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The minimum temperature above the flue gas dew point for a category 1 venting system is indeed 140°F. This is essential to prevent condensation of flue gases within the venting system. When the flue gases cool down and reach the dew point, the water vapor in the gases can condense, leading to potential issues such as corrosion of the venting materials and degradation of efficiency in gas appliances.

In category 1 venting systems, which are typically used for natural draft appliances, maintaining this minimum temperature is crucial. Operating above the dew point ensures that any moisture remains in vapor form, thereby protecting the system from the adverse effects of condensation. This temperature is carefully specified in codes and best practices to ensure safety and longevity of the venting systems associated with gas appliances.