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MFC Series Boiler Vent and Combustion Air Guide
Figure 10 illustrates the preferable "transition vent section" when making the 45° connection into
a main. The main can also remain at one diameter, as long as it is sized for the total number of
units vented and the 45° branch connection is retained. Use of the recommended "transition"
assembly will reduce the overall system pressure drop.
Figure 10: Required Transition Vent Sections
The vent system should always be pitched up ¼-inch per foot of run towards the vent termination
(see Figure 11). This will enable condensate to drain back to the unit for disposal. Low spots in
the vent must be avoided. Inspect periodically to ensure correct drainage.
As shown in Figure 11, the unit at the end of the vent main must be connected via an elbow. An
end cap must not be used as it may cause vibration and flue pressure fluctuations.
As discussed previously, the static regain method should not be used for common ductwork, but
rather, the one duct size should be used for the common run.
MFC vents should never be interconnected to those connected to other manufacturers'
equipment.
Figure 11: Connection of Unit at End of Vent Main
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3/29/2023
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