LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 7)

Mighty Therm Volume Water Heaters
Page 7
Method 1:
Two permanent openings, one commencing
within 12" (30 cm) of the top and one commencing
within 12" (30 cm) 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 directly, or 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" (30 cm) 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 ANSI Z223.1, or applicable
codes.
In Canada, Table 2 does not apply. Consult local
building and safety codes or, in absence of such
requirements, follow CAN/CGA B149.
NOTE: Check with louver manufacturers for
net free area of louvers. If screens or louvers are
installed, add 50 percent for each screen/louver to the
net free area Check all local codes applicable to
combustion air.
2.4.1 Outdoor Air Supply
When combustion air comes directly through an
outside wall, each opening must have a minimum free
area of at least one square inch for each 4,000 BTU/h
input of the total input rating of all appliances in the
enclosed area. (In Canada, refer to CGAB149.1 and .2.)
2.4.2 Indoor Air Supply
Confined and non-confined areas have different
requirements for installation. Consult the latest edition
of the National Gas Code for installation requirements.
2.4.3 Exhaust Fans or Vents
Any equipment which uses air or removes air
from the heater room can use up the combustion air
Required Net Free Opening Area
Directly from Outside
At Top At Bottom
Model in. 2 cm 2 in. 2 cm 2
175 44 284 44 284
250 63 406 63 406
325 82 529 82 529
400 100 645 100 645
Note: For screens or louvers, add 50%.
Table 2. Air Openings to Outside.
Figure 14. Indoor installation and venting.
Notes:
1.
The drafthood must sit directly on top of the heater
as shown and must not be altered in any manner.
2. An Underwriters' Laboratories listed vent cap is re-
quired to eliminate downdraft and allow the heater
to function properly.
3. Use approved roof fitting.
flue gases from inside the building (see Figure 14 and
Table 2 ). Laars does not recommend indoor
installations that do not provide combustion air from
outside the building.
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.