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VZ-VZH-VZT-IOM (08-24) 1047121-A
Figure 24. Category III Common Horizontal Venting
Combustion Air Connections
⚠ CAUTION ⚠
• IMPORTANT: If the building has a slight negative pressure or if corrosive contaminants such
as halogenated hydrocarbons are present in the air, an outside supply of combustion air to the
heater is required.
• Seal all combustion air pipe joints.
• The use of optional outside combustion air is not recommended with unvented heaters.
• The air supply duct may have to be insulated to prevent condensation on the outer surface.
• The combustion air terminal must maintain a minimum distance of 3 feet (93 cm) from the vent
termination for both vertical and horizontal venting. A vertical combustion air terminal must not
extend >1-foot higher above the roof than a vertical vent terminal.
• Heaters with a common combustion air pipe must be controlled by a common thermostat.
Installations That Require Outside Combustion Air
For installations that require outside combustion air, make connections in accordance with Figure 25 or Figure 26
using field-supplied piping and either an optional or field-supplied vent cap. Connect to the flange on the blower for
models VZ and VZT or to the combustion air inlet collar on model VZH.
NOTE: Flex hose is recommended for connecting to the unit, but solid pipe is acceptable.
OUTSIDE WALL
OUTSIDE WALL
6-INCH VENT TERMINAL
FIELD-SUPPLIED
SWEEPING TEE
FIELD-SUPPLIED
SWEEPING Y
VENT ADAPTER
VENT ADAPTER
VENT ADAPTER
VENT ADAPTER
6-INCH SINGLE-WALL
6-INCH SINGLE-WALL
4-INCH SINGLE-WALL
4-INCH SINGLE-WALL
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