Unconfined Space; Confined Space; Fresh Air Openings For Confined Spaces; Outdoor Air Through One And Two Openings - A.O. Smith BTX-80 SERIES 100 Instruction Manual

Such a condition often will result in a yellow, luminous burner
flame, causing sooting of the combustion chamber, burners and
flue tubes and creates a risk of asphyxiation.
Do not install the water heater in a confined space unless an
adequate supply of air for combustion and ventilation is brought in
to that space using the methods described in the Confined Space
section that follows.
Never obstruct the flow of ventilation air. If you have any doubts or
questions at all, call your gas supplier. Failure to provide the proper
amount of combustion air can result in a fire or explosion and cause
property damage, serious bodily injury or death.

unconfIned space

An Unconfined Space is one whose volume is not less than 50 cubic
feet per 1,000 Btu/hr (4.8 cubic meters per kW) of the total input
rating of all appliances installed in the space. Rooms communicating
directly with the space, in which the appliances are installed, through
openings not furnished with doors, are considered a part of the
unconfined space.
Makeup air requirements for the operation of exhaust fans, kitchen
ventilation systems, clothes dryers and fireplaces shall also be
considered in determining the adequacy of a space to provide
combustion, ventilation and dilution air.
unusuallY tIGht constructIon
In unconfined spaces in buildings, infiltration may be adequate to
provide air for combustion, ventilation and dilution of flue gases.
However, in buildings of unusually tight construction (for example,
weather stripping, heavily insulated, caulked, vapor barrier, etc.)
additional air must be provided using the methods described in the
Confined Space section that follows.

confIned space

A Confined Space is one whose volume is less than 50 cubic feet
per 1,000 Btu/hr (4.8 cubic meters per kW) of the total input rating
of all appliances installed in the space.
Openings must be installed to provide fresh air for combustion,
ventilation and dilution in confined spaces. The required size for the
openings is dependent on the method used to provide fresh air to
the confined space and the total Btu/hr input rating of all appliances
installed in the space.
dIrect vent applIances
Appliances installed in a Direct Vent configuration that derive all
air for combustion from the outdoor atmosphere through sealed
intake air piping are not factored in the total appliance input Btu/hr
calculations used to determine the size of openings providing fresh
air into confined spaces.
eXhaust fans
Where exhaust fans are installed, additional air shall be provided
to replace the exhausted air. When an exhaust fan is installed in
the same space with a water heater, sufficient openings to provide
fresh air must be provided that accommodate the requirements for
all appliances in the room and the exhaust fan. Undersized openings
will cause air to be drawn into the room through the water heater's
vent system causing poor combustion. Sooting, serious damage to
the water heater and the risk of fire or explosion may result. It can
also create a risk of asphyxiation.
louvers and GrIlles
The free areas of fresh air openings in instructions that follow do not take
in to account presence of louvers, grilles or screens in openings.
The required size of openings for combustion, ventilation and dilution
air shall be based on the "net free area" of each opening. Where the
free area through a design of louver or grille or screen is known, it
shall be used in calculating the size of opening required to provide the
free area specified. Where the louver and grille design and free area
are not known, it shall be assumed that wood louvers will have 25%
free area and metal louvers and grilles will have 75% free area. Non
motorized louvers and grilles shall be fixed in the open position.

fresh aIr openInGs for confIned spaces

The following instructions shall be used to calculate the size, number
and placement of openings providing fresh air for combustion,
ventilation and dilution in confined spaces. The illustrations shown in
this section of the manual are a reference for the openings that provide
fresh air into confined spaces only. Do not refer to these illustrations
for the purpose of vent installation. See Installation of Vent System on
pages 19-26 for complete venting installation instructions.
outdoor aIr throuGh two openInGs
The confined space shall be provided with two permanent
openings, one commencing within 12 inches (300 mm) of the top
and one commencing within 12 inches (300 mm) of the bottom
of the enclosure. The openings shall communicate directly with
the outdoors. See Figure 6.
Each opening shall have a minimum free area of 1 square inch
per 4,000 Btu/hr (550 mm
of all appliances installed in the enclosure. Each opening shall
not be less than 100 square inches (645 cm
outdoor aIr throuGh one openInG
Alternatively a single permanent opening, commencing within 12
inches (300 mm) of the top of the enclosure, shall be provided. See
13
fIGure 6.
per kW) of the aggregate input rating
2
).
2
fIGure 7.