Each furnace or heating unit in a building may have its own clearance requirements as established by the manufacturer. Furnace clearance requirements may also depend on your state or local building code. Speak to your local housing authority or building code agency for information about furnace requirements in your area.
Residential furnaces must meet local and state building codes and ordinance requirements. For example, the City of Mill Valley, California, requires that residential furnaces must be located at least 6 inches above the floor level, or grade. Furnaces must also have an unobstructed work space of at least 30 inches for the front and control sides of the furnace, as well as at least 12 inches on other sides. If the furnace is in a floodplain, the crawl area must be at least 12 inches between the ground and bottom of the furnace.
Furnace clearance requirements may also depend upon the age of the building and the nature of the space in which the furnace is installed. For example, in New York, boilers (also known as furnaces) installed before Match 31, 1965, must have "sufficient" clearance as necessary for proper operation. Those installed after March 31, 1965, must meet much more specific clearance requirements, while those installed in a room that had not been previously used as a boiler room must meet even more requirements.
Furnace manufacturers also establish minimum clearance requirements for individual units. For example, the Steffes 3100 requires zero clearance in the back, bottom and return and duct sides, 36 inches in the front, 4 inches on the left and 8 inches on the right and top side. Other furnaces built by the same company require different amounts of clearance, depending on the model.
Furnaces are also subject to other requirements. For example, the City of Mill Valley, California requires that any builder or installer must first obtain a permit to install a furnace replacement. All furnaces located in an attic or under a floor must have an accompanying electrical outlet and lighting fixture. Also, furnaces in an area where they may be subject to mechanical damage must be located behind an adequate barrier.
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