At what location should you adapt to a larger vent when venting Category I furnaces?

The appropriate location to adapt to a larger vent when venting Category I furnaces is at the furnace connection. This is crucial because a larger vent diameter is necessary to ensure that the combustion gases generated by the furnace can be effectively carried away from the appliance, minimizing the risk of backdraft and improving the efficiency of gas venting.

Adapting at the furnace connection allows for a smooth transition from the smaller diameter of the furnace flue to the larger diameter venting system. This design helps maintain proper draft and ensures that all combustion products are efficiently removed from the home, preventing any potential hazards that may arise from improper venting.

Other locations such as the roof exit, along the horizontal run, or at the air intake are not optimal for making this adjustment. Venting systems are designed for optimal airflow, and making adjustments further along the venting pathway could compromise performance and safety, potentially increasing the likelihood of improper ventilation.