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GUIDE TO FLUE
INSTALLATION &
REGULATIONS
There are many different regulations relating to flues and ventilation.
This document will not cover all of them but assist in obtaining information
and guidance, and provide useful and practical information.
This guide looks at common standards used to determine the requirements for flue and ventilation installation
requirements and should not be used as a sole reference for flue regulations. Please also remember to use the
installation and service manual for specific guidance for each boiler and to refer to the relevant standards.
COMMERCIAL BOILERS (70kW – 1.8MW)
BS6644
Specification for the installation and maintenance of gas-fired hot water boilers
of rated inputs between 70 kW (net) and 1.8 MW (net) (2nd and 3rd family gases).
In IE refer to I.S. 820.
IGEM UP10
Installation of flued gas appliances in industrial and commercial premises.
Building Regs Part J
Combustion appliances and heat storage, gives advice on how to comply with
Building Regulations.
Clean Air Act
A UK Parliament Act passed in response to London’s Great Smog of 1952.
(1956 Amendment)
The Act introduced a number of measures to reduce air pollution, especially by introducing ‘smoke control areas’
in some towns and cities in which only smokeless fuels could be burned. By shifting homes’ sources of heat
towards cleaner coals, electricity, and gas, it reduced the amount of smoke pollution and sulphur dioxide from
household fires. Reinforcing these changes, the Act also included measures to relocate power stations away from
cities, and for the height of some chimneys to be increased.
The Act was an important milestone in the development of a legal framework to protect the environment.
Although smog is no longer an issue, more recent editions of the Clean Air Act have maintained control of
emissions and heights of flues.
*Appliance fan also downstream of draught diverter
Where 2 or more gas fired boilers are connected to a common natural draught flue, the boilers must be installed
in the same room and have the same type of burner system. A gas fired boiler and a solid fuel or biomass boiler
must not discharge into the same flue. A gas fired boiler and a liquid fired fuel boiler can discharge into the same
flue providing they are both installed in the same room and are force draught.
Appliance type
Primary definition
Natural draught or fan draught
C type
Room sealed
Natural draught
Fan down
stream of heat
exchanger
Fan upstream of
heat exchanger
C1- appliances with a horizontal balanced flue/
inlet air ducts to outside atmosphere.
C11*
C12
C13*
C2 – appliance flue connects to a common duct
system for multi-appliance installations (the
common duct system is part of the building)
C21
C22
C23
C 3 - appliance with vertical balanced flue/inlet air
ducts to outside atmosphere.
C31
C32*
C33*
C4 – appliance with flue system that connects to
a common duct system e.g. ‘U’ duct flue system.
C41
C42
C43
C5 – appliance with a non-balanced flue/inlet air
duct system.
C51
C52
C53
C6 – appliance sold without a flue system
C61
C62
C63
C7 – appliance connected to a vertical flue to
outside atmosphere with the air ducts in the loft
(vertex)
C71
C72
C73
C8- appliance with a non-balanced flue system
with an air supply from outside atmosphere and
flued into a common duct system.
C81
C82
C83
TYPE C13
TYPE C32
TYPE C33
TYPE C13
TYPE C32
TYPE C33
TYPE C13
TYPE C32
TYPE C33
TYPE C13
TYPE C32
TYPE C33
TYPE C13
TYPE C32
TYPE C33
