BS 6644 is a key standard on installation of gas-fired hot water boilers. It specifies requirements for the installation, including design, inspection and commissioning, of gas-fired hot water boilers of net rated heat inputs exceeding 70 kW. Groups of boilers with individual net heat inputs of 70 kW or less, but with total net heat inputs in excess of 70 kW are also covered by this standard.
This standard applies to the installation of boilers that are designed to use normally distributed gases of Group H of the second family (e.g. natural gas), and gases of Group P (e.g. propane) and Group B (e.g. butane) of the third family. For the purposes of this installation standard, LPG/air mixtures are regarded as third family gases.
BS 6644 is relevant to the installation of gas-fired hot water boilers within the scope of:
a) For boilers supplied as a complete assembly, BS EN 656 or BS 5978 (all parts)
b) For boilers supplied as a complete assembly and used in multiple boiler installations whose total net heat input exceeds 70 kW, BS EN 297, BS EN 483, or BS EN 677
c) For boilers and burners delivered separately and assembled on site:
1) The boiler shell, BS EN 303-1, BS EN 12952, BS EN 12953 BS 779, BS 855, or BS 2790
2) The burner, BS EN 676
3) The assembly, BS EN 303-3 or BS 5987-1 and BS 5978-3.
It can also be used for installations that have been converted from burning other fuels to gas firing.
This standard is not appropriate for:
a) The installation of any heating or hot water supply system associated with the boiler installation
b) The installation of gas cushion systems (non diaphragm expansion vessels) intended to pressurize the hot water circuit
c) Installations in hazardous areas (these are defined in The Dangerous Substances and Explosive Atmospheres Regulations).
This amended version of BS 6644 replaces BS 6644:2005 that is now withdrawn.
