Technical data

GUH RANGE PROPANE GAS FIRED UNIT HEATERS
Page 11 of 41
2.4 Air Supply
Provision must be made for the existence of an air supply in order to satisfy both combustion and
ventilation criteria.
It is a requirement that the area where the air heater is located must have a permanent air vent of
negligible resistance direct to the outside air.
Such air vents must be positioned so as not to become blocked or flooded, nor should they be placed so
as to introduce undesirable matter (e.g. flammable, volatile, or aggressive chemicals/compounds or
potentially hazardous or harmful substances) either direct from the outside, or through their proximity to
an adjacent extraction system.
The criteria necessary for establishing the minimum size of natural vents is detailed as follows;
Position of vent Area of vent direct to outside
Low level (<60kW) 9.0cm
2
per kW
Low level (>60kW) 540cm
2
+ 4,5cm
2
per kW of
(Inlet) rated input per heater
High level (<60kW) 4.5cm
2
per kW
High level (>60kW) 270cm
2
+ 2,25cm
2
per kW of
(Outlet) rated input per heater
Where mechanical ventilation is used it is a requirement that the inlet is of the mechanical type, and the
outlet is either mechanical or natural.
Caution
Systems of ventilation that employ mechanical extraction and natural inlet must not be used.
Furthermore, where the air supply is by way of a mechanical means the inlet must be positioned at low
level and be capable of providing a minimum throughput as detailed in section 7.2 of this manual.
The natural extraction air vents must have a minimum area as per the above table, and it is strongly
recommended that natural extraction vents are situated at high level.
Additionally, an automatic control interlocked to the burner must be fitted to ensure burner shutdown in
the event of airflow failure or restriction.
When the area to be heated already has an extraction system, the size of the air vent must be sized to
account for this and to maintain the required number of air changes
If the heater is to be installed within its own separate building or plant room, the above details do still
apply, as does the requirement for minimum space, further consideration should be made for free air for
recirculation to avoid the possibility of negative pressure in the plant room (see guidance notes below)
Additionally the maximum temperature within the plant room should not exceed 32DegC
Note
It is strongly recommended that BS 6230 : 1991 is referred to for further information concerning
ventilation requirements.