Bard Bayrd Furnace 403293A - Manual (Page 60)

EXAMPLES USING COMMON
VENTING TABLES
Example 4; (cont'd)
Common Vent Diameter. The total input to the
common vent is 135,000 Btu/hr. Using Table 4,
Common Vent Capacity, read down the Total Vent
Height "H** column to 30 feet and across this row to find
the smallest vent diameter in the "FAN+NAT column
that has a Btu/hr rating equal to or greater thani 35,000
Btu/hr. The 4 inch common vent has a capacity of
132,000 Btu/hr and the 5 inch common vent has a
capacity of 202,000 Btu/hr. Therefore, the 5 inch
common vent should be used in this example.
Summary. In this example, the installer may use a 3
inch diameter, single-wall metal vent connector for the
water heater and a 4 inch diameter, single-wall metal vent
connector for the furnace. The common vent should be
a 5 inch diameter Type 8 vent.
Example 5: Single Draft Hood Equipped Furnace
Vented into A Masonry Chimney
A 135,000 Btu/hr draft hood equipped furnace is to be
vented into a 15' high tile lined masonry chimney. The
chimney is not exposed to the outside except above the
roof line. The furnace has a 6" diameter draft hood outlet
and requires a 10* lateral vent connector with 3 elbows.
The chimney is constructed using a 8" x 8*‘ liner. What
size single wall vent connector is required?
Solution:
Table 6 should be used. Refer to the figure for Example
5.
To determine the required vent connector diameter,
read down the height column in Table 6 until 15' is
found. Find the row for a 10' long lateral. The table shows
that a 6" diameter connector will allow a maximum
capacity of 151,000 Btu/hr for "Nat Max." (draft-hood
equipped) furnace. Because 3 elbows are required,
however, the maximum capacity must be reduced by
10% (See Note 3). Allowing for the additional elbow the
corrected maximum capacity is 135,900 Btu/hr. A 6"
diameter connector is large enough and should be
used. The internal area of the chimney is 8" x 8" = 64 sq.
in. and is within the acceptable range (38 sq. in to 198
sq. in.) for a 6" vent connector as shown in Table 6.
Example 6: Common venting into a Masonry Chimney
In this case, a 35,000 Btu/hr input 4 inch diameter outlet
draft hood-equipped water heater with 2 feet of
connector rise and 4 feet of horizontal length is to be
common vented with a 100,000 Btu/hr fan-assisted
furnace with a 4 inch diameter flue collar, 3 feet of
connector rise and 6 feet of horizontal length. The
common vent is an 8 x 12 tile lined chimeny that is 30
feet tall. What are the recommended vent diameters for
each connector? Is this an acceptable installation?
Solution
Table 8 is used to size common venting installations
involving single wall connectors into masonry chimneys.
Water Heater Vent Connector Diameter. Using
Table 8, Vent Connector Capacity, read down the Total
Vent Height "H" column to 30 feet and read across the 2
ft Connector Rise "R" row to the first Btu/hr rating in the
"NAT MAX" column tehat is equal to or greater than the
water heater input rating. The Table shows that a 3 inch
vent connector has a maximum input of only 31,000
Btu/hr while a 4 inch vent connector has a maximum
input of 57,000 Btu/hr. A 4 inch vent connector must
therefore be used.
Furnace Vent Connector Diameter. Using Table 8
Vent Connector Capacity, read down the Total Vent
Height "H" column to 30 feet and across the 3 ft
Connector Rise "R" row. Since the furnace has a fan-
assisted combustion system, find the first "FAN MAX"
column with a Btu/hr rating greater than the furnace input
rating. The 4 inch vent connector has a maximum input
rating of 127,000 Btu/hr and a minimum input rating of
95,000 Btu/hr. The 100,000 Btu/hr furnace in this
example falls within this range, so a 4 inch connector is
adequate.
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