The standard gives details of a general scheme for the classification of such appliances according to the method of evacuating the products of combustion. It must be stressed that this scheme only concerns appliances that are intended to be installed within buildings. It does not apply to outdoor appliances.
DS/CEN/TR 1749:2009 history
2009DS/CEN/TR 1749:2009 European scheme for the classification of gas appliances according to the method of evacuation of the combustion products (types)