Introduction

• For detailed guidance, refer to the full version of the Technical Handbook and British Standards linked above.

Building Standards Scotland Technical Handbook – Domestic

Mandatory Standard 3.21 Combustion appliances – air for combustion

Every building must be designed and constructed in such a way that each fixed combustion appliance installation receives air for combustion and operation of the chimney so that the health of persons within the building is not threatened by the build-up of dangerous gases as a result of incomplete combustion.

3.21.1 Supply of air for combustion generally

Ventilators for combustion should be located so that occupants are not provoked into sealing them against draughts and noise… Air vents should not be located within a fireplace recess except on the basis of specialist advice.  Noise attenuated ventilators may be needed in certain circumstances.

3.21.4 Supply of air for combustion to gas-fired appliances

A gas-fired appliance installed in a room or space should have a supply of air for combustion.  An air supply should be provided in accordance with the following recommendations:
a. BS 5871-3: 2005, for a decorative fuel-effect gas appliance
b. BS 5871-2: 2005, for an inset live fuel-effect gas appliance
c. BS 5440-2: 2000, for any other gas-fired appliance.

BS 5871-3: 2005

Part 3: Decorative fuel effect gas appliances of heat input not exceeding 20 kW (2nd and 3rd family gases)

8 Ventilation

8.1 General: The appliance shall have a supply of air for combustion and the safe operation of the flue.
COMMENTARY AND RECOMMENDATIONS ON 8.1
Subclauses 8.2, 8.3, 8.4 and 8.5 specify the ventilation requirements for appliances.  It should be noted that whilst BS 5440-2 excludes decorative fuel effect gas appliances from its scope, the references given in 8.3 and 8.5 to BS 5440-2:2000 are applicable in the context in which they are specified.

8.2 Sizing: Unless the manufacturer’s instructions specifically state that purpose provided ventilation is not required, such ventilation shall be provided in the room or internal space containing the appliance.  Where purpose provided ventilation is required, the air vent free area shall be a minimum of 100 cm², or, where greater, as stated in the manufacturer’s instructions.
COMMENTARY AND RECOMMENDATIONS ON 8.2
Normally, appliances covered by this standard will require a minimum of 100 cm² of purpose provided ventilation.  However, in the case of an appliance of not greater than 7 kW input which generates a clearance flue flow not greater than 70 m³/h when tested in accordance with Annex A, an air vent may not be necessary.  The manufacturer’s instructions will provide details in such circumstances.  It should be noted that Annex A describes a laboratory test which is not for use by gas installers seeking conformity with this standard.

8.3 Location: An air vent shall not communicate directly with a builder’s opening or fireplace recess.  In areas in which radon gas has been identified as a problem, ventilation shall not be taken from below floor level (e.g. using a floor vent) or interfere in any way with remedial measures which may already be in place to prevent radon from entering the habitable part of the dwelling.

BS 5440-2:2009

Part 2: Specification for the installation and maintenance of ventilation provision for gas appliances

6.3.1 Open-flued appliance installed in a room or internal space

Where an open-flued appliance with a rated input exceeding 7 kW is installed in a room or internal space or garage, that room or internal space shall be provided with a permanent opening and an air vent with a minimum free area of 5 cm² for every kW of appliance maximum rated input in excess of 7 kW.  Ventilated underfloor space shall be considered outside air, providing the air vents supplying air to the underfloor space remain adequate (i.e. air vents have not been removed, blocked or sealed).  Underfloor air vents to gas space heaters shall not be positioned directly under the appliance and shall be in accordance with BS 5871-1, BS 5871-2, BS 5871-3 or BS 5871-4, as appropriate.

6.5 Flueless appliances

Where a flueless appliance is installed/operated in a room or internal space, that room or internal space shall be provided with air vents which communicate directly with outside air and are sized in accordance with Table 6.  Where no openable window is available, an alternative means of ventilation shall be provided in addition to the permanent air vent [see footnote A) in Table 6].
COMMENTARY ON 6.5
Where an appliance is not rigidly fixed (i.e. it is portable), ventilation in accordance with Table 6 should be provided in every room in which the appliance can be connected to the fixed pipework via a suitable self‑sealing connector (see BS 669-2).  This does not include moveable cabinet heaters which carry their own gas cylinders.

Make a gas appliance calculation

General notes: