HTP CG N65 Series, Installation, Start-Up, Maintenance, Parts, Warranty

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LP-436 Rev. 5.20.15
9
Figure 4 - Confined Space - Communicating Directly with
Outdoors
2) When communicating with the outdoors through vertical
ducts, each opening shall have a minimum free area of one (1)
square inch per 4,000 BTU/H (5.5 cm
2
/kW) of the total input
rating of all gas appliances in the enclosure. See Figure 5.
Figure 5 - Confined Space - Communicating Outdoors through
Vertical Ducts
3) When communicating with the outdoors through horizontal
ducts, each opening shall have a minimum free area of one (1)
square inch per 2,000 BTU/H (11 cm
2
/kW) of the total input
rating of all gas appliances in the enclosure. See Figure 6.
Figure 6 - Confined Space - Communicating Outdoors through
Horizontal Ducts
In Canada (refer to CAN/CSA B149.1)
a. All Air From Inside the Building
The confined space shall be provided with one opening of one
(1) square inch per 1,000 BTU/H (22 cm
2
/kW) communicating
directly with one or more rooms of sufficient volume, so that
the combined volume of all spaces meets the criteria for an
unconfined space for all the appliances installed in that confined
space. See Figure 7.
When ducts are used, they shall be of the same cross-sectional
area as the free area of the openings to which they connect. The
minimum short side dimension of rectangular air ducts shall not
be less than three (3) inches (7.6 cm).
b. All Air From Outdoors
An air supply shall be provided with one opening that
communicates directly with the outdoors by means of a duct.
This duct shall be sized according to CAN/CSA B149.1 and
terminate within one (1) foot above and within two (2) feet
horizontally from the burner level of the appliance having the
largest input. See Figure 8.
Figure 7 - Confined Space - All Air from Inside Building
Figure 8 - Confined Space - All Air from Outdoors through Duct
3. Louvers and Grilles
In calculating free area for ventilation and combustion air supply
openings, consideration must be given to the blocking effect
of louvers, grilles, or screens protecting the openings. Screens
must not be smaller than ¼” (6.4 mm) mesh. If the free area
through a particular design of louver or grille is known, it should
be used in calculating the size of opening required to provide the
free area specified. If the design and free area is not known, it