8.2 Unvented Operation
Sufficient ventilation must be provided in the amount of 4 cfm per 1000 Btu/h firing rate (United States); 3 cfm per 1000 Btu/h firing rate (Canada).
Use of optional outside combustion air is not recommended with unvented heaters.
If exhaust fans are used to supply ventilation air, an interlock switch must be used to prevent the heater from coming on when the fans are off. This may be done using a pressure switch.
8.3 Horizontal Venting
In noncombustible walls only, vent terminal (P/N
For 4" (10 cm) vents in either combustible or noncombustible walls, use Tjernlund
For 6" (15 cm) common vents in either combustible or noncombustible walls, use Tjernlund
Follow the manufacturer's instructions for proper installation.
8.4 Vertical Venting
For 4'' (10 cm) common vent, an approved vent cap (P/N 90502300) must be used.
For 6'' (15 cm) common vent, an approved vent cap (P/N 90502302) must be used.
For common vertical venting of more than two heaters, See Page 38, Section 8.10.
A vent shall not extend less than 2' (0.6m) above the highest point where it passes through a flat roof of a building.
8.5 Unvented Operation Tube Termination
Turndown type vent terminal with a screen must be installed at the exhaust end of the tube. Vent terminal design shall not incorporate backdraft flap.
FIGURE 22: Tube Termination
8.6 Length Requirements
The maximum vent length allowed is 45' (13.7 m). The maximum outside air supply duct length allowed is 45' (13.7 m).
The total vent length, plus outside air duct length, plus any extensions to minimum heat exchanger lengths, cannot exceed 65' (19.8 m).
Vent length should be limited to less than 20' (6 m). If using vent lengths greater than 20' (6 m), condensation will form in the vent pipe. Insulation and additional sealing measures (high temperature silicone at all seams) are required. Optional heat exchanger beyond minimum lengths is considered as vent length for length determination.
Subtract 15' (4.6 m) of maximum allowed vent or duct length per vent elbow if more than two are used.
8.7 Horizontal Ventilation 4'' (10 cm) Pipe
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| SIDE VIEW |
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| Combustible or |
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Vent Adapter |
| Vent Adapter | |
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| 18" (46 cm) | |
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| Min. |
4" (10 cm) |
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Single Wall Pipe |
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| Vent Terminal |
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| 4" (10 cm) Single Wall Pipe | |
| Vent Terminal |
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Description | Part Number |
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Vent Terminal (Comb. Wall) | 90502100 |
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Vent Terminal |
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36 of 59 |
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