This document covers the measurements of the emissions of carbon monoxide (CO) and nitrogen oxides (NOX) produced by the combustion of gaseous fuel in domestic appliances. It is also possible to adapt it to liquid fuel appliances. It explains how to correct the measured values obtained at the testing conditions of temperature, humidity and gas used into the reference conditions, as well as their conversion to different aeration factor expressed as %O2 in the dry products of combustion. The document also contains information on the types of sampling probes, mainly their form and their dimensions, which depend on the type of flue gas system. It also gives detailed information on the sampling of the flue gas to be analysed, the transport / transfer lines and their components, and the materials recommended for their construction. This document contains hints on the calculation of the uncertainties and the parameters to be considered in the whole analysis chain from the sampling probe to the analysers including the calibration gases. The calculation of the uncertainties of the measurements of NOX and CO is not covered by this document.