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STEP 4. Compare the total Btu the area can support (from Step 2) to the total Btu in the area the heater will be installed
(from Step 3). If the total from Step 2 is larger this is considered an unconfined space, if Btu total from Step 3 is larger this
is considered a confined space and provisions must be made for additional combustion and ventilation air. EXAMPLE:
Btu area can support is 56,250, total Btu in area is 106,000 – this would be a confined space.
NOTE: A third construction class is one with unusually tight construction, defined as, construction where: (A) Walls
and ceilings exposed to the outside atmosphere have a continuous water vapor retarder with a rating of 1 per (6x10-11 Kg
per pa-sec-m²) or less with openings gasketed or sealed, and, (B) Weatherstripping has been added enable windows and
doors, and , (C) Caulking or sealants are applied to areas such as joints around window and door frames, between sole
plates and floors, between wall ceiling joints, between wall panels, at penetration for plumbing, electrical, and gas lines,
and at other openings.
“WARNING: If the area in which the heater may be operated is smaller than that defined as an unconfined space, or if the
building is of unusually tight construction, provide adequate combustion and ventilation air by one of the methods
described in the National Fuel Gas Code, ANSI Z223.1, Section 5.3 or applicable local codes.” Examples would be to
provide two permanent openings either to an adjoining room, or to the outside. See the National Fuel Gas Code for
details. See Figure 9 & Figure 10 below.
FRESH AIR FOR COMBUSTION, VENTILATION AND HEAT DISTRIBUTION - CONT’D.
INSTALLATION
Installation and service must be performed by a qualified installer, service agency or the gas supplier.
LOCATION
1) For most efficient performance, locate heater as centrally as possible in the area to be heated.
2) Do not install heater in a closet, alcove or small hallway where the heater could be isolated from the space to be
heated and adequate combustion air by closing a door.
Page 5
Chimney or gas vent
Opening
Opening
Equipment located in confined
spaces; all air from inside the
building. See 5.3.3(a).
Furnace
Water
Heater
FIGURE 9
Chimney or gas vent
Water
Heater
Furnace
Ventilation louvers
(each end of attic)
Outlet Air
Inlet Air
Alternate
air inlet
Ventilation louvers for
unheated crawl space
Equipment located in confined spaces; all air from
outdoors - inlet air from ventilated crawl space and
outlet air to ventilated attic. See 5.3.3(b).
FIGURE 10