MFC Series Boiler Vent and Combustion Air Guide
TAG-0080_OG
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GF-148-V
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3/29/2023
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3.
Code Required Vent Terminations
The guidelines provided in this bulletin should be followed to comply with AERCO, UL, NFPA 54
(National Fuel Gas Code, ANSI Z223.1),
NFPA 31,
and in Canada: CSA B149.1-10
recommendations and regulations.
Vent terminations should be at least 4 feet below, 1 foot above or 4 feet removed horizontally
from any window, door or gravity air inlet of a building. Such terminations should extend beyond
the outside face of the wall by at least 6 inches.
Figure 1: Location and Piping of the Two Condensate Drain Ports
The bottom of the vent termination should be at least 12 inches above both finished grade and
any maximum snow accumulation level to avoid blocking the vent or air intake. The vent
termination should be least 3 feet above any forced-air building inlet within 10 feet. Design must
prevent flue gases from recirculating through the boiler air intake.
Vents should not terminate over public walkways or areas where condensate or vapor could
create a nuisance or be detrimental to the operation of regulators, meters or related equipment.
Discharges should not be located in high wind, wind-blocked areas or corners, or be located
directly behind vegetation. Discharges in these locations may cause the flue pressures to fluctuate
and result in flame instability. As a general rule, designs should minimize wind effects.
Wall and roof penetrations should follow all applicable codes and the vent manufacturer's
instructions. Vents should never be installed at less than required clearances to combustible
materials, as enumerated in UL, NFPA, CSA B149.1-10 or local codes "Double-
wall" or “Thimble”
assemblies are required when vents penetrate combustible walls or roofs.
Vertical discharges should extend at least 3 feet above the roof through properly flashed
penetrations, and at least 2 feet above any object within a 10-foot horizontal distance.
Vertical and horizontal discharges should be designed to prevent rain from entering the vent.
Large-mesh screens can be applied to protect against the entry of foreign objects but the 'free
area' should be at least equivalent to the flue cross-sectional area when unrestricted.
CONDENSATE TRAP
VENT OUTLET
CONNECTION
MFC BOILER
TO DRAIN
UNDER SIDE OF EXHAUST CHAMBER
SHOWING THE TWO CONDENSATE PORTS
CAUTION!
PORTS MUST BE PIPED
TOGETHER BEFORE THE TRAP.
DRAIN
PIPING
CONDENSATE
DRAIN PORTS
