appliances 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 equip-
ment 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
1
⁄
4
inch
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.
VENTING
The water heater shall be located as close to the chimney as practical. Long lateral runs will
result in intermittent combustion problems and unsafe operating conditions. Total vent
height should be a minimum of 6 feet. Shorter vent heights could result in unstable draft and
nuisance lock outs.
The venting system should be sized according to National Fuel Gas Code: NFPA 54/ANSI
Z223.1 (most recent edition) using the “Fan Min, Max” columns. If you do not have a copy of
this code one can be obtained at www.NFPA.org for a nominal fee. Copies of the NFPA venting
tables are also reprinted in the Bock Engineering Manual available from your Bock Represen-
tative or download from www.bockwaterheaters.com.
Note:
Do not reduce vent size more
than one size smaller than the vent connector supplied with the heater. B vent, L vent or
multi-fuel chimneys may be used. Single wall vent connectors may also be used.
When connecting to an existing vent system, examine the piping and system for condition.
Replace any sections that show signs of significant corrosion or have become perforated. Also
verify that the system is of the correct type and sized properly for the water heater and any
other appliances that are connected to it. Correct any discrepancies found between the exist-
ing system and current NFPA 54 code.
Draft must be controlled with a barometric damper or draft regulator approved for gas appli-
ances, normally supplied with each complete Bock Water Heater.
(This device differs from a
vent/flue damper in that it precisely regulates the amount of room air entering the vent to control
draft. A vent/flue damper shuts off the vent during stand by periods to reduce losses and has no
effect of draft.)
The draft regulator may be installed in a tee on top of the water heater and
must be adjusted while the water is running to regulate draft to a minimum of –0.02 inches
water column (WC) and a maximum of –0.05" WC. Draft over the fire should be slightly nega-
tive. Draft is normally adjusted by hanging washers (supplied with the draft regulator) on the
draft regulator chain. Follow the instruction supplied with the draft regulator for proper loca-
tion and draft adjustment procedures.
Note:
Failure to install the barometric damper or adjust
draft properly will result in unsafe operating conditions and nuisance burner lock outs.
Power Gas
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