10 COMBUSTION AIR
Sufficient combustion air supply
A fireplace may be installed only in rooms, where sufficient combustion air supply is guaranteed. Normal op-
eration requires sufficient air supply using a separate combustion air connection for the fireplace.
Sufficient combustion air supply is present, when by natural means or using technical equipment a combus-
tion air volume of 12,5 m
3
per 1 kg fuel throughput can stream into a room with wood-burning fireplace over a
period of 1 hour at calculated negative pressure below 0,04 mbar (4 Pa) against outside air pressure. This is
equivalent to a speculative heating power (PLF) of 8 kW per 1 kg fuel throughput.
When other fireplaces are in operation in the same room or different rooms included in one room combina-
tion, these fireplaces require at least 1.6 m
3
of combustion air per hour for each kW of their total rated heat-
ing power. When a room combination contains only a small volume of air and the building is relatively air-
tight, a separate combustion air supply from outdoors is required.
Combustion air supply is ensured in rooms with at least one window or one door which can be opened to
outside of the building, or when these rooms are directly connected or interconnected with other rooms of
such type. Rooms considered as directly connected or interconnected, can be only parts of one apartment or
one facility of other kind. Particular attention to combustion air supply is to be paid, when exhaust fans and
other heat generators in the same room combination are operated, or when multiple heating devices are con-
nected to one single chimney.
Ventilation systems in this room combination cannot create negative pressure, which could affect the func-
tioning of the fireplace. Exhaust ventilation systems operating in the same room or room combination togeth-
er with fireplaces, can cause many problems.
Combustion air ducts
If external combustion air supply is necessary, it must be connected directly to the air supply connecting
piece of the fireplace, to prevent possible air drafts.
The combustion air duct must have sufficient cross-section. It must be laid using the shortest way and with-
out unnecessary bends, to reduce flow resistance. Combustion air duct dimensioning must be according to
EN13884; flow resistance has to be estimated by calculation and must be taken into account!
Components of combustion air duct must be made of non-flammable, dimensionally stable and abrasion re-
sistant materials (DIN 4102 A1 or Class A1(B2) according to DIN EN 13501-1); they must ensure tightness
und be accessible for inspection and cleaning.
Thermal insulation is necessary from the fire-protection point of view, if air temperatures >85°C are possible.
Temperatures below dew point can cause water condensation, therefore appropriate insulation must be
used.
For buildings with more than two storeys and when crossing fire protection walls, the construction of these
ducts must prevent fire and smoke from penetrating other fire protection zones (their components must have
a fire resistance rating of >90 minutes (F90)). See also national building law.
If the external air supply duct has a separate flap for closing, the position of this flap must be recognizable.
It must be ensured, that the external air supply flap is open until the fire is burning. Air suction grilles or flaps
cannot narrow the free cross section.
© 2021 Brunner GmbH Installation Guide KSO 33 (1.12) 17
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