Section 6.1.1/Warm Air Heating Equipment Installation
NFPA 90B Section 6.1 covers furnace installation clearances, return air restrictions, and combustion air for residential heating.
Warm air furnaces must be installed with minimum clearances to combustible materials as specified by the manufacturer's listing and the equipment label. The supply plenum must be constructed of galvanized steel or equivalent noncombustible material for at least 3 feet from the furnace. Return air openings must not be located in a garage, storage closet, or space containing fuel-fired equipment (to prevent drawing combustion products or flammable vapors into the return air system). The furnace must have adequate combustion air per Section 5.1.
Why this section exists
Residential furnaces generate heat surfaces that can ignite nearby combustible materials. The clearance requirements prevent ignition of wood framing, insulation, and stored materials near the furnace. The return air restrictions prevent the HVAC system from distributing carbon monoxide from a water heater or furnace malfunction, or flammable vapors from a garage, throughout the occupied spaces. These are among the most common sources of residential fire and carbon monoxide incidents.
What plan reviewers look for
Plan reviewers check the mechanical plan for furnace clearances to surrounding combustible construction. They verify the supply plenum material (noncombustible for the first 3 feet). They check that return air grilles are not located in garages, mechanical closets with fuel-fired equipment, or storage spaces. They verify combustion air provisions for the furnace location.