Demand Duo
™
R
-
Series Installation and Operation Manual
23
When communicating
indirectly
with the
outdoors through vertical ducts, each opening
shall have a minimum free area of 1 in
2
/4000
Btu/hr (550 mm
2
/kW) of total input rating of all
appliances in the confined space. Combustion
air to the appliance can be provided from a well
ventilated attic or crawl space.
Outdoor air can be provided to a confined space
through two permanent openings, one
commencing within 12 in. (300mm) of the top and
one commencing within 12 in. (300mm) of the
bottom, of the confined space. The openings shall
communicate to the outside by one of two ways:
1.
Directly through horizontal ducts
2.
Indirectly through vertical ducts
When communicating
directly
with the
outdoors through horizontal ducts, each
opening shall have a minimum free area of 1
in
2
/2000 Btu/hr (1100 mm
2
/kW) of total input
rating of all appliances in the confined space.
Figure 14: Directly through horizontal ducts
Figure 15: Indirectly through vertical ducts
NOTE
If ducts are used, the cross sectional area of
the duct must be greater than or equal to the
required free area of the openings to which
they are connected.
When using air from other room(s) in the
building, the total volume of the room(s) must be
of adequate volume (greater than 50 cubic feet
per 1000 Btu/hr). Regardless of the calculated
free area, the combustion air opening should
never be less than 100 square inches each.
Figure 16
