On a type L appliance vent with a single wall connector clearance of 9", what can the clearance to combustible material be reduced to when using 1/2" thick insulation board over a ventilated air space?

In the context of venting appliances, clearance to combustible materials is crucial for safety and compliance with building codes. For a type L appliance vent with a single wall connector specified to have a clearance of 9 inches, the introduction of insulation board can effectively reduce this required clearance when certain conditions are met.

Using 1/2" thick insulation board over a ventilated air space allows for a reduction in clearance because the insulation provides a barrier that protects combustibles from the heat emitted by the vent. Insulation minimizes the surface temperature increase on nearby combustibles, thereby making it safer to install the vent closer to these materials.

In this scenario, the clearance can be reduced to 5 inches above the vent and 3 inches to the sides and rear. This specific reduction adheres to guidelines that outline how insulation and proper installation can negate the need for standard clearances, ultimately allowing for safer and more flexible vent installation in confined or limited spaces. Ensuring that these minimum clearances are maintained helps to prevent potential fire hazards that could arise from inadequate spacing.

Understanding the use of insulation and air spaces is key for anyone working with vent systems, which is why this option is correct in this case.