2.7 Ventilation and Combustion Air Requirements
This appliance is rated less than 5kW, therefore there is no mandatory requirements
for additional air unless a flue draught stabiliser is fitted then the air requirement is
15cm
2
. However, we suggest that it is advantageous to provide an air supply into the
room.
When calculating combustion air requirements for this appliance use the following
equation: 550mm
2
per each kW of rated output above 5 kW should be provided,
where a flue draught stabiliser is used the total free area shall be increased by 300mm
2
for each kW of rated output. If there is another appliance using air fitted in the same
or adjacent room, it will be necessary to provide an additional air supply.
All materials used in the manufacture of air vents should be such that the vent is
dimensionally stable, corrosion resistant, and no provision for closure. The effective
free area of any vent should be ascertained before installation. The effect of any grills
should be allowed for when determining the effective free area of any vent.
Air vents direct to the outside of the building should be located so that any air current
produced will not pass through normally occupied areas of the room.
An air vent outside the building should not be located less than the dimensions
specified within the Building Regulations and B.S. 8303: Part 1 from any part of any
flue terminal. These air vents must also be satisfactorily fire proofed as per Building
Regulations and B.S. 8303: Part 1.
Air vents in internal walls should not communicate with bedrooms, bedsits, toilets,
bathrooms or rooms containing a shower.
Air vents traversing cavity walls should include a continuous duct across the cavity.
The duct should be installed in such a manner as not to impair the weather resistance
of the cavity.
Joints between air vents and outside walls should be sealed to prevent the ingress of
moisture. Existing air vents should be of the correct size and unobstructed for the
appliance in use. If there is an extraction fan fitted in adjacent rooms where this
appliance is fitted, additional air vents may be required to alleviate the possibility of
spillage of products of combustion from the appliance/flue while the fan is in
operation. Refer to B.S. 8303 Part 1.
Where such an installation exists, a test for spillage should be made with the fan or
fans and other appliances using air in operation at full rate, (i.e. extraction fans,
tumble dryers) with all external doors and windows closed.
If spillage occurs following the above operation, an additional air vent of sufficient
size to prevent this occurrence should be installed.
