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LDAP-IOM (01-22) 207733-A
Combustion Air Requirements
⚠ WARNING ⚠
• Do not install a unit in a confined space without providing wall openings leading to and from
the space.
• A model LDAP power-vented heater is designed to take combustion air from the space in which
the heater is installed and is not designed for connection to outside combustion air intake ducts.
Connecting outside air ducts voids the warranty and could cause hazardous operation.
•
This heater must be supplied with the air that enters into the combustion process and is then vented to the outdoors .
Sufficient air must enter the equipment location to replace that exhausted through the heater vent system . In the
past, the infiltration of outside air assumed in heat loss calculations (one air change per hour) was assumed to be
sufficient . However, current construction methods using more insulation, vapor barriers, tighter fitting and gasketed
doors and windows, weather-stripping, and/or mechanical exhaust fans may now require the introduction of outside
air through wall openings or ducts .
•
Under all conditions, enough air must be provided to ensure there will not be a negative pressure condition within
the equipment room or space .
•
Requirements for combustion air and ventilation air depend upon whether the unit is located in a confined or
unconfined space . A
confined
space is defined as a space whose volume is <50 cubic feet per 1,000 BTUh of
the installed appliance input rating . An
unconfined
space is defined as a space whose volume is
≥
50 cubic feet
per 1,000 BTUh of the installed appliance input rating .
•
Provide openings (depending on the combustion air source) near the floor and ceiling for ventilation and air for
NOTE: For further details on supplying combustion air to a confined space, refer to the National
Fuel Gas Code ANSI Z223.1a (latest edition).
Figure 6. Confined Space Combustion Air Openings (Refer to
)
CONFINED
SPACE
A
A
B
B
C
C
Table 5. Determining Confined Space Combustion Air Requirements
Letter
*
Air Source
Required Opening Size
Calculate Combustion Air
Requirements
A
Air inside building
1 square inch free area per 1000 BTUh
Add total BTUh of all appliances in
confined space and divide by figures
at left for square inch free area size of
each (top and bottom) opening
Never <100 square inches free area for each opening
B
Outside air through duct
1 square inch free area per 2000 BTUh
C
Direct outside air
1 square inch free area per 4000 BTUh
*
