Bard Bayrd Furnace 403293A - Manual (Page 16)

C. Design considerations.
1. General considerations.
Avoid oversizing furnace for your application. Se­
lect a furnace model with a rated heating output
close to the calculated heating toad. This extends
the firing period, decreasing the potential for con­
densate formation in the vent.
a. Too small a vent cannot carry all combustion
products outdoors. Too large a vent will not vent
combustion products rapidly enough to avoid
potential for condensation. Refer to Venting Ad­
dendum for correct size vent.
b. Vent height must be a minimum of five feet.
Minimize vent connector horizontal runs to the
extent possible for best performance.
c. The designer must consider the building's ori­
entation, answering these questions. Will the
vent terminate outside the building where its op­
eration could be adversely affected by winds?
Could any adjacent buildings adversely affect
vent operation? Allowing for these factors can
reduce the possibility of downdraft conditions.
d. If your local experience indicates possible con­
densation problems, provide for draining and
disposal of venting system condensate.
2. Vent sizing.
a. Sometimes the horizontal distance from the fur­
nace to the vent or chimney is already given;
this is known as the horizontal vent connector
run. The vent or chimney height is also usually
given as is the Btuh input of the gas appliances
served by the vent.
Check these parameters to be sure the venting
system will work. Use approved engineering
practices, Venting Addendum, these instructions,
and Part 7 of current National Fuel Gas Code
ANSI Z223.1/NFPA 54. Use vent capacity tables
in Venting Addendum to check existing or new
vent sizes for CATEGORY 1 furnaces.
b. See Venting Addendum for single appliance
venting and multiple appliance (common) vent­
ing. For multi-story installations, refer to current
National Fuel Gas Code ANSI Z223.1/NFPA 54.
c. Minimum vent connector diameter from furnace
to vent or chimney is same as draft inducer col­
lar.
3. Vent connector.
a. Vent connectors must be made of noncombus­
tible, corrosion resistant material capable of
withstanding vent gas temperatures. They must
be thick enough to withstand physical damage
and be accessible for inspection, cleaning and
replacement.
14
b. Use Type B1 vent connectors in or through at­
tics, crawl spaces, or other cold areas. Install
thimbles that meet local codes when vent con­
nectors pass through walls or partitions of com­
bustible material.
c. Keep vent connectors as short as possible by
locating furnace as dose as practical to vent or
chimney. Avoid unnecessary turns or bends
which create resistance to
flow of vent gases.
Adding an elbow adds resistance. For example,
adding a 6" 90-degree elbow would be the
equivalent of adding 20 feet of horizontal 6" pipe.
45-degree elbows have lower resistance than 90-
degree elbows, and can work for most vent runs.
d. You may increase vent connector diameter to
overcome installation limitations and obtain con­
nector capacity equal to furnace input. Make this
increase as close as possible to draft inducer
collar, allowing for necessary adapters and fit­
tings.
e. If you join two or more vent connectors before
they enter the vertical vent or chimney, use cau­
tion. See Venting Addendum.
f. Do not connect this furnace to any portion of a
vent system which operates under positive pres­
sure. Positive pressure would result with CAT­
EGORY 3 and 4 appliances connected to the
vent.
g. Do not connect vent connector to a chimney flue
serving a fireplace unless you permanently seal
fireplace flue opening.
4. Vertical vent or chimney.
a. Vents and chimneys usually extend vertically with
offsets not exceeding 45-degrees. Consider vent
pipe runs more than 45'degrees as horizontal
runs. Include their length in the total horizontal
run.
b. Designer and installer must provide an appropri­
ately sized common vent for all appliances con­
nected to it. See Venting Addendum.
c. Connect this CATEGORY 1 furnace only to vent
systems with other CATEGORY 1 appliances.
WARNING: Do not connect this Category 1
furnace to a vent system used by Category 3
and 4 appliances. Do not connect It to vents
with mechanical draft systems operating at
positive pressure. Improper venting could al­
low combustion products to collect in struc­
ture during use, resulting In damage, Injury
or death.
5. Chimney.
Furnace is suitable for venting into a properly sized
and lined masonry chimney. Consult National Fuel
Gas Code ANSI Z223.1/NFPA 54 for construction
details. If chimney is oversized, liner is inadequate