LAARS Rheos RHCV - Install and Operating Manual - Manual (Page 7)

Rheos Boiler and Water Heater Page 7
SECTION 2.
Venting and Combustion Air
2.1 Combustion Air
Rheos boilers and water heaters must have
provisions for combustion and ventilation air in
accordance with section 5.3, Air for Combustion and
Ventilation, of the National Fuel Gas Code, ANSI
Z223.1, or Sections 7.2, 7.3 or 7.4 of CSA B149.1,
Installation Codes, and applicable provisions of the
local building codes.
A Rheos unit can take combustion air from the
space in which it is installed, or the combustion air can
be ducted directly to the unit. Ventilation air must be
provided in either case.
2.1.1 Combustion Air From Room
In the United States, the most common
requirements specify that the space shall communicate
with the outdoors in accordance with method 1 or 2,
which follow. Where ducts are used, they shall be of
the same cross-sectional area as the free area of the
openings to which they connect.
Method 1: Two permanent openings, one
commencing within 12" (300mm) of the top and one
commencing within 12" (300mm) of the bottom, of
the enclosure shall be provided. The openings shall
communicate directly, or by ducts, with the outdoors
or spaces that freely communicate with the outdoors.
When directly communicating with the outdoors, or
when communicating to the outdoors through vertical
ducts, each opening shall have a minimum free area
of 1 square inch per 4000 Btu/hr (550 square mm/kW)
of total input rating of all equipment in the enclosure.
When communicating to the outdoors through
horizontal ducts, each opening shall have a minimum
free area of not less than 1 square inch per 2000 Btu/hr
(1100 square mm/kW) of total input rating of all
equipment in the enclosure.
Method 2: One permanent opening, commencing
within 12" (300mm) of the top of the enclosure, shall
be permitted. The opening shall directly communicate
with the outdoors or shall communicate through a
vertical or horizontal duct to the outdoors or spaces
that directly communicate with the outdoors and shall
have a minimum free area of 1 square inch per 3000
Btu/hr (734 square mm/kW) of the total input rating of
all equipment located in the enclosure. This opening
must not be less than the sum of the areas of all vent
connectors in the confined space.
Other methods of introducing combustion and
ventilation air are acceptable, providing they conform
to the requirements in the applicable codes listed
above.
In Canada, consult local building and safety
codes or, in absence of such requirements, follow
CAN/CGA B149.
2.1.2 Intake Combustion Air
The combustion air can be taken through the
wall, or through the roof. When taken from the wall, it
must be taken from out-of-doors by means of the Laars
horizontal wall terminal, shown in Table 4. See Table 3
to select the appropriate diameter air pipe. When taken
from the roof, a field-supplied rain cap or an elbow
arrangement must be used to prevent entry of rain
water (see Figure 2).
Use single-wall galvanized pipe for the
combustion air intake (see Table 5), sized per Section
1.8. Route the intake to the heater as directly as
possible. Seal all joints with tape. Provide adequate
hangers. The unit must not support the weight of the
combustion air intake pipe. Maximum linear pipe
length allowed is 50 feet (15.2m). Up to five elbows
can be used with the 50 feet of pipe. Subtract 10
allowable linear feet for every additional elbow used.
Figure 2. Combustion Air and Vent Through Roof.
Model Intake Exhaust Intake Exhaust
Size Size Maximum Run Maximum Run
1200 6" (15 cm) dia. 6" (15 cm) dia. 50 linear feet with 5 elbows 50 linear feet with 5 elbows
1600 8" (20 cm) dia. 6" (15 cm) dia. 50 linear feet with 5 elbows 50 linear feet with 5 elbows
2000 8" (20 cm) dia. 7" (18 cm) dia. 50 linear feet with 5 elbows 50 linear feet with 5 elbows
2400 8" (20 cm) dia. 10" (25 cm) dia. 50 linear feet with 5 elbows 50 linear feet with 5 elbows
Table 3. Vent / Air Pipe Sizes.