What is a typical vent stack temperature for a Category I furnace?

A typical vent stack temperature for a Category I furnace falls within the range of 350°F to 450°F. Category I appliances, which include conventional gas furnaces, operate with a positive vent pressure and are designed to discharge flue gases safely through a vertical vent stack. The temperatures in this range are necessary to ensure proper venting and to promote the efficient exhaust of combustion gases while minimizing the risk of condensation within the venting system.

When the vent stack operates within this temperature range, it helps maintain sufficient draft and prevents the buildup of corrosive condensates that can occur if the flue gases cool too much before exiting the vent. Maintaining higher temperatures in the vent stack ensures that the combustion products are carried away effectively, thereby improving the safety and efficiency of the furnace operation.

In contrast, the other temperature ranges mentioned would either indicate inefficient operation or conditions that could lead to condensation and potential damage to the venting system or the appliance itself.