Hydronic Heating Boilers and Domestic Water Heaters Installation and Service Manual

1. Conventional Negative Draft
Venting
IMPORTANT: Before installing a venting system,
follow all venting clearances and requirements
found in the Venting, General Information
section, page 10.
Figure 14 - Conventional Negative Draft Vertical Venting
with Combustion Air Louvers
This option uses Type-B double-wall flue outlet piping. The
blower brings in combustion air. The buoyancy of the heated
flue products cause them to rise up through the flue pipe. The
flue outlet terminates at the rooftop.
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
With this venting option, you must use Type-B double-wall (or
equivalent) vent materials. Vent materials must be listed by a
nationally-recognized test agency for use as vent materials.
Make the connections from the unit vent to the outside stack as
direct as possible with no reduction in diameter. Use the
National Fuel Gas Code venting tables for double-wall vent to
properly size all vent connectors and stacks. Follow the vent
manufacturer's instructions when installing Type-B vents and
accessories, such as firestop spacers, vent connectors,
thimbles, caps, etc.
Provide adequate clearance to combustibles for the vent
connector and firestop.
When planning the venting system, avoid possible contact with
plumbing or electrical wiring inside walls, ceilings, and floors.
Locate the unit as close as possible to a chimney or gas vent.
Avoid long horizontal runs of the vent pipe, 90° elbows,
reductions and restrictions.
No additional draft diverter or barometric damper is required
on single unit installations with a dedicated stack and a
negative draft maintained between 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.
At the time of removal of an existing appliance, the following
steps shall be followed with each appliance remaining
connected to the common venting system placed in operation,
while other appliances remaining connected to the common
venting system are not in operation.
1. Seal any unused opening in the common venting system.
2. Visually inspect the venting system for proper size and
horizontal pitch. Make sure there is no blockage or
restriction, leakage, corrosion and other unsafe conditions.
3. If possible, close all building doors and windows. Close all
doors between the space in which the appliances remaining
connected to the common venting system are located and
other building spaces.
Installation and
Service Manual
13