Monday 9 May 2011

Stove Ventilation

The regulations covering ventilation for stoves as of 1st Oct 2010.

Approved Document J Section 1.5: Appliance compartments that enclose open-flued combustion appliances should be provided with vents large enough to admit all of the air required by the appliance for combustion and proper flue operation, whether the compartment draws its air from a room or directly from outside.

Approved Document J Section 1.16: Discomfort from cold draughts can be avoided by supplying air directly to appliances, locating vents close to appliances (for example by using floor vents), by drawing air from intermediate spaces such as hallways or by ensuring good mixing of incoming cold air by placing external air vents close to ceilings. In noisy areas it may be necessary to install noise-attenuated ventilators to limit the entry of noise into the building. Transfer or connecting ventilation should be at low level to reduce the transfer of smoke in the event of a fire and otherwise meet the guidance given in Approved Document B.

Stoves intended for a family living space such as family/dining/kitchens or in a room that has no door in an opening between this area and the kitchen (viewed by Building Regulations as one space), the provision of mechanical extract ventilation over the hob will depend largely on the model of the log burner as the mechanical extract and natural ventilation required to the log burner may cancel each other out. Please let your designer know the make and model of the chosen burner.

Mechanical extract for the kitchen end may be replaced by passive stack ventilation. PSV is a ventilation system using ducts from terminals in the ceiling to terminals on the roof that extract air to outside by a combination of the natural stack effect and the pressure effects of wind passing over the roof. Attention should be paid to Approved Document F, Table 5.2b.

Stoves need a supply of air for combustion, and to evacuate the flue gases otherwise they will not work. Without an air supply the stove will not light and smoke is likely to pour out into the house. The smoke will not be able to be drawn up the chimney as this requires air movement up through the chimney which is not possible if there is no source of air.

Ventilation rates to the stove are now based on the air permeability of the house as well as the rated output of the stove.

Approved Document J, Section 2 Table 1:

Other appliance, such as a stove, cooker or boiler, with a flue draught stabiliser.

Permanently open vents as below:

If design air permeability >5.0m3/(h.m2) then 300mm2/kW for first 5kW of appliance rated output 850mm2/kW for balance of appliance rated output If design air permeability≤5.0m3/(h.m2) then 850mm2/kW of appliance rated output.

Other appliance, such as a stove, cooker or boiler, with no flue draught stabiliser.

Permanently open vents as below:

If design air permeability >5.0m3/(h.m2) then 550mm2/kW of appliance rated output above 5kW

If design air permeability ≤5.0m3/(h.m2) then 550mm2 per kW of appliance rated output.

It is unlikely that a dwelling constructed prior to 2008 will have an air permeability of less than 5.0m3/(h.m2) at 50 Pa unless extensive measures have been taken to improve air-tightness.

The ventilation air for a stove may be drawn directly through an external air duct if the stove has a spigot for connecting the air duct. An increasing number of stoves (for example many Westfire and Morso stoves) have provision for an external air supply to be connected to the stove.

The vent should be placed in such a way that it cannot be easily blocked and so that you are not tempted to block it off to reduce draughts or noise.

If there is a mesh to guard against pest/mice etc coming through the vent then the mesh size must be no less than 5mm.

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