will build to the point that a downdraft can occur in the fur nace vent pipe or chimney. As a result, combustion gases enter the living space creating a potentially dangerous situ ation.
In the absence of local codes concerning air for combus- tion and ventilation, use the guidelines and procedures in this section to install ML193UH furnaces to ensure efficient and safe operation. You must consider combustion air needs and requirements for exhaust vents and gas piping. A portion of this information has been reprinted with per mission from the National Fuel Gas Code (ANSI- Z223.1/NFPA 54). This reprinted material is not the com plete and official position of the ANSI on the referenced subject, which is represented only by the standard in its en tirety.
In Canada, refer to the CSA B149 installation codes.
CAUTION
Do not install the furnace in a corrosive or contami nated atmosphere. Meet all combustion and ventila tion air requirements, as well as all local codes.
All gas‐fired appliances require air for the combustion pro cess. If sufficient combustion air is not available, the fur nace or other appliance will operate inefficiently and un safely. Enough air must be provided to meet the needs of all
In addition to providing combustion air, fresh outdoor air di lutes contaminants in the indoor air. These contaminants may include bleaches, adhesives, detergents, solvents and other contaminants which can corrode furnace compo
infiltration. If the furnace is located in a building of tight construction with weather stripping and caulking around the windows and doors, follow the procedures in the Air from Outside section.
Confined Space
A confined space is an area with a volume less than 50 cu bic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the
When the furnace is installed so that supply ducts carry air circulated by the furnace to areas outside the space con taining the furnace, the return air must be handled by ducts which are sealed to the furnace casing and which terminate outside the space containing the furnace. This is especially important when the furnace is mounted on a platform in a confined space such as a closet or small equipment room. Even a small leak around the base of the unit at the platform or at the return air duct connection can cause a potentially dangerous negative pressure condition. Air for combustion and ventilation can be brought into the confined space ei ther from inside the building or from outside.
Air from Inside
If the confined space that houses the furnace adjoins a space categorized as unconfined, air can be brought in by providing two permanent openings between the two spaces. Each opening must have a minimum free area of 1 square inch (645 mm2) per 1,000 Btu (.29 kW) per hour of total input rating of all
mm)of the top of the enclosure and one opening within 12 inches (305 mm) of the bottom. See figure 4.
EQUIPMENT IN CONFINED SPACE - ALL AIR FROM INSIDE
nents.
The requirements for providing air for combustion and ven tilation depend largely on whether the furnace is installed in an unconfined or a confined space.
Unconfined Space
An unconfined space is an area such as a basement or large equipment room with a volume greater than 50 cubic feet (1.42 m3) per 1,000 Btu (.29 kW) per hour of the com bined input rating of all appliances installed in that space.
ROOF TERMINATED EXHAUST PIPE
SIDE WALL
TERMINATED EXHAUST PIPE (ALTERNATE LOCATION)
ML193UH
OPENINGS
(To Adjacent
Unconfined
Space)
This space also includes adjacent rooms which are not separated by a door. Though an area may appear to be un confined, it might be necessary to bring in outdoor air for combustion if the structure does not provide enough air by
NOTE - Each opening shall have a free area of at least one square inch per 1,000 Btu (645mm2 per .29kW) per hour of the total input rating of all equipment in the enclosure, but not less than 100 square inches (64516mm.2).
FIGURE 4
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