Instruction manual

Atmospheric Gas Page 9
SECTION III: PRE-INSTALLATION (cont.)
CONFINED SPACE (CONT.)
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
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 “Natural” column. 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 by download from www.bockwaterheaters.com. Note: Do not reduce vent size more
than one size smaller than the vent connector supplied with the heater. If vent size must be
reduced one size, use full size vent connectors on the vent hood and reduce vent size as far
from the water heater as practical. B vent, L vent or multi-fuel venting may be used. Vent
tables supplied by the vent manufacturer may also be used in sizing the vent system.
Venting system must be capable of producing –0.02" WC (inches of water column) draft
minimum. If draft of –0.02" WC cannot be produced with an existing vent system, a draft
inducer may be required. Installations common vented with large vent hood equipped
appliances such as heating boilers may require vent dampers on the heating boiler connectors
for proper vent operation during no-heating season.
Check the building for items that can cause severe negative pressure problems such as large
exhaust fans. If these devices are installed in the same building check for their effect on draft
and combustion. All fuel burning appliances must be isolated from the effects of these devices
to operate properly. Failure to address this issue will result in unsafe operation and shorten
appliance life spans.
Your Bock water heater may also be operated with a power venter. The power venter must be
properly sized and adjusted to provide proper draft. Power venter wiring must turn on the
power venter on a call for heat and must prove venter operation before allowing the burner to
start. Refer to the power venter instructions for proper wiring and adjustment procedures.