Odyssey
│
Installation and Operation Instructions - Natural Draft
CT80-250
16
Sizing Combustion Air Openings
The following sections detail the three (3) methods for determining the minimum opening size and location
required for providing combustion air:
1.
Indoor Air - Opening Sizes: Older buildings typically have sufficient ventilation due to air leakage around
single pane windows, poorly weather-stripped doors, and non-existent vapour barrier. Indoor air can be used
to supply combustion air to the boiler area if the air infiltration rate is adequate, i.e. greater than 0.4 ACH (air
changes per hour) or when the boiler area and communicating spaces have a minimum volume of 50 cubic ft
per 1000 Btu/hr. If the air infiltration rate is known to be less that 0.4 ACH, refer to the Installation Code for
Oil-Burning Equipment for further guidance.
a.
Combined spaces on the same story
minimum free area of openings = 1 in.
2
/1000 Btu/hr of total input rating of all appliances in the space.
not less than 100 sq. in.
two openings required - one within 12 in. from ceiling, other within 12 in. from floor or bottom of the
enclosure.
minimum dimension of air openings shall be not less than 3 in.
b.
Combined spaces in different stories
Volume of spaces in different stories shall be considered as communicating spaces where spaces
connected by one or more openings in doors or floors having a total minimum free area of 2 in.
2
/1000
Btu/hr of total input rating of all appliances.
2.
Outdoor Air - Opening Sizes: When outdoor air is used to supply combustion air to the appliance space,
both openings must connect directly to the outdoors via ducts or connect to a crawl space or attic that
connects freely to the outdoors. Outdoor combustion air provided through opening(s) to the outdoors must be
made in accordance with the methods detailed below.
a.
Two Permanent Openings Method - Two permanent openings shall be provided, one commencing
within 12 in. of the top, and the other within 12 in. of the bottom of the enclosure. The openings shall
communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the
outdoors, as follows:
vertical ducts, minimum free area
=
1 in.
2
/4000 Btu/hr of total input rating of all appliances in the
space.
horizontal
ducts, minimum
free
area
=
1 in.
2
/2000 Btu/hr of total input rating of all appliances in the
space.
b.
One Permanent Opening Method - One permanent opening, commencing within 12 in. of the top of
the enclosure, shall be provided. The appliance shall have clearances of at least 1 in. from the sides and
back and 6 in. from the front of the appliance. The opening shall directly communicate with the outdoors
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 the following:
1 in.
2
/3000 Btu/hr of the total input rating of all appliances located in the enclosure.
Not less than the sum of the areas of all appliances’ vent connectors in the space.
3. Combination Indoor and Outdoor Air - Opening Sizes: The use of a combination of indoor and outdoor
combustion air shall be in accordance with the following:
a.
Indoor Air - Where used, openings connecting the interior spaces shall comply with opening sizes
calculated in accordance with “Indoor Air Opening Sizes” described previously.
b.
Outdoor Air - Outdoor opening(s) shall be located and sized in accordance with “Outdoor Air Opening
Sizes” described previously.
c.
Outdoor Opening(s) - The outdoor opening(s) size shall be calculated in accordance with the following:
The ratio of interior spaces shall be the available volume of all communicating spaces divided by the
required volume (i.e. 50 cubic ft per 1000 Btu/hr if 0.4 ACH or greater).
The outdoor size reduction factor shall be 1 minus the ratio of interior spaces.
The minimum size of outdoor opening(s) shall be the full size of outdoor opening(s) calculated in
accordance with “Outdoor Air Opening Sizes” described previously, multiplied by the reduction
factor. The minimum dimension of air openings shall not be less than 3 in.
