Combustion And Ventilation Air; Unconfined Space - Bock Water heaters ezFIT Installation And Operation Instruction Manual

COMBUSTION AND VENTILATION AIR

The water heater must be installed in a location with an adequate air supply for combustion,
ventilation and draft control. Unsafe levels of carbon monoxide (CO), condensation and soot-
ing may result if the room does not have an adequate air supply. See "National Fuel Gas Code
(NFPA 54)" or the discussions of "Unconfined Space" and "Confined Space" below. Poor venti-
lation will also result in hot spots around the heater. Temperatures over 90° near the water
heater generally indicate a lack of ventilation.

UNCONFINED SPACE

Unconfined space is defined by NFPA 54 as a space with a volume greater than 50 cubic feet
(during typical use) per 1000 BTUH of the total combined input of all fuel burning appliances
in the space. Rooms leading directly to the installation space through doors that cannot be
closed can be considered part of the space. Exception: Buildings with full vapor barriers, tight
doors and windows or air infiltration rates of less than 0.35 air changes per hour will be consid-
ered a confined space and require additional air supplies.
CONFINED SPACE
Confined space is defined by NFPA 54 as a space with a volume less than 50 cubic feet (during
typical use) per 1000 BTUH of the total combined input of all fuel burning appliances in the
space. Buildings or rooms of unusually tight construction are also considered a confined
space. See "Unconfined Space: Exception".
When installing fuel burning appliances in a confined space, air must be supplied to that
space from either inside or outside of the building as conditions allow.
A. Inside Air Supply: A confined space shall be provided with two permanent openings; one
within 12 inches of the top and one within 12 inches of the bottom of the enclosure. These
openings shall lead directly to room(s) of sufficient volume so that the combined volume of
all the space meets the criteria for unconfined space. Each opening shall have a minimum free
area of 1 square inch per 1000 Btu/hr of the combined total input of all fuel burning appli-
ances in the space. Each opening shall have an area of not less than 100 square inches or a
minimum dimension of not less than 3 inches.
B. Outside Air Supply: Confined spaces shall be provided with two permanent openings; one
within 12 inches of the top and one within 12 inches of the bottom of the enclosure. These
openings shall communicate directly, or by ducts, with the outdoors or spaces that
communicate with the outdoors.
1.) Leading directly to the outside or through vertical ducts: Each opening shall have a
minimum free area of one square inch per 4000 Btu/hr of total input rating of all equipment
in the enclosure.
2.) Leading to outside through horizontal ducts: Each opening shall have a minimum free
area of one square inch per 2000 Btu/hr of total input rating of all equipment in the enclosure.
Note: All ducts shall have the same cross sectional area as the free area of each opening to
which they connect. The minimum dimensions of all ducts shall not be less than three inches.
Powered combustion air supplies are also commercially available and may be used.
LOUVERS & GRILLES
In calculating the free area of an opening, consideration must be given to the blocking effects
of louvers or grilles protecting the opening. Any screens used must be no finer than
mesh. If the free area of a louver or grille is known, this should be used in calculating the size
of opening required. If free area is unknown, it may be assumed that wood louvers will have
20 to 25% free area and metal louvers and grilles will have 60 to 75% free area. Louvers and
grilles should be fixed in the open position or interlocked with the equipment so that they
open automatically during equipment operation.
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