Section 4.1.1/Warm Air Heating System Installation
NFPA 90B Section 4.1 covers installation requirements for warm air heating systems in one and two-family dwellings.
Warm air furnaces and air conditioning equipment must be installed with the required clearances from combustible materials as specified by the manufacturer's listing and the equipment nameplate. Ducts must be constructed of metal or other approved materials. Supply ducts within 3 feet of the furnace plenum must be metal. Return air must not be taken from bathrooms, kitchens, garages, mechanical rooms, or any room where combustion equipment is located.
Why this section exists
Residential warm air heating systems are the most common HVAC system type in the United States. The installation requirements prevent fire hazards from equipment installed too close to combustible materials, from combustible duct materials near hot plenums, and from return air that draws hazardous contaminants (garage fumes, bathroom moisture, cooking grease) into the duct system and distributes them throughout the dwelling.
What plan reviewers look for
Plan reviewers check furnace locations for clearances from combustible walls, floors, and ceilings. They verify that duct materials near the furnace are metal. They check that return air grilles are not located in garages, bathrooms, kitchens, or rooms containing combustion equipment. They also verify that the furnace is accessible for service and filter replacement.
Common violations
Related NFPA 90B requirements
Section 5.1 covers duct construction requirements. NFPA 90A covers the equivalent requirements for commercial and larger buildings. IMC Section 306 covers equipment clearance requirements in the International Mechanical Code.