Building standards technical handbook 2022: non-domestic

Guidance on achieving the standards set in the Building (Scotland) Regulations 2004. This handbook applies to a building warrant submitted on or after 1 June 2022 and to building work which does not require a warrant commenced from that date.

3.17 Combustion appliances – safe operation

Mandatory Standard

Standard 3.17

Every building must be designed and constructed in such a way that each fixed combustion appliance installation operates safely.

3.17.0 Introduction

The guidance to this standard covers general issues and should be read in conjunction with Standards 3.18 to 3.22 that are intended to reduce the risk from combustion appliances and their flues from:

  • endangering the health and safety of persons in and around a building

  • compromising the structural stability of a building, and

  • causing damage by fire.

The incorrect installation of a heating appliance or design and installation of a flue can result in situations leading directly to the dangers noted above.

The installation of mechanical extract fans is not in itself dangerous but guidance on their use has been included under this standard as their use with open-flued appliances can cause problems. Extract fans lower the pressure in a building and this can cause the spillage of combustion products from open-flued appliances. This can occur even if the appliance and the fan are in different rooms. Combustion appliances therefore should be capable of operating safely whether or not any fan is running (see clause 3.17.8).

Biomass as a solid fuel comes in different forms with the most common being woody biomass which can be used in a wide range of appliances such as individual room heaters to large scale heating boilers and combined heat and power (CHP) generation plants.

Wood burning appliance technologies are such that modern appliances are now designed to efficiently burn specific wood fuel types including logs, wood chips, wood pellets and wood thinnings.

Guidance that is given for solid fuel appliance installations may also be appropriate for biomass appliance installations however depending on the complexity of the system there may additional issues to consider particularly in relation to safety, noise, flue sizing, ventilation and fuel storage.

There is other legislation that relates to gas fittings, appliances, installations and their maintenance and to the competency of persons who undertake such work (see clause 3.17.6).

Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

3.17.1 Combustion appliance installations generally

This guidance has been prepared mainly with domestic sized installations in mind, such as those comprising space and water heating or cooking facilities, including their flues. The guidance also includes flueless appliances such as gas cookers.

The guidance to Standards 3.17 to 3.22 therefore applies to solid fuel appliances with an output rating not more than 50kW, oil-firing appliances with an output rating not more than 45kW and gas-fired appliances with a net input rating not more than 70kW.

3.17.2 Large combustion appliance installations

It is expected that specialists will design non-domestic sized combustion appliance installations in accordance with general standards provided in the Practice Standards produced by the British Standards Institution (BS EN or BS) and the Institution of Gas Engineers or the Design Guide produced by the Chartered Institution of Building Service Engineers (CIBSE). A few large dwellings may require such installations.

The following guidance therefore, may not be relevant to solid fuel appliances with an output rating more than 50kW, oil-firing appliances with an output rating more than 45kW and gas-fired appliances with a net input rating more than 70kW.

3.17.3 Small combustion appliance installations

An installation is only as good as its weakest part and it is necessary to ensure that the entire installation is safely constructed and installed.

Where a combustion appliance installation is intended to operate with more than one type of fuel, for example a gas appliance as a stand-by to a solid fuel appliance, each component should be constructed and installed to meet the most onerous requirement of the relevant fuel.

3.17.4 Solid fuel appliance installations

Solid fuel appliances should be fit for purpose for the type of fuel burnt and all solid fuel appliance installations should be constructed and installed carefully to ensure that the entire installation operates safely. Installations should be constructed and installed in accordance with the requirements of BS 8303: Parts 1 to 3: 1994.

The Heating Equipment Testing and Approval Scheme (HETAS) is an independent organisation for setting standards of safety, efficiency and performance for testing and approval of solid fuels, solid mineral fuel and wood burning appliances and associated equipment and services for the UK solid fuel domestic heating industry. It operates a registration scheme for competent Engineers and Companies working in the domestic solid fuel market. The Official Guide to Approved Solid Fuel Products and Services published by HETAS Ltd contains a list of Registered Heating Engineers deemed competent in the various modules listed, e.g. for the installation, inspection and maintenance of solid fuel appliances.

There are other organisations representing the solid fuel industry but neither they nor HETAS have a mandatory status. The CIBSE Knowledge Series KS10 ‘Biomass Heating’ provides guidance on installation issues relative to biomass systems fuelled by wood chips and pellets with a heating demand of 50kW to 5000kW.

3.17.5 Oil-firing appliance installations

The Oil Firing Technical Association (OFTEC) sets equipment standards, installation practice and technician competence within the oil firing industry. It publishes technical guidance, operates a registration scheme for competent technicians and companies and an equipment testing and approval scheme. OFTEC schemes and technical advice only have mandatory status when specifically referred to in legislation.

Oil-firing appliances should be constructed, installed, commissioned and serviced carefully to ensure that the entire installation operates safely. Oil-firing equipment should be suitable for its purpose and the class of oil used in the installation. Oil-firing equipment should comply with the relevant OFTEC standard and should be installed in accordance with the recommendations in BS 5410: Parts 1 and 2.

Fire valves should be fitted so as to cut off the supply of oil remotely from the combustion appliance in the event of a fire starting in or around the appliance. The valve should be located externally to the building. The valve should be fitted in accordance with the recommendations in Section 8.3 of BS 5410: Part 1: 1997 and OFTEC Technical Book 3.

3.17.6 Gas-fired appliance installations

In addition to the functional standards, gas-fired appliance installations must also comply with the Gas Safety (Installation and Use) Regulations 1998. These regulations require that, amongst others, gas-fired installations are installed by a competent person. Guidance on the individual competency required in given in the Health and Safety Commission’s Approved Code of Practice ‘Standards of Training in Safe Gas Installations’. The Gas Safe Register operates a registration scheme for gas businesses and individual gas operatives to ensure that they carry out their work in a competent manner. It is the only scheme recognised by the Health and Safety Executive (HSE) that complies with the Gas Safety (Installation and Use) Regulations 1998.

The Gas Safety (Installations and Use) Regulations 1998 regulates gas installations while the Gas Appliance (Safety) Regulations 1995 address the product safety of appliances.

3.17.7 Labelling

Where a hearth, fireplace (including a flue box), or system chimney is provided, extended or altered, information essential to the correct application and use of these facilities should be permanently posted in the building to alert future workmen to the specification of the installed system. This also applies to cases where a flue liner is provided as part of refurbishment work.

The labels should be indelibly marked and contain the following information:

  1. the location of the hearth, fireplace (or flue box) or the location of the beginning of the flue

  2. a chimney designation string in accordance with BS EN 1443: 2003 (see clause 3.18.2) for products whose performance characteristics have been assessed in accordance with a European Standard and that has been supplied and marked with a designation as described in the relevant European Standard

  3. the category of the flue and generic types of appliance that can safely be accommodated

  4. the type and size of the flue (or its liner)

  5. the installation date.

Labels should be located in a position that will not easily be obscured such as adjacent to:

  • the gas or electricity meter, or

  • the water supply stopcock, or

  • the chimney or hearth described.

A label, should be provided similar to the example below:

Figure 3.35. Safety label

Safety label

3.17.8 Extract fans

Extract fans lower the pressure in a building and may cause the spillage of combustion products from open-flued appliances. This can occur even if the appliance and the fan are in different rooms. Ceiling fans produce currents and hence local depressurisation that can also cause the spillage of flue gases. The presence of some fans may be obvious, such as those on view in kitchens, but others may be less obvious. Fans installed in appliances such as tumble dryers or other open-flued combustion appliances can also contribute to depressurisation. Fans may also be provided to draw radon gas out of the underbuilding.

In buildings where it is intended to install open-flued combustion appliances and extract fans, the combustion appliances should be able to operate safely whether or not the fans are running.

The installation of extract fans should be in accordance with the guidance below, and should be tested to show that combustion appliances operate safely whether or not fans are running:

  1. for solid fuel appliances, extract ventilation should not generally be installed in the same room or alternatively seek further guidance from HETAS. However in certain cases, such as large rooms where there is free flowing replacement air, a fan may be fitted provided a satisfactory spillage test is carried out in accordance with BRE Information Paper IP 7/94

  2. for oil-firing appliances, limit fan capacities as described in OFTEC Technical Book 3 and then carry out flue draught interference tests as described in Book 3 or BS 5410: Part 1: 1997

  3. for a gas-fired appliance, where a kitchen contains an open-flued appliance, the extract rate of the kitchen extract fan should not exceed 20 litres/second. To check for safe operation of the appliance(s) the recommendations in clause of BS 5440: Part 1: 2000 should be followed.

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