What is an acceptable method to reduce clearance by 3" for a vent connector to combustible material?

The correct answer involves using 0.25" (6 mm) insulating millboard spaced out by 1" (25 mm). This method is acceptable because the insulating millboard possesses the ability to significantly reduce the temperature of the vent connector, making it safer in proximity to combustible materials. Insulating millboard is specifically designed to offer thermal protection, which helps to maintain a safe operating temperature and prevents the risk of combustion.

The requirement of spacing the millboard out by 1" (25 mm) contributes further to safety, as this distance enhances airflow and dissipates heat more effectively, thereby reducing the chances of heat transfer to the combustible materials beyond the insulating barrier. This ensures that even if the millboard reaches elevated temperatures, the combustible materials remain at a safe temperature, minimizing any fire hazard.

Other methods mentioned either do not provide adequate material properties for insulation or do not offer sufficient spacing, thus failing to meet the necessary safety standards when dealing with vent connectors and combustible materials. The 0.25" (6 mm) thickness is also suitably substantial to ensure effective thermal insulation in accordance with TSSA regulations.