What must ducts connecting to a furnace maintain concerning combustibles?

Ducts connecting to a furnace must maintain a specific clearance from combustibles to ensure safety and prevent fire hazards. This clearance is critical because ducts can heat up significantly when used for distributing conditioned air or during the operation of the furnace.

If ducts are too close to combustible materials, such as framing, insulation, or other flammable items, they can transfer excessive heat, potentially causing those materials to ignite. The code specifies these clearances to minimize the risk of thermal contact and to ensure safe operation.

Proper adherence to clearance requirements protects both the integrity of the duct system and the overall safety of the building's occupants. It's essential for HVAC professionals to understand and apply these standards according to the North Carolina Mechanical Code to ensure compliance and safety.