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MFC Series Boiler Vent and Combustion Air Guide
10. Corrections for Altitude
Table 7 in Section 19 lists correction factors for installation altitudes above sea level. These
factors must be applied to both the natural draft and pressure drops of vent and air ducts. The
pressure drop through vents and combustion air ducts will increase at higher elevations, while the
natural draft will decrease.
11. Manifolded Systems
In many instances it may be practical to connect multiple units using a manifolded vent or exhaust
configuration. However, when multiple units are connected by a manifolded air intake or exhaust
vent, the operation of a given unit can be affected by the others, if the venting or combustion air
system is not designed properly. Properly designed common vent and air supply systems can be
installed that will prevent "operational interaction" between units.
Do not use static regain method on common ductwork, but rather, use one duct size for
the common run (See Figure 11 in Section 18).
Contact your AERCO sales representative or AERCO International for design assistance
and review when designing manifolded exhaust and manifolded combustion air systems.
12. Elbow Quantity and Separation
The quantity and angle of elbows and the distances between them can influence the system's
exhaust and combustion air pressures, as well as its acoustical behavior. Designers should
consider minimizing the quantity of elbows in the design and the use of angles less than 90°,
whenever possible. Five or fewer elbows are recommended for individual venting/connections;
five or fewer are recommended for common sections. The minimum distance required between
two elbows is five feet.
13. Exhaust Muffler And Air Inlet Attenuator Guidelines
MFC Series boilers require an exhaust muffler when installed in a noise-sensitive application and
when the exhaust vent ducting is relatively short in length. The following criteria should be used
to determine when to include a field-installed muffler in a MFC series installation:
•
The exhaust is sidewall vented and the vent is terminated in close proximity to
residences, offices, hotel/hospital rooms, classrooms etc.
OR
•
The total vertical and horizontal section of exhaust vent is less than 25 linear feet in
length from the last unit, and the vent terminates in close proximity to residences, offices,
hotel/hospital rooms, classrooms etc.
For manifolded exhaust systems, the total vertical section length includes both horizontal and
common vertical; individual boiler vertical connectors are included in the determination as well.
EXAMPLE: For an installation that has a 20-foot common vertical, 5-foot common horizontal
after the last boiler, and each boiler has a 10-foot vertical connector, the total section linear
length considered is 35 feet. Because this length is greater than 25 linear feet, a muffler is not
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