Section G3 Hot water supply and systems

  1. The Requirement G3
    1. Performance
      1. General
        1. Provision of hot water supply
          1. Design and installation of directly or indirectly heated hot water storage systems
            1. General
              1. Vented hot water storage systems
                1. Unvented hot water storage systems – all systems
                  1. Unvented hot water storage systems – systems up to 500 litres capacity and 45kW power input
                    1. Unvented hot water storage systems – systems over 500 litres capacity or over 45kW power input
                    2. Safety devices
                      1. Non-self-resetting energy cut-outs
                        1. Temperature and pressure relief devices
                          1. Electric water heating
                          2. Solar water heating
                            1. Discharge pipes from safety devices
                              1. Discharge pipe D1
                                1. Tundish
                                  1. Discharge pipe D2
                                    1. Termination of discharge pipe
                                    2. Prevention of excessive temperatures
                                      1. Prevention of scalding
                                        1. Installation
                                          1. Commissioning of fixed building services
                                            1. Notice of completion of commissioning

                                              The Requirement G3

                                              This Approved Document deals with the following Requirement from Part G of Schedule 1 to the Building Regulations 2010.

                                              Requirement

                                              G3. (1) There must be a suitable installation for the provision of heated wholesome water or heated softened wholesome water to:

                                              (a) any washbasin or bidet provided in or adjacent to a room containing a sanitary convenience;

                                              (b) any washbasin, bidet, fixed bath and shower in a bathroom; and

                                              (c) any sink provided in any area where food is prepared.

                                              (2) A hot water system, including any cistern or other vessel that supplies water to or receives expansion water from a hot water system, shall be designed, constructed and installed so as to resist the effects of temperature and pressure that may occur either in normal use or in the event of such malfunctions as may reasonably be anticipated, and must be adequately supported.

                                              (3) A hot water system that has a hot water storage vessel shall incorporate precautions to:

                                              (a) prevent the temperature of the water stored in the vessel at any time exceeding 100˚C; and

                                              (b) ensure that any discharge from safety devices is safely conveyed to where it is visible but will not cause a danger to persons in or about the building.

                                              (4) The hot water supply to any fixed bath must be so designed and installed as to incorporate measures to ensure that the temperature of the water that can be delivered to that bath does not exceed 48˚C.

                                              Limits On Application

                                              Requirement G3(3) does not apply to a system which heats or stores water for the purposes only of an industrial process.

                                              Requirement G3(4) applies only when a dwelling is—

                                              (a) erected;

                                              (b) formed by a material change of use within the meaning of regulation 5(a) or (b).

                                              Performance

                                              In the Secretary of State’s view Requirement G3(1) will be met if:

                                              a. the installation conveys hot water to the sanitary appliances and locations specified in the requirement without waste, misuse or undue consumption of water; and

                                              b. the water supplied is heated wholesome water or heated softened water.

                                              In the Secretary of State’s view Requirement G3(2) will be met if all components of the hot water system including any cistern that supplies water to, or receives expansion water from the hot water system continues to safely contain the hot water:

                                              a. during normal operation of the hot water system;
                                              b. following failure of any thermostat used to control temperature; and
                                              c. during operation of any of the safety devices fitted in accordance with paragraph G3(3).

                                              In the Secretary of State’s view Requirement G3(3) will be met for a hot water storage system that has a vented storage vessel if:

                                              a. the storage vessel has a suitable vent pipe connecting the top of the vessel to a point open to the atmosphere above the level of the water in the cold water storage cistern and over it; and,
                                              b. in addition to any thermostat, either the heat source, or the storage vessel is fitted with a device that will prevent the temperature of the stored water at any time exceeding 100˚C; and
                                              c. the hot water system has pipework that incorporates a provision for the discharge of hot water from the safety devices to an appropriate place open to the atmosphere where it will cause no danger to persons in or about the building.

                                              In the Secretary of State’s view Requirement G3(3) will be met for a hot water system that has an unvented storage vessel if:

                                              a. the storage vessel has at least two independent safety devices such as those that release pressure and so prevent the temperature of the stored water at any time exceeding 100˚C in addition to any thermostat; and
                                              b. the hot water system has pipework that incorporates a provision for the discharge of hot water from safety devices to be visible at some point and safely conveys it to an appropriate place open to the atmosphere where it will cause no danger to persons in or about the building.

                                              In the Secretary of State’s view Requirement G3(4) will be met if:

                                              the hot water outlet temperature is appropriate for the appliance being served, and any device to limit the maximum temperature that can be
                                              supplied at the outlet can not be easily altered by building users.

                                              General

                                              3.1 The delivered hot water can be considered as heated wholesome water or heated softened wholesome water where:

                                              a. the cold water supply to the hot water system is wholesome or softened wholesome; and

                                              b.the installation complies with the requirements  of the Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148 as amended).

                                              3.2 The Water Supply (Water Fittings) Regulations make provision for preventing contamination, waste, misuse, undue consumption and erroneous measurement of water supplied by a water undertaker or licensed water supplier. Guidance on the application of the Water Supply (Water Fittings) Regulations can be found in the Water Regulations Guide published by the Water Regulations Advisory Scheme.

                                              3.3 Attention is also drawn to the requirements of the Gas Safety (Installation and use) Regulations 1994 (SI 1994/1886) for all gas installation work.

                                              3.4 Electrical work associated with hot water systems should be carried out in accordance with BS7671:2008 Requirements for electrical installations (IEE Wiring Regulations 17th Edition).

                                              3.5 For installations in dwellings and associated buildings, attention is drawn to Building Regulations 2000 Schedule 1 Part P (Electrical safety – Dwellings) and to Approved Document P.

                                              3.6 For workplaces and premises controlled in connection with a trade, business or other undertaking, attention is also drawn to the HSC publication Legionnaires’ Disease: Control of Legionella Bacteria in Water Systems. Approved code of practice and guidance. L8, Health and Safety Commission 2000. ISBN 0 7176 1772 6.

                                              3.7 Pipework should be designed and installed in such a way as to minimise the transfer time between the hot water storage system and hot water outlets.

                                              3.8 The safety requirements for hot water systems used solely for supplying water for industrial processes is contained in the Pressure Systems Safety Regulations 2000 (SI 2000/128) and further guidance is available in Safety of pressure systems. Pressure Systems Safety Regulations 2000. Approved Code of Practice L122 HSE Books 2000. ISBN 0 7176 1767 X.

                                              Provision of hot water supply

                                              3.9 The Requirement G3 only requires the provision of a hot water supply to:

                                              a. any washbasin provided in association with a sanitary convenience in accordance with G4(2);

                                              b. any washbasin, bidet, fixed bath or shower in a bathroom in a dwelling or provided for rooms for residential purposes, provided in accordance with G5;

                                              c. any sink in a food preparation area, provided in accordance with G6.

                                              There is no requirement under the Building Regulations to provide hot water to other washing facilities, but there may be such requirements under other legislation (see paragraphs 4.3, 4.4 and 6.4).

                                              Design and installation of directly or indirectly heated hot water storage systems

                                              General

                                              3.10 Hot water storage systems should be designed and installed in accordance with BS 6700:2006 + A1:2009 Specification for design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages or BS EN 12897:2006 Water supply. Specification for indirectly heated unvented (closed) storage water heaters.

                                              3.11 Hot water storage vessels should conform to BS 853-1:1996 Specification for vessels for use in heating systems. Calorifiers and storage vessels for central heating and hot water supply, BS 1566- 1:2002 Copper indirect cylinders for domestic purposes. Open vented copper cylinders. Requirements and test methods, or BS 3198:1981 Specification for copper hot water storage combination units for domestic purposes or other relevant national standards as appropriate.

                                              Vented hot water storage systems

                                              3.12 Vented hot water storage systems should incorporate a vent pipe of an adequate size, but not less than 19mm internal diameter, connecting the top of the hot water storage vessel to a point open to the atmosphere above and over the level of the water in the cold water storage cistern.

                                              3.13 In addition to the vent pipe referred to in 3.12 and any thermostat provided to control the temperature of the stored water to a desired temperature, vented hot water storage systems should incorporate either:

                                              a. for all direct heat sources, a non-self-resetting energy cut-out to disconnect the supply of heat to the storage vessel in the event of the storage system overheating; and,

                                              for all indirect heat sources, an overheat cut-out to disconnect the supply of heat to the storage vessel in the event of the stored water overheating so that the temperature of the stored water does not exceed 100°C; or

                                              b. an appropriate safety device, for example, a temperature relief valve or a combined temperature and pressure relief valve to safely discharge the water in the event of significant over heating.

                                              3.14 Vent pipes should discharge over a cold water storage cistern conforming to BS 417- 2:1987 Specification for galvanized low carbon steel cisterns, cistern lids, tanks and cylinders. Metric units; or BS 4213:2004 Cisterns for domestic use. Cold water storage and combined feed and expansion (thermoplastic) cisterns up to 500 litres. Specification; as appropriate.

                                              3.15 The cold water storage cistern into which the vent pipe discharges should be supported on a flat, level, rigid platform which is capable of safely withstanding the weight of the cistern when filled with water to the rim and fully supporting the bottom of the cistern over the whole of its area. The platform should extend a minimum of 150mm in all directions beyond the edge of the maximum dimensions of the cistern.

                                              Note: Where an existing metal cistern is replaced, or a plastic cistern is replaced by one with larger dimensions, the existing support should be upgraded, as necessary, with one in accordance with paragraph 3.15.

                                              3.16 The cistern should be accessible for maintenance, cleaning and replacement.

                                              Unvented hot water storage systems – all systems

                                              3.17 To minimize the danger from excessive pressure, unvented hot water storage systems should incorporate a minimum of two independent safety devices. These shall be in addition to any thermostat provided to control the desired temperature of the stored water. The selection of safety devices should take account of the physical location of the devices, and the design, configuration, location of components and performance characteristics of the system to which they are attached.

                                              3.18 An acceptable approach might consist of:

                                              a. a non self-resetting energy cut-out to disconnect the supply of heat to the storage vessel in the event of the storage system over-heating; and

                                              b. a temperature relief valve or a combined temperature and pressure relief valve to safely discharge the water in the event of serious over-heating.

                                              Alternative approaches to this are acceptable provided that they provide an equivalent degree of safety.

                                              Note: See 3.35 for suitability of devices for primary thermal stores

                                              3.19 Water heaters with a capacity of 15 litres or less that have appropriate safety devices for temperature and pressure will generally satisfy the requirement set out in G3(3).

                                              Unvented hot water storage systems – systems up to 500 litres capacity and 45kW power input

                                              3.20 Paragraphs 3.21 to 3.24 are in addition to the provisions of 3.17 above.

                                              3.21 If an indirect supply of heat to an unvented hot water storage system incorporates a boiler, the energy cut-out may be on the boiler.

                                              3.22 Any unvented hot water storage system up to 500 litres and less than 45kW should be in the form of a proprietary hot water storage system unit or package. The package and components should be appropriate to the circumstances in which they are used and should satisfy an appropriate standard that will ensure the requirements of regulation G3(2) and G3(3) will be met (e.g. BS EN 12897:2006 Water Supply. Specification for indirectly heated unvented (closed) hot water storage systems or BS 6700:2006 + A1:2009 Design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages).

                                              3.23 Any unvented hot water storage system unit or package should be indelibly marked with the following information:

                                              a. the manufacturer’s name and contact details;

                                              b. a model reference;

                                              c. the rated storage capacity of the storage water heater;

                                              d. the operating pressure of the system and the operating pressure of the expansion valve;

                                              e. relevant operating data on each of the safety devices fitted; and

                                              f. the maximum primary circuit pressure and flow temperature of indirect hot water storage system units or packages.

                                              3.24 In addition, the following warning should be indelibly marked on the hot water storage system unit or package so that it is visible after installation:

                                              Warning to user

                                              Warning to user

                                               

                                              Unvented hot water storage systems – systems over 500 litres capacity or over 45kW power input

                                              3.25 Paragraph 3.26 and 3.27 are in addition to the provisions of 3.17 above.

                                              3.26 Systems over 500 litres capacity will generally be bespoke designs for specific projects and as such are inappropriate for approval by a third party accredited product conformity certification scheme. Where this is the case, the unvented hot water storage system should be designed to the safety requirements in 3.17 by an appropriately qualified engineer.

                                              3.27 Any unvented hot water storage system having a power input of more than 45kW, but a capacity of 500 litres or less should be in the form of a proprietary hot water storage system unit or package. The package and components should be appropriate to the circumstances in which they are used and should satisfy an appropriate standard that will ensure the requirement of regulation G3(2) and G3(3) will be met (e.g. BS EN 12897:2006 Water Supply. Specification for indirectly heated unvented (closed) hot water storage systems or BS 6700:2006 + A1:2009 Design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages).

                                              Safety devices

                                              Non-self-resetting energy cut-outs

                                              3.28 Non-self-resetting energy cut-outs may only be used where they would have the effect of instantly disconnecting the supply of energy to the storage vessel.

                                              3.29 Non-self-resetting energy cut-outs should conform to:

                                              a. BS EN 60335-2-73:2003 Specification for safety of household and similar electrical appliances. Particular requirements. Fixed immersion heaters and BS EN 60730-2-9:2002 Automatic electrical controls for household and similar use. Particular requirements for temperature sensing control; or

                                              b. BS EN 257:1992 Mechanical thermostats for gas-burning appliances.

                                              3.30 Where a non self-resetting energy cut- out operates indirectly on another device (see paragraph 3.18) to interrupt the supply of heat (e.g. it is wired up to a motorised valve or some other suitable device to shut off the flow to the primary heater), the energy cut-out should comply with the relevant European Standard (see paragraph 3.29) or the supplier or installer should be able to demonstrate that the device has equivalent performance to that set out in relevant standards.

                                              3.31 Where an electrical device is connected to the energy cut-out, such as a relay or motorised valve, the device should operate to interrupt the supply of energy if the electrical power supply is disconnected.

                                              3.32 Where there is more than one energy cut- out (see paragraph 3.35), each non-self-resetting energy cut-out should be independent (e.g. each should have a separate motorised valve and a separate temperature sensor).

                                              3.33 Where an energy cut-out is fitted as set out in paragraphs 3.13 a) or 3.18, each heat source should have a separate non self-resetting energy cut-out.

                                              Temperature and pressure relief devices

                                              3.34 Where relevant, appropriate pressure, temperature or temperature and pressure- activated safety devices should be fitted in addition to a safety device such as an energy cut-out.

                                              3.35 Temperature relief valves and combined temperature and pressure relief valves should not be used in systems which have no provision to automatically replenish the stored water (e.g. unvented primary thermal storage vessels). In such cases there should be a second non-self- resetting energy cut-out independent of the one provided in accordance with paragraph 3.18(a).

                                              3.36 Temperature relief valves should conform to relevant national standards such as BS 6283- 2:1991 Safety and control devices for use in hot water systems. Specifications for temperature relief valves for pressures from 1 bar to 10 bar. Combined temperature and pressure relief valves should conform to BS EN 1490:2000 Building valves. Combined temperature and pressure relief valves. Tests and Requirements.

                                              3.37 Temperature relief valves (see paragraph 3.18) should be sized to give a discharge rating at least equal to the total power input to the hot water storage system, when measured in accordance with Appendix F of BS 6283-2:1991 or BS EN 1490:2000.

                                              3.38 Temperature relief valve(s) or combined temperature and pressure relief valve(s) (see paragraph 3.18) should be located directly on the storage vessel, such that the stored water does not exceed 100ºC.

                                              3.39 In hot water storage system units and packages, the temperature relief valve(s) (see paragraph 3.18) should be:

                                              a. factory fitted and should not be disconnected other than for replacement; and

                                              b.not relocated in any other device or fitting installed.

                                              3.40 The safety and performance of an unvented system is dependent on the choice of system and safety devices appropriate for the location and correct installation of the system. Building owners and occupiers should therefore take care to choose installers who have the necessary skills to carry out this work. These skills can be demonstrated for example, by registration with a competent person scheme for this type of work or by the holding of a current registered operative skills certification card for unvented hot water systems.

                                              3.41 The installation of an unvented system is notifiable building work which must be notified to the BCB before work commences. The BCB may then check to make sure the work is safe and meets current energy efficiency requirements.

                                              3.42 If the installer is registered with a competent person scheme for the installation of unvented hot water systems it will not be necessary for the work to be notified in advance to the BCB. Installers registered with such schemes will self-certify that the work complies with all relevant requirements in the Building Regulations and the building owner/occupier will be given a building regulations certificate of compliance which is usually issued by the competent person scheme operator.

                                              Electric water heating

                                              3.43 Electric fixed immersion heaters should comply with the provisions of BS EN 60335-2-73:2003 Household and similar electrical appliances. Safety. Particular requirements for fixed immersion heaters.

                                              3.44 Electric instantaneous water heaters should comply with the provisions of BS EN 60335-2-35:2002 Specification for safety of household and similar electrical appliances.

                                              3.45 Electric storage water heaters should comply with the provisions of BS EN 60335- 2-21:2003 Household and similar electrical appliances. Safety. Particular requirements for storage water heaters.

                                              Solar water heating

                                              3.46 Factory-made solar water heating systems should comply with the provisions of BS EN 12976-1:2006 Thermal solar systems and components. Factory made systems. General requirements.

                                              3.47 Other solar water heating systems should comply with the provisions of prEN/TS 12977- 1:2008 Thermal solar systems and components. Custom built systems. General requirements for solar water heaters and combi systems, or BS 5918:1989 British Standard Code of Practice for Solar heating systems for domestic hot water as appropriate. Further guidance is available in CIBSE Guide G, Public Health Engineering and CIBSE technical guide Solar Heating Design and Installation.

                                              3.48 Where solar water heating systems are used, an additional heat source should be available.

                                              Note: The additional heat source should be used, when necessary, to maintain the water temperature to restrict microbial growth.

                                              3.49 As some solar hot water systems operate at elevated temperatures and pressures, and so all components should be rated to the appropriate temperatures and pressures.

                                              Discharge pipes from safety devices

                                              Discharge pipe D1

                                              3.50 Safety devices such as temperature relief valves or combined temperature and pressure relief valves (see paragraphs 3.13 or 3.18) should discharge either directly or by way of a manifold via a short length of metal pipe (D1) to a tundish.

                                              3.51 The diameter of discharge pipe (D1) should be not less than the nominal outlet size of the safety device, e.g. temperature relief valve.

                                              3.52 Where a manifold is used it should be sized to accept and discharge the total discharge from the discharge pipes connected to it.

                                              3.53 Where valves other than a temperature and pressure relief valve from a single unvented hot water system discharge by way of the same manifold that is used by the safety devices, the manifold should be factory fitted as part of the hot water storage system unit or package.

                                              Tundish

                                              3.54 The tundish should be vertical, located in the same space as the unvented hot water storage system and be fitted as close as possible to, and lower than, the safety device, with no more than 600mm of pipe between the valve outlet and the tundish (see Diagram 1).

                                              Note: To comply with the Water Supply (Water Fittings) Regulations, the tundish should incorporate a suitable air gap.

                                              3.55 Any discharge should be visible at the tundish. In addition, where discharges from safety devices may not be apparent, e.g. in dwellings occupied by people with impaired vision or mobility, consideration should be given to the installation of a suitable safety device to warn when discharge takes place, e.g. electronically operated.

                                              Discharge pipe D2

                                              3.56 The discharge pipe (D2) from the tundish should:

                                              a. have a vertical section of pipe at least 300mm long below the tundish before any elbows or bends in the pipework (see Diagram 1); and

                                              b. be installed with a continuous fall of at least 1 in 200 thereafter.

                                              3.57 The discharge pipe (D2) should be made of:

                                              a. metal; or

                                              b. other material that has been demonstrated to be capable of safely withstanding temperatures of the water discharged and is clearly and permanently marked to identify the product and performance standard (e.g. as specified in the relevant part of BS 7291- 1:2006 Thermostatic pipes and fittings for hot and cold water for domestic purposes and heating installations in buildings. General requirements).

                                              3.58 The discharge pipe D2 should be at least one pipe size larger than the nominal outlet size of the safety device unless its total equivalent hydraulic resistance exceeds that of a straight pipe 9m long, i.e. for discharge pipes between 9m and 18m the equivalent resistance length should be at least two sizes larger than the nominal outlet size of the safety device; between 18 and 27m at least 3 sizes larger, and so on; bends must be taken into account in calculating the flow resistance. See Diagram 1, Table 1 and the worked example.

                                              Note: An alternative approach for sizing discharge pipes would be to follow Annex D, section D.2 of BS 6700:2006 + A1:2009 Specification for design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages.

                                              1 Typical discharge pipe arrangement

                                              1 Typical discharge pipe arrangement

                                              Table 3.1 Sizing of copper discharge pipe 'D2' for common temperature relief valve outlet sizes

                                              Table 3.1 Sizing of copper discharge pipe ‘D2’ for common temperature relief valve outlet sizes

                                              Worked example:
                                              The example below is for a G½ temperature relief valve with a discharge pipe (D2) having 4 No. 22mm elbows and length of 7m from the tundish to the point of discharge.

                                              From Table 3.1:
                                              Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from a G½ temperature relief valve is: 9.0m
                                              Subtract the resistance for 4 No. 22mm elbows at 0.8m each = 3.2m

                                              Therefore the maximum permitted length equates to 5.8m which, is less than the actual length of 7m therefore calculate the next largest size.

                                              Maximum resistance allowed for a straight length of 28mm copper discharge pipe (D2) from a G½ temperature relief valve is: 18m

                                              Subtract the resistance for 4 No. 28mm elbows at 1.0m each = 4m

                                              Therefore the maximum permitted length equates to: 14m

                                              As the actual length is 7m, a 28mm (D2) copper pipe will
                                              be satisfactory.

                                              3.59 Where a single common discharge pipe serves more than one system, it should be at least one pipe size larger than the largest individual discharge pipe (D2) to be connected.

                                              3.60 The discharge pipe should not be connected to a soil discharge stack unless it can be demonstrated that the soil discharge stack is capable of safely withstanding temperatures of the water discharged, in which case, it should:

                                              a. contain a mechanical seal, not incorporating a water trap, which allows water into the branch pipe without allowing foul air from the drain to be ventilated through the tundish;

                                              b. be a separate branch pipe with no sanitary appliances connected to it;

                                              c. if plastic pipes are used as branch pipes carrying discharge from a safety device, they should be either polybutalene (PB) or cross- linked polyethylene (PE-X) complying with national standards such as Class S of BS 7291-2:2006 or Class S of BS 7291-3:2006 respectively; and

                                              d. be continuously marked with a warning that no sanitary appliances should be connected to the pipe.

                                              Notes: 

                                              1. Plastic pipes should be joined and assembled with fittings appropriate to the circumstances in which they are used as set out in BS EN ISO 1043-1:2002 Plastics. Symbols and abbreviated terms. Basic polymers and their special characteristics.
                                              2. Where pipes cannot be connected to the stack it may be possible to route a dedicated pipe alongside or in close proximity to the discharge stack.

                                              Termination of discharge pipe

                                              3.61 The discharge pipe (D2) from the tundish should terminate in a safe place where there is no risk to persons in the vicinity of the discharge.

                                              3.62 Examples of acceptable discharge arrangements are:

                                              a. to a trapped gully with the end of the pipe below a fixed grating and above the water seal;

                                              b. downward discharges at low level; i.e. up to 100mm above external surfaces such as car parks, hard standings, grassed areas etc. are acceptable providing that a wire cage or similar guard is positioned to prevent contact, whilst maintaining visibility; and,

                                              c. discharges at high level: e.g. into a metal hopper and metal downpipe with the end of the discharge pipe clearly visible or onto a roof capable of withstanding high temperature discharges of water and 3m from any plastic guttering system that would collect such discharges.

                                              3.63 The discharge would consist of high temperature water and steam. Asphalt, roofing felt and non-metallic rainwater goods may be damaged by such discharges.

                                              Prevention of excessive temperatures

                                              3.64 Where the operating temperature of domestic hot water in the storage vessel in a dwelling is capable of exceeding 80ºC under normal operating conditions (a situation that may occur in vessels used as heat stores and those connected to solar heat collectors or solid fuel boilers that do not have intervening controls between the boiler and the vessel containing the hot water) the outlet from the storage vessel should be fitted with a device, such as an in-line hot water supply tempering valve in accordance with BS EN 15092:2008 Building Valves. In-line hot water tempering valves, to ensure that the temperature supplied to the domestic hot water distribution system does not exceed 60ºC.

                                              Prevention of scalding

                                              3.65 The hot water supply temperature to a bath should be limited to a maximum of 48ºC by use of an in-line blending valve or other appropriate temperature control device, with a maximum temperature stop and a suitable arrangement of pipework.

                                              3.66 The acceptability of in-line blending valves can be demonstrated by compliance with the relevant European Standard such as BS EN 1111:1999 Sanitary tapware. Thermostatic mixing valves (PN 10). General technical specification or BS EN 1287:1999 Sanitary tapware. Low pressure thermostatic mixing valves. General technical specifications to demonstrate that the maximum temperature of 48ºC cannot be exceeded in operation and that the product will fail-safe (i.e. not discharge water above the maximum temperature). Such valves should not be easily altered by building users.

                                              3.67 In-line blending valves and composite thermostatic mixing valves should be compatible with the sources of hot and cold water that serve them.

                                              3.68 The length of supply pipes between in-line blending valves and outlets should be kept to a minimum in order to prevent the colonisation of waterborne pathogens. If intermittent use of the bath is anticipated, provision should be made for high temperature flushing to allow pasteurisation of the pipes and outlet fittings. Such events should be managed to prevent the risk associated with inadvertent use.

                                              Notes: 

                                              1. Further guidance on the use of in-line blending valves can be found in BRE Information paper IP14/03 Preventing hot water scalding in bathrooms: using TMVs
                                              2. In some buildings, e.g. care homes, in-line blending valves would need to meet the additional performance standards set out in NHS Estates Model specification D 08

                                              Installation

                                              3.69 Good workmanship is essential. Workmanship should be in accordance with appropriate standards such as BS 8000-15:1990 Workmanship on Building Sites Code of practice for hot and cold water services (domestic scale).

                                              Commissioning of fixed building services

                                              3.70 Water heaters require the input of energy to raise the temperature of water. It is therefore necessary to ensure their efficiency by proper installation and commissioning.

                                              3.71 Fixed building services, including controls, should be commissioned by testing and adjusting as necessary to ensure that they use no more fuel and power than is reasonable in the circumstances.

                                              3.72 Commissioning means the advancement of these systems from the state of static completion to working order to achieving compliance with Part L. For each system it includes setting-to- work, regulation (that is testing and adjusting repetitively) to achieve the specified performance, the calibration, setting up and testing of the associated automatic control systems, and recording of systems and the performance test results that have been accepted as satisfactory.

                                              3.73 Not all fixed building services will need to be commissioned. For example, with some systems it is not possible as the only controls are ‘on’ and ‘off’ settings. In other cases commissioning would be possible but in the specific circumstances would have no effect on energy use.

                                              3.74 Where commissioning is carried out it must be done in accordance with a procedure approved by the Secretary of State. For new and existing dwellings the approved procedure for hot water systems is set out in the Domestic Heating Compliance Guide; for buildings other than dwellings in CIBSE Commissioning Code M.

                                              3.75 Commissioning must be carried out in such a way as not to prejudice compliance with any applicable health and safety requirements.

                                              3.76 Commissioning is often carried out by the person who installs the system. Sometimes it may be carried out by a subcontractor or by a specialist firm. It is important that whoever carries it out follows the relevant approved procedure in doing so.

                                              Notice of completion of commissioning

                                              3.77 The Building Regulations (regulation 20C(2)) and the Building (Approved Inspectors etc.) Regulations (regulation 20(1) and (6)) require that the person carrying out the work shall give a notice to the relevant BCB that commissioning has been carried out according to a procedure approved by the Secretary of State, unless testing and adjustment is not possible, or would not affect the energy efficiency of the fixed building service.

                                              3.78 Where the work is carried out in accordance with a building notice, or full plans, or an initial notice or amendment notice, the notice of commissioning should be given not more than 5 days after the completion of the commissioning work. In other cases, for example where work is carried out by a person registered with a competent person scheme, it must be given not more than 30 days after the completion of work.

                                              3.79 Where the installation of fixed building services which require commissioning is carried out by a person registered with a competent person scheme the notice of commissioning will be given by that person.

                                              3.80 Until the BCB receives notice of commissioning it is unlikely to be satisfied that Part G has been complied with and consequently is unlikely to be able to give a completion/final certificate.