It is good practice in the design of kitchen extraction systems to provide for the replacement of the extracted air (HVCA DW/172). If gas cooking appliances are to be used the provision of replacement air becomes an essential requirement under The Gas (Installation and Use) Regulations 1998 and BS 6173.
The most reliable method of ensuring that sufficient replacement air is introduced into a kitchen is to allow for this in the design of the extraction canopy. Our custom-made stainless steel extraction canopies can be manufactured with a full-length replacement air plenum (chamber) into which replacement air is driven by a supply fan and from which air flows into the kitchen via diffusers in the front face of the canopy.
A range of different diffuser designs are available including “eyelash” grilles which incorporate directional vanes to provide control for kitchen staff or perforated diffusers which minimise drafts.
In accordance with The BESA DW/172 our replacement air systems are designed to introduce up to 85% of the volume of extracted air into the kitchen.
We would normally include within our replacement air systems for filtration of dust out of the incoming air with a bag or panel filter and the prevention of condensation on the replacement air plenum by the internal insulation of this component of the canopy.
Where canopy design is constrained by the building structure with low ceiling heights or complex duct runs it is sometimes necessary to specify a replacement air system which is independent of the extract canopy.
This may be mechanical (fan-driven) or, if only low air volumes are required, a passive venting system via fixed wall, door or window transfer grilles. The introduction of external air into a kitchen can cause draughts and undesirable cooling of the kitchen in winter and so a number of our replacement air systems are provided with a heater battery (either electric or low pressure hot water powered) or air handling unit to ensure that air entering the kitchen is maintained above a pre-set temperature.
