VS80-130
Natural Draft - Installation & Operation Instructions
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Triton
11
Combustion Air
Natural Draft appliances require an adequate amount of combustion air to sustain proper combustion and prevent
flue gas leakage. The appliance’s air-inlet draws combustion air from Indoors or Outdoors depending on whether
there is a sufficient natural infiltration (air changes) occurring to sustain combustion. If the building is newer and
relatively air tight, outdoor air should be considered. For recommended practice, refer to NFPA 31 (USA) or
CSA B139 (Canada).
Air Circulation
- The boiler shall be located so as not to interfere with proper circulation
of combustion, ventilation, and dilution air.
Make-up Air
- The operation of exhaust fans, kitchen ventilation systems, clothes dryers,
and fireplaces must be considered in determining the adequacy of a space to provide
combustion air requirements. Failure to ensure adequate make-up air to all appliances
may result in flue gas leakage, personal injury or death.
Permanent Openings for Combustion Air
The appliance space or boiler area requires a permanent opening(s) capable of providing adequate combustion air
to the boiler. If using two permanent openings, one opening must be within 12 inches of the ceiling, the other
within 12 inches of the floor. The minimum dimension of air openings to the appliance space shall not be less
than 3 inches in any one direction, including rectangular ducts. Round ducts are connected to the permanent air
openings; duct sizes must have a minimum cross-sectional area of 3 inches. See
“Sizing Combustion Air
Openings”
for more details.
The minimum size of permanent openings and how combustion air is supplied to them depends on three factors:
1.
What is the input capacity of the boiler in Btu/hr?
2.
How is the Combustion Air being supplied?
3.
Is make-up air required for other appliance in the room competing for the same air?
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.
