From August 2005 any open-flued or flueless gas appliances encountered, which, have purpose-provided ventilation, identified as not being of adequate size will be classified as described in the Table set out below.
Further information is available here.
| From 0% to 39% of the appliance air requirement |
At Risk (AR) |
|
| From 40% to 89% of the appliance air requirement |
At Risk (AR) |
Until 1st June 2008 existing installations can be regarded as NCS, provided that the installation is otherwise operating safely. The gas user should be advised in writing that this is an interim situation that needs to be up-graded to meet current industry standards before the 1st June 2008. From this date, all installations provided with less than 90% of the required ventilation requirement will default to the AR classification. |
| From 90% to 100% of the appliance air requirement |
None |
The gas industry has determined that open-flued and flueless gas appliances provided with purpose-provided ventilation within this range of the appliance requirement are considered satisfactory. |
| Open-flue gas appliances installed in a compartment requiring purpose-provided high and low level permanent air supply; providing less than 90% of the requirement for each ventilator position |
At Risk (AR) |
Both, high and low level ventilation is required. Research has shown that the correct sizing, positioning and configuration of air vents to compartment installations is essential to prevent incomplete combustion of the appliance. However, an air supply that is less than 10% undersized is unlikely to have a detrimental affect on the safe operation of an appliance. |