CO Alarm Selection & Positioning

Warning of Release of Carbon Monoxide

According to building regulations where a fixed combustion appliance is provided, appropriate provision should be made to detect and give warning of the release of carbon monoxide.

The regulations are clear in laying out the conditions for ensuring a CO alarm compliant with BS EN 50291 is present upon installation of a solid fuel appliance, however establishing the suitable type, position and fixing method is where confusion can exist between current appropriate standards and alarm manufacturers’ installation instructions.

Best Practice

It is important for the installer or landlord to understand the behaviour of CO emissions to assess in practice the best location of the alarm. In principle, CO has almost the same density as air and would be emitted as part of spillage of combustion products which are hot and will warm the air around the appliance.  This warmer air is likely to rise due to its buoyant characteristics, which supports best practice measures and those given within regulatory guideline in positioning the CO alarm at a high position on the wall or on the ceiling.

Product Selection – Alarm Type

A suitable alarm will have been tested to confirm it meets the necessary requirements of BS EN 50291:2010, and activate within the required time when the relevant volume of CO is detected. The alarm packaging itself will contain the relevant information, including appropriate Kitemark reference (if tested by BSI) and also confirmation of the test method standard, warning of the expected lifetime of the sensor and where incorporated stating the product includes an end of life indication.

Sealed for life vs Replaceable

There are currently three known types of alarm on the market, which are:

  • Sealed for Life: Alarms that have a fixed, sealed power source which will require complete replacement once the end of life which is normally a minimum of 5 years.
  • Replaceable battery: Alarms that have a replaceable power source.
  • Mains powered: Alarms normally powered by wired mains electricity but containing a back-up battery for mains failure events.

It is important to note that any of these three types of CO alarm are suitable for use with solid fuel installations. If they have been confirmed as meeting the requirements of BS EN 50291 then they shall incorporate a warning device to alert users when the working life of the alarm is coming to an end.

Alarm Positioning

The general provisions within ADJ and BS8303 ask that the CO alarm be positioned in a location which provides means for the immediate detection of CO upon spillage from a solid fuel appliance. Guidance in ADJ and in BS8303 is that CO alarms should be positioned as follows:

  1. On the ceiling at least 300mm from any wall or, if it is located on a wall as high up as possible (above any doors or windows) but not within 150mm of the celling.
  2. Between 1m and 3m horizontally from the appliance.

These stated parameters allow for the earliest possible detection of CO as the combustion products disperse and mix with the air within the room. In these positions the detector is also avoiding the relevant “dead zone” areas whereby the velocity of gases disperse and convect in a circular motion and do not reach the corner areas of the room. It is also important to ensure CO alarms are not located directly next to the appliance, or within areas where air disperses at a slower rate. Typically installations of solid fuel appliances are within a builder’s recess, where the flue is contained within a masonry chimney stack which protrudes slightly into the room in which the appliance is installed. Following best practice, it is also recommended for CO alarms not to be located on the side wall of the masonry stack, which again acts as a potential “dead zone”, which may increase the activation response time of the alarm as the CO disperses into the room in a radiant motion.

Affixing the Alarm

The regulations currently state that “appropriate provision shall be made to detect and give warning of the release of CO”. Having checked with the Government Department responsible, we can state that “appropriate provision” is seen as permanently affixing a suitable alarm to the wall/ceiling in an appropriate place, and that simply leaving an alarm with a customer is not seen as “appropriate provision”. It is vital for the installer to educate the consumer in the importance of the alarm, its position and what to do when the alarm sounds. This document can be used as evidence of the things to be considered and the reasoning behind the requirements. This important information can be relayed to the consumer as part of the commission and handover process.

Best Practice and Compliant Locations Where a CO Alarm Can Be Located

Supplementary Information on Selection & Positioning

Further information can be found within:

  • Clause 2.34 to 2.36 of Approved Document J
  • Supplementary product and installation standards including BS EN 50292 & BS 8303
  • Alarm Manufacturer Instructions

It is important for the general safety of the occupants that installers and landlords are selecting and positioning an alarm effectively allowing the quickest response time from the alarm for the occupants to vacate the premises.

Please note: if the CO alarm meets the requirements of BS EN 50291 and is fitted to manufacturer’s instructions this would satisfy compliance to the regulations, however the details above are a best practice guide.


HETAS – Technical Note – TN_0022 –  CO Alarm Selection & Positioning