12
cross-sectional area should be at least 1in.² of free
area per 10,000 BTUH (222 mm² per kW) of total
input rating of all equipment in the room, when the
opening is communicating with the outdoors
through horizontal duct(s). Damage to the equip-
ment due to inadequate ventilation of the space is
not a warrantable failure.
9. In cold climates, and to mitigate potential freeze-
up, Raypak highly recommends the installation of
a motorized sealed damper to prevent the circula-
tion of cold air through the heater during the
non-operating hours.
TruSeal™ Combustion Air
In addition to the nine previous steps, combustion air
may be ducted directly to the heater by using PVC,
CPVC or sealed single-wall galvanized ducting. The
duct will attach directly to the field installed air collar
located on the rear of the heater, using three or four
sheet metal screws (not supplied) equally positioned
around the circumference of the duct. The screws and
duct connection point should be sealed with RTV (not
supplied). TruSeal is generally used when damaging
contaminants are present in the mechanical room. All
ducting
MUST
be self-supported.
Conventional Combustion Air
Supply
U.S. Installations
All Air from Inside the Building
The confined space shall be provided with
TWO
per-
manent openings communicating directly with an
additional room(s) of sufficient volume so that the com-
bined volume of all spaces meets the criteria for a
room large in comparison (NFGC). The total input of all
gas utilization equipment installed in the combined
space shall be considered in making this determina-
tion.
Each opening
shall have a minimum free area of
1 in.
2
per 1,000 BTUH (2,225 mm
2
per kW) of the total
input rating of all gas utilization equipment in the con-
fined space, but not less than 100 in.
2
(645 cm
2
). One
opening shall commence within 12 in. (305 mm) of the
top, and one opening shall commence within 12 in.
(305 mm) of the bottom of the enclosure. The mini-
mum dimension of air openings shall be not less than
3 in. (76 mm) in any direction.
All Air from Outdoors
The confined space shall communicate with the out-
doors in accordance with one of the methods below.
The minimum dimension of air openings shall not be
less than 3 in. (76 mm) in any direction. Where ducts
are used, they shall be of the same cross-sectional
area as the net free area of the openings to which they
connect.
1.
Two permanent openings
, one commencing
within 12 in. (305 mm) of the top, and one com-
mencing within 12 in. (305 mm) of the bottom of
the enclosure, shall be provided. The openings
shall communicate directly, or by ducts, with the
outdoors or spaces (crawl or attic) that freely com-
municate with the outdoors.
a. Where directly communicating with the out-
doors or where communicating to the
outdoors through vertical ducts,
each open-
ing
shall have a minimum free area of 1 in.
2
per 4,000 BTUH (550 mm
2
per kW) of total
input rating of all equipment in the enclosure.
b. Where communicating with the outdoors
through horizontal ducts, each opening shall
have a minimum free area of 1 in.
2
per 2,000
BTUH (1,100 mm
2
per kW) of total input rat-
ing of all equipment in the enclosure.
2.
One permanent opening
, commencing within 12
in. (305 mm) of the top of the enclosure, shall be
permitted where the equipment has clearances of
at least 1 in. (25 mm) from the sides and back and
6 in. (152 mm) from the front of the appliance. The
opening shall directly communicate with the out-
doors or shall communicate through a vertical or
horizontal duct to the outdoors or spaces that
freely communicate with the outdoors, and shall
have a minimum free area of:
a. 1 in.
2
per 3,000 BTUH (740 mm
2
per kW) of
the total input rating of all equipment located in
the enclosure, and
b. Not less than the sum of the areas of all vent
connectors in the confined space.
CAUTION:
Use TruSeal combustion air if
damaging airborne contaminants are or may be
present in the heater area. See the Appendix of this
manual regarding air contamination.
WARNING:
Do not use the “one permanent
opening” method if the equipment room is under
negative pressure conditions.
