragraph 5.21, heating may be controlled for each heating zone rather than individual rooms.
NOTE: There is no need to install thermostatic room controls in rooms/zones without heating in new or existing dwellings.
NOTE: Installing thermostatic room controls may not be technically feasible in some cases. These may include the following.
a. Dwellings with very low heat demand (e.g. less than 10W/m2).
b. Dwelling with buffer zones for heat absorption or dissipation with high thermal mass.
5.21 It may be justified to control a heating zone rather than individual rooms in either of the following cases.
a. In single-storey open-plan dwellings in which the living area is greater than 70% of the total floor area. In such cases, the dwelling should be considered as a single heating zone.
b. Where two adjacent rooms have a similar function and heating requirements (e.g. kitchen and utility room). In such cases, the adjacent rooms should be considered as a single heating zone.
NOTE: Exhaust air heat pump systems, which extract heat from the exhaust air of a dwelling, may not need to provide independent thermostatic control to individual rooms. Providing room/zone control on this type of system is unlikely to be economically and/or technically viable.
However, other space heating systems also in use in the same dwelling should be controlled using thermostatic room controls as described above.
NOTE: Commissioning heating systems is covered in Section 8.
5.22 The standards in paragraphs 5.20 and 5.21 may be satisfied by providing any of the following.
a. Both of the following.
i. A thermostat in a room that the heating circuit serves.
ii. An individual thermostatic room control for each heat emitter, such as a thermostatic radiator valve, on all heat emitters outside the room that contains the thermostat. Thermostatic radiator valves should not be used in the same room as the thermostat.
b. An individual room/heating zone thermostat or fan coil thermostat for each room or heating zone.
c. An individual networked heat emitter control for each emitter.
Controls in existing heating and domestic hot water systems
5.23 In addition to paragraphs 5.20 to 5.22, work on existing systems should incorporate the controls detailed in paragraphs 5.24 to 5.27.
5.24 If domestic hot water and space heating are controlled by a single time controller in the existing system, then these may continue to be controlled together after the work is complete. Otherwise, domestic hot water and space heating should each have separate time controls.
5.25 If work is carried out on a system that includes a boiler, a boiler interlock should be installed.
5.26 If replacing a hot water cylinder, the replacement cylinder should have an electronic temperature control, such as a cylinder thermostat.
5.27 If replacing a boiler, the boiler controls should meet the standards in Section 6 for the relevant wet heating system. (The boiler controls are considered to be part of the boiler installation.)
