Arkansas HVACR NewsMagazine November 2018

S tate, National, Chapter News Tech News

positive vent static pressure and with a vent gas temperature that usually avoids excessive condensate production in the vent. These appliances are direct sidewall vented without any additional apparatus. Positive pressure in the vent requires joints in the vent system to be sealed. Because these are 80 percent efficient sidewall vented appliances with combustion gases close to the dew point temperature, corrosion resistant materials must be used for the vent. And because condensate is possible, drains are typically incorporated to remove condensation before it can enter the heat exchanger. Category III appliances are typically used to solve installation problems where a vertical vent is not available. Category IV appliances operate with a positive vent static pressure and with a vent gas temperature that causes excessive condensate production in the vent. Same as with positive pressure Category III appliances, Category IV appliances must also have all joints sealed in the vent system. Category IV is intended to cover 90 percent plus efficient appliances. Category IV appliances are designed to dispose of combustion gas condensate as well as condensate formed within the

secondary heat exchanger of the appliance. Unlike with Category I appliances, there is no standard vent design procedure for Category II, III, and IV appliances. Every manufacturer of these type of appliances has to design a custom vent system specific to each model. Installers simply have to follow the manufacturer directions for these type appliances. For Category I appliances, there is a standard vent and connector design procedure. This procedure is in the International Fuel Gas Code , which is published by the International Code Council. Many in the industry refer to this procedure as the "vent tables." In addition, you will often find these vent tables reproduced in the literature of many manufacturers that produce venting products. Many factors affect the required vent and connector sizes for gas appliances. The appliance input Btuh rating, outlet diameter of the appliance, number of elbows, single or multi-story application, vent gas temperature, ambient air temperature, vent wall conductivity, vent connector type, vent thermal mass, vent pressurization (fan assisted or natural draft), vent height, and vent lateral length all affect vent design. The IFGC manual