Bard Bayrd Furnace 403293A - Manual (Page 59)

EXAMPLES USING COMMON
VENTING TABLES
Example 3: Common Venting Two Draft-Hood
Appliances
Example 4; Common Verting a Draft Hood Water
Heater with a Fan-Assisted Furnace
Suppose a 35,000 Btu/hr water heater is to be сотгтюп
vented with a 150,000 Btu/hr furnace using a common
vent with a total height of 30 feet. The connector rise is 2
feet for the water heater and 3 feet for the furnace.
Assume single-wall metal connectors will be used with
Type В vent. What size connectors and combined vent
should be used in this installation?
Solution - (Table 4 applies in this example)
Table 4 should be used to size single-wall metal vent
connectors attached to Type В vertical vert. In the vent
connector capacity Table 4, find the row associated with
a 30-Ft vent height. For a 2-Ft rise on the vent connector
for the water heater, read the shaded columns for draft-
hood-equipped appliances to find that a 3 inch diameter
vent connector has a capacity o1 37,000 Btu/hr.
Therefore, a 3 inch single-wall metal vent connector may
be used with the water heater. For a draft-hood-
equipped furnace with a 3-Ft rise, read across the
appropriate row to find that a 5 inch diameter vent
connector has a maximum capacity of 120.000 Btu/hr
(which is too small for the furnace) and a 6 inch diameter
vent connector has a maximum vert capacity of 172,000
Btu/hr. Therefore, a 6 inch diameter vent connector
should be used with the 150,000 Btu/hr furnace.
For the capacity of the combined vent, the lower portion
of Table 4 should be used. The combined vert capacity
required is 185,000 Btu/hr. Table 4 shows that the
combined vent capacity of a 6 inch diameter vent with a
30-Ft vent height is 257,000 Btu/hr. This is more than
adequate to handle the 35,000 Btu/hr input water heater
and the 150,000 Btu/hr input furnace.
In this case, a 35,000 Btu/hr input draft-hood-equipped
water heater with a 2 loot connector rise is to be common
vented with a 100,000 Btu/hr fan-assisted furnace with a
3-Ft connector rise. The common vent consists of a 30-
Ft rise of Type В vert. What are the recommended vent
diameters for each connector and the common vent?
Solution - (Table 4)
Water Heater vent Connector Diameter. Let us
assume the installer would like to use a single-wall metal
vent connector. Using Table 4, Vent Connector
Capacity, read down the Total Vert 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 that is
equal to or greater than the water heater Input rating.
The table shows that a 3 inch vent connector has a
maximum input rating of 37,000 Btu/hr. Since this is
greater than the water heater input rating, a 3 inch vent
connector is adequate. Furthermore, since the water
heater is equipped with a draft hood, there are no
minimum input rating restrictions.
Furnace Vent Connector Diameter. Again, let us
assume the installer would like to use a single-wall metal
vent connector. Using Table 4, 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 119,000 Btu/hr
and a minimum input rating of 85,000 Btu/hr. The
100,000 Btu/hr furnace in this example falls within this
range, so a 4 inch connector is adequate. If the furnace
would have had an input rating of 80,000 Btu/hr, than a