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B. Removing an Existing Boiler From a Common Chimney
Read this only if the FCM boiler is replacing an existing boiler that is being removed from a common chimney.
This section does not apply to the installation of a FCM boiler.
In some cases, when an existing boiler is removed from a common chimney, the common venting system may be
too large for the remaining appliances. At the time of removal of an existing boiler, the following steps shall be followed
with each appliance remaining connected to the common venting system placed in operation, while the other appliances
remaining connected to the common venting system are not in operation.
(a) Seal any unused openings in the common venting system.
(b) Visually inspect the venting system for proper size and horizontal pitch and determine there is no blockage
or restriction, leakage, corrosion and other defi ciencies which could cause an unsafe condition.
(c) Insofar as practical, close all building doors and windows and all doors between the space in which all the
appliances remaining connected to the common venting system are located and other spaces of the building.
Turn on clothes dryers and any appliance not connected to the common venting system. Turn on any exhaust
fans, such as range hoods and bathroom exhausts, so they will operate at maximum speed. Do not operate a
summer exhaust fan. Close fi replace dampers.
(d) Place in operation the appliance being inspected. Follow the lighting instructions. Adjust thermostat so the
appliance will operate continuously.
(e) Test for spillage at the draft hood relief opening after 5 minutes of main burner operation. Use the fl ame of a
match or candle, or smoke from a cigarette, cigar, or pipe.
(f) After it has been determined that each appliance remaining connected to the common venting system
properly vents when tested as outlined above, return doors, windows, exhaust fans, fi replace dampers and any
other gas-burning appliances to their previous condition of use.
(g) Any improper operation of the common venting system should be corrected so the installation conforms
with the National Fuel Gas Code, ANSI Z223.1. When re-sizing any portion of the common venting system,
the common venting system should be re sized to approach the minimum size as determined using the
appropriate tables in Part 11 of the National Fuel Gas Code, ANSI Z223.1.
WARNING
NEVER COMMON VENT A FCM BOILER WITH OTHER APPLIANCES
Figure 7.9: Vertical Twin Pipe Vent System (Vent Option 5)