Definition from 2022 NYC Mechanical Code:
FLOOR FURNACE.A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space.
Fan type. A floor furnace equipped with a fan that provides the primary means for circulating air.
Gravity type. A floor furnace depending primarily on circulation of air by gravity. This classification shall also include floor furnaces equipped with booster-type fans that do not materially restrict free circulation of air by gravity flow when such fans are not in operation.
Floor Furnace Installation Requirements from 2002 NYC Mechanical Code
Section 910 Floor Furnaces
910.1 General
Floor furnaces shall be installed in accordance with their listing and the manufacturer's instructions. Oil-fired furnaces shall be tested in accordance with UL 729. Unvented floor furnaces are prohibited.
910.2 Placement
Floor furnaces shall not be installed in any corridor, in the floor of any aisle or passageway of any auditorium, public hall, place of assembly, or in any egress element from any such room or space.
With the exception of wall register models, a floor furnace shall not be placed closer than 6 inches (152.4 mm) to the nearest wall, and wall register models shall not be placed closer than 6 inches (152.4 mm) to a corner.
The furnace shall be placed such that a drapery or similar combustible object will not be nearer than 12 inches (304.8 mm) to any portion of the register of the furnace. Floor furnaces shall not be installed in concrete floor construction built on grade. The controlling thermostat for a floor furnace shall be located within the same room or space as the floor furnace or shall be located in an adjacent room or space that is permanently open to the room or space containing the floor furnace. Floor furnaces shall be located so as to be accessible. Floor furnaces shall be installed only in floors of noncombustible construction having at least a 2-hour fire rating, except as where required for one- and two-family dwellings.
910.3 Bracing
The floor around the furnace shall be braced and headed with a support framework design in accordance with the New York City Building Code.
910.4 Clearance
The lowest portion of the floor furnace shall have not less than a 6-inch (152.4 mm) clearance from the grade level; except where the lower 6-inch (152.4 mm) portion of the floor furnace is sealed by the manufacturer to prevent entrance of water, the minimum clearance shall be reduced to not less than 2 inches (50.8 mm). Where these clearances are not present, the ground below and to the sides shall be excavated to form a pit under the furnace so that the required clearance is provided beneath the lowest portion of the furnace. A 12-inch (304.8 mm) minimum clearance shall be provided on all sides except the control side, which shall have an 18-inch (457.2 mm) minimum clearance.
910.5 Enclosures
Enclosures of floor furnaces shall be constructed entirely of noncombustible materials with a fire-resistance rating of at least 1 hour and shall be provided with adequate outdoor air to ensure proper combustion. The enclosure shall be provided with adequate means of access for servicing the furnace.
910.6 Duct Temperature
The outlet duct temperature of warm air heating furnaces shall not be greater than 250°F (121.1°C).
910.7 One- And Two- Family Dwellings
Floor furnace enclosures shall be constructed of noncombustible materials with a fire-resistance rating of at least 1 hour. Means shall be provided for supporting the furnace when the grille is removed. Clearances shall be provided as per NFPA 54.
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