The new venting guidelines adopted by the National Fuel Gas Code resolve the majority of venting problems associated with the recent introduction of fan-assisted gas appliances. For retrofit installations that fall outside the scope of the new guidelines, however, additional analysis is required to ensure proper venting action and trouble-free operation. The new venting guidelines can help provide guidance as to what to look for in the analysis. Field experience is also important in guiding the analysis. The VENT-II computer program, which was used to generate the new vent sizing guidelines, is also an appropriate tool for analysing unique venting situations. Presents an example of the type of analysis required.

KEYWORDS: computer programs, regulations, gas installations, modernising, vents, fans, gas fired boilers, boilers, gas, appliances, sizing, combustion gases, flue gases.