What is the minimum clearance requirement between clearance reduction systems and combustible walls for systems using ventilated airspace?

The minimum clearance requirement between clearance reduction systems and combustible walls for systems utilizing ventilated airspace is established to ensure safety and compliance with fire regulations. In this case, the correct answer is a 1-inch clearance.

This clearance is important because it allows for adequate airflow and minimizes the risk of heat transfer to combustible materials. Ventilated airspace acts as a barrier that can help cool surfaces and prevent ignition, so the specified clearance ensures that there is enough space for ventilation to be effective. Maintaining this distance is also essential for preventing the accumulation of heat and potential fire hazards that could arise from being too close to combustible surfaces.

The other options specify larger clearances, which are not required in this scenario where ventilated airspace is in use. This distinction is critical for proper installation and adherence to safety codes in mechanical systems.