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2
Venting
Barometric damper location
Any venting system option that requires a barometric
damper must adhere to the following directions for optimum
performance. The preferred location for the barometric damper
is in a tee or collar installed in the vertical pipe rising from the
unit's flue outlet. The barometric damper MUST NOT be
installed in a bull head tee installed on the unit's flue outlet.
The tee or collar containing the barometric damper should
be approximately three feet vertically above the connection to
the unit's flue outlet. This location ensures that any positive
velocity pressure from the unit's internal combustion fan is
dissipated and the flue products are rising due to buoyancy
generated from the temperature of the flue products. Adjust
the weights on the damper to ensure that draft is maintained
within the specified ranges.
1.
Conventional negative draft
venting
Before installing a venting system, follow
NOTICE
all venting clearances and requirements
found in the Venting, General Information
section, page 16.
Figure 2-6_Conventional negative draft vertical venting
with combustion air louvers
On a conventionally vented, negative draft appliance, the
connection from the vent to the chimney or vent termination
on the outside of the building MUST be made with listed Type
"B" double wall (or equivalent) vent connectors and must be
direct as possible with no reduction in diameter. To properly
size all double wall vent connectors and stacks, use the venting
tables in the latest edition of the National Fuel Gas Code, ANSI
Z223.1, in Canada, the latest edition of CGA Standard B149
Installation Code for Gas Burning Appliances and Equipment.
The Type "B" vent and accessories, such as firestop spacers,
thimbles, caps, etc., MUST be installed in accordance with the
manufacturer's listing. The vent connector and firestop must
provide correct spacing to combustible surfaces and seal to the
vent connector on the upper and lower sides of each floor or
ceiling through which the vent connector passes.
Any vent materials used must be listed by a nationally recognized
test agency for use as vent material.
18
Installation & Service Manual
Negative draft
The negative draft in a conventional vent installation must be
within the range of 0.02 to 0.08 inches w.c. to ensure proper
operation. Make all draft readings while the unit is in stable
operation (approximately 2 to 5 minutes).
Connect the flue vent directly to the flue outlet opening on
the top of the unit. No additional draft diverter or barometric
damper is needed on single unit installations with a dedicated
stack and a negative draft within the specified range of 0.02
to 0.08 inches w.c. If the draft in a dedicated stack for a single
unit installation exceeds the maximum specified draft, you
must install a barometric damper to control draft. Multiple unit
installations with combined venting or common venting with
other Category I negative draft appliances require each boiler
to have a barometric damper installed to regulate draft within
the proper range.
Do not connect vent connectors serving appliances vented by
natural draft (negative draft) to any portion of a mechanical
draft system operating under positive pressure. Connecting to a
positive pressure stack may cause flue products to be discharged
into the living space causing serious health injury.
Flue outlet piping
The negative draft in a conventional vent installation must be
within the range of 0.02 to 0.08 inches w.c. to ensure proper
operation. Make all draft readings while the unit is in stable
operation (approximately 2 to 5 minutes).
Connect the flue vent directly to the flue outlet opening on
the top of the unit. No additional draft diverter or barometric
damper is needed on single unit installations with a dedicated
stack and a negative draft within the specified range of 0.02 to
0.08 inches w.c.
Common venting systems
You can combine the flue with the vent from any other negative
draft, Category I appliance. Using common venting for multiple
negative draft appliances requires you to install a barometric
damper with each unit. This will regulate draft within the
proper range. You must size the common vent and connectors
from multiple units per the venting tables for Type-B double-
wall vents in the latest edition of the National Fuel Gas Code,
ANSI Z223.1 and/or CAN/CGA-B149 Installation Code.
Common venting systems may be too large when an existing
unit is removed.
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