Buderus GB125BE-22 Guide

For Buderus models:
- GB125BE-22/30/35
Design Manual
GB125 Concentric Vent

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice

Applications manual
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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
Table of Contents
1 General information 5
1.1 This manual 5
1.2 Standards, regulations and directives 5
1.3 System certication 5
2 Safety 6
2.1 Intended use 6
2.2 Layout of the instructions 6
2.3 Please follow these instructions 6
2.4 Tools, materials and accessories 6
2.5 Disposal 6
3 Description of systems 7
3.1 Scope 7
3.2 Available systems 7
4 General requirements 8
4.1 Installation requirments for the boiler room 8
4.2 Condensate drain 8
4.3 Annual inspection 8
4.4 Safety distances to combustible material 8
4.5 Terminations 8
4.6 Instructions for inspection and clean-out
sections 8
5 Installing the ue gas system 9
5.1 General installation notes 9
5.2 Trimming pipes 9
5.3 Installing the pipes 9
5.4 Pipe disassembly 10
5.5 Appliance connection 10
5.6 Installation and nal assembly 10
6 Inspecting the ue gas system 11
7 Direct Vent - HTK Venting System kit 12
8 Vertical Vent - DO Venting System kit 13
9 Chimney Liner - GAK Venting System kit 15
9.1 Installation in an existing chimney shaft 17
9.2 Installation of rigid chimney pipe 18
9.3 Flexible chimney liner - GAK system with
UB ex 21
9.4 Accessories for GAK systems 24

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice

Applications manual
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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
1. General information
1.1. This manual
These instructions contain important information for the
safe and appropriate installation of the ue gas systems
and system startup.
It is a design guide for the venting system of the Buderus
GB125 boiler, and it describes the prepackaged kits and
their accessories, as well as important design
considerations. It is intended for the installer during the
planning phase and the actual installation.
These instructions are designed for specialists, who -
through their training and experience - are knowledgeable
in the installation and servicing of heating systems and oil
installations.
This document is a supplement to the boiler manuals and
the instructions included with the venting system.
1.2. Standards, regulations and directives
It is the responsibility of the installer to ensure that the
system corresponds to all current building codes and
regulations.
1.3. System certication
For Buderus GB125 oil condensing boilers:
The GB125 is system-certied with this ue gas system for
the USA and Canada by CSA International.
An individual approval of the ue gas system is not
required.
The ue gas system must be installed in accordance with
the installation instructions. The maximum permissible
overall length and the number of changes of direction are
specied on page 7.

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
2. Safety
2.1. Intended use
This concentric venting system may be used as ue gas
system for Buderus oil condensing boilers with maximum
ue gas temperatures of 248 °F (120 °C). Suitable are
boilers of the types:
– Logano plus GB125BE-22/30/35
2.2. Layout of the instructions
Two levels of danger are identied and signied by the
following terms:
WARNING! RISK OF FATAL INJURY
Identies possible dangers emanating from a
product, which might cause serious injury or
death if appropriate care is not taken.
CAUTION! RISK OF INJURY/SYSTEM
DAMAGE
Indicates a potentially dangerous situation that
could cause minor or moderately serious
injuries and damage to property.
Additional symbols for identication of dangers and user
instructions:
USER NOTE
User tips for optimal use of equipment and
adjustment as well as other useful information.
2.3. Please follow these instructions
WARNING! RISK OF FATAL INJURY FROM
FLUE GAS AND CARBON MONOXIDE
POISONING.
Insufcient ventilation or leaky ue gas pipes may
cause dangerous ue gas leaks.
– Ensure that air intake or exhaust air vents are
not closed off or their size reduced.
– The boiler must not be operated until the
obstruction has been removed.
– Inform the system user in writing of the fault
and its associated dangers.
WARNING! RISK OF DEATH FROM FALLING.
Take sufcient measures to prevent accidents on
the roof.
Use state of the art safety equipment and take
common sense safety measures.
WARNING! RISK OF INJURY OR DEATH FROM
TOOLS AND EQUIPMENT FALLING FROM THE
ROOF.
Secure tools and equipment against falling from
the roof.
Only use original Buderus spare parts.
Damage caused by the use of parts not supplied
by Buderus is excluded from the Buderus
warranty.
2.4. Tools, materials and accessories
For the installation of the boiler, you will need standard
tools used for central heating, oil boiler and DHW water
systems.
Additional tools needed are described in the appropriate
section of these instructions.
2.5. Disposal
– Dispose of the packaging of the ue gas system in an
environmentally responsible manner.
– Dispose of defunct components of the ue gas system
through an authorized agent in an environmentally
responsible manner.

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
3. Description of the systems
3.1. Scope
The concentric venting system described in this manual
is used exclusively for the Buderus GB125 boiler. No
other venting system can be used with this boiler, and the
venting system can not be used in conjunction with any
other boiler.
Do not replace or substitute any vent or combustion air
pipe with another brand, make, model, or material.
The Buderus GB125 is designed for balanced ue
operation only. All combustion air is drawn from the
outdoors. Use of balancers or barometric dampers dees
the system principle and is not permitted.
Installation and service of Buderus concentric venting
systems must be performed by a trained installer.
CAUTION! Never connect this concentric vent to
a common venting system
3.2. Available systems
The three types of systems that are available are shown
in Fig. 1:
Observe the maximum vent lengths for each boiler size
as shown in Table 1.
Systems are available as prepackaged kits that include
the essential components needed in every installation.
Refer to the descriptions of the individual system for
included items. For most systems extra straight pipe and
additional elbows must be purchased as needed. See list
of accessories for every system.
The GAK system draws combustion air from the
roof and may not be suitable for installation in
multi-ue chimneys, where a second ue vents a
combustion appliance that is used on a regular
basis. Flue gases could be drawn in with GB125
combustion air and cause system interruption.
HTK - Direct vent through
side wall
(See page 12)
Part Number: 7747310386
DO - Vertical vent through
conditioned and uncondi-
tioned space (NOT -suitable
for installation outdoors)
(See page 13)
Part Number: 7747200752
GAK - Liner inside an existing
chimney;
Option 1: rigid pipe for a
straight chimney;
Option 2: flexible liner for
chimneys with an offset or
bend;
(See page 15)
Part Number: 7747200755
Fig.1 Available systems
Max. length of ue pipe, feet (m)
Buderus ue pipe systems DN 80/125 Table 1
Boiler Size HT-K direct
vent
DO
vertical vent
GAK
chimney
liner
GB125 - 22 17' (5.2 m) 51' (17 m) 51' (17 m)
GB125 - 30 17' (5.2 m) 64' (21 m) 64' (21 m)
GB125 - 35 17' (5.2 m) 71' (23 m) 71' (23 m)
The overall lengths include two elbows for the HT-K, and
one elbow for the DO and GAK kits. Every additional
elbow (accessory) reduces the maximum vent length by 3
ft (1 m).

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
4. General requirements
4.1. Installation requirements for the boiler
room
The GB125 is designed for balanced ue operation only.
All combustion air is drawn from outdoors.
Allow ample room at the back of the boiler for servicing of
the secondary heat exchanger.
4.2. Condensate drain
The boiler has an integrated condensate drain in the
secondary heat exchanger. The condensate from the vent
pipe ows directly into the boiler’s trap (siphon). This
requires that all horizontal vent pipes are pitched at ⅝
inch per foot (55 mm per meter) toward the appliance,
including the horizontal termination (HTK-kit only). No
second condensate drain is needed.
Note that the siphon oat must be cleaned at
least once a year to ensure safe and proper
operation.
The Buderus GB125BE boiler comes with a condensate
neutralizer that must be properly maintained. Follow local
rules when draining condensate into municipal sewage
systems. It is not recommended to drain untreated
condensate into septic systems. In any case follow local
codes and regulations.
4.3. Annual inspection
The venting system must be inspected annually for signs
of damage or condensate leaks. If the venting system
appears damaged, the appliance must be turned off and
the venting system repaired.
4.4. Safety distances to combustible material
The design of the concentric venting system allows
installation with zero (0” (0 mm)) clearance to
combustibles. Therefore, no particular protective
measures or safety distances are required to combustible
material or furniture.
4.5. Terminations
Terminations must be so positioned as to avoid products
of combustion entering openings into buildings or other
ues or vents.
The Buderus concentric vent is designed for indoor
installation in conditioned and unconditioned spaces only.
Only the end of the termination is protected from UV-
radiation (direct sunlight) and the weather. None of the
other pipes or elbows may be installed outdoors.
4.6. Instructions for inspection and clean-out
sections
Local codes and regulations may require access to the
vent pipe for inspection and clean-out. Buderus offers an
inspection and clean-out section that allows inspecting
and cleaning the venting system without dismantling.
Table 2
Part number Description
87094587 clean out straight pipe
Note that the GAK chimney liner basic kit
includes the above clean out section.
The inspection and clean-out section (Fig. 9, page 15)
must be installed sideways in the horizontal section of the
ue gas pipe as the rst section after the boiler adapter.
Keep an area of at least 3 ft. x 3 ft. (1 m x 1 m) clearance
in front of the inspection section for access.
An upper inspection section may be needed if there are
any changes in direction, e.g. when elbows are used to
create an offset. Install the inspection and clean-out
section in the horizontal run above the change in
direction.
Keep an area of at least 1-1/2 ft. x 1-1/2 ft. (0.5 m x 0.5
m) clearance in front of the upper inspection section for
easy access.

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
5. Installing the ue gas system
5.1. General installation notes
WARNING! RISK OF DEATH FROM LEAKING
FLUE GASES.
Improper installation of venting system and
components or failure to follow all installation
instructions can result in property damage or
serious injury.
5.2. Trimming pipes
CAUTION! RISK OF INJURY FROM SHARP
EDGES.
Wear work gloves.
– With concentric pipes, pull the inner pipe out of the
outer pipe in the direction of the gasket.
– Trim pipes at a right angle to the required length x
(Fig. 2).
– Trim the same length off the ue gas and air intake
pipes.
– Carefully remove burrs from cut edges; otherwise
gaskets will get damaged, which can result in the
system no longer being air tight and condensate to
leak.
– Reinstall the ue gas and air intake pipes.
5.3. Installing the pipes
Pipes are assembled so that the sleeve points in the
direction of the ue gas stream, with the gasket on the far
side of the pipe when viewed from the boiler. Only use
original Buderus ue gas pipe gaskets!
– Coat the gaskets (Fig. 3 Item 1) and pipe ends with
CENTROCERIN®
gasket lubricant (supplied with the basic kit).
– Push the ue gas pipes (Fig. 3 Item 2) into one another
with a slight turning motion until the stop.
– With concentric pipes, push the combustion air pipe
(Fig. 3 Item 2) together to ensure a tight t.
– Verify that the gaskets did not shift.
– Never use screws to hold pipe together.
– If needed suspend pipe from the ceiling or the oor.
Fig. 2 Cuttting pipes
X: Desired length
Fig. 3 Pipe assembly
1: Location of the gaskets
2: Flue pipe
3: Combustion air pipe

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GB125 Concentric Vent
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GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
5.4. Pipe disassembly
Pull the pipes apart while turning slightly.
5.5. Appliance connection
To install the appliance connector on the boiler, identify
the gasketed connection in the bottom right corner at the
back of the boiler.
Apply CENTROCERIN® gasket lubricant on the gasket of
the secondary heat exchanger and on the mating adapter
pipe, and assemble with a slight turning motion. The
combustion air pipe should be oriented in a 10-o’clock
position with all 3 predrilled screw holes visible. (Fig. 4).
Use the supplied brackets and self tapping screws to
attach the adapter to the rear boiler panel.
Connect the combustion air hose to the adapter and
secure with the provided hose clamp.
5.6. Installation and nal assembly
(1) Install the termination.
(2) Follow the installation instructions to waterproof
the penetration. Follow standard industry practice
and consult a specialist if needed.
(3) On the boiler install a clean out section immediately
after the boiler adapter (if applicable).
(4) Connect the termination with the boiler using straight
concentric pieces and concentric elbows as required
by the installation site. Sections can be cut to length
per the procedure shown on page 9.
(5) After cutting to the appropriate length, coat gaskets
and mating pipes with CENTROCERIN® gasket
lubricant and slide the pieces together with a slight
turning motion.
(6) Sections longer than 6 ft. (2 m) must be supported
with bracing or clamps. Do not use the termination or
the boiler adapter to support the venting system.
It is the installer’s responsibility to ensure that the
vent pipe is securely attached and supported as
required by the site, and cannot accidentally
disintegrate.
Fig. 4 Appliance connection

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
6. Inspecting the ue gas system
To ensure that no leaks occur during operation, the venting
system must be checked for leaks before startup.
The ue gas line is sufciently tight if the combustion air
intake at the boiler adapter measures no higher than 0.2%
CO², or a minimum of 20.6% O² (ring gap test).
WARNING! RISK OF FLUE GAS POISONING.
Leaky ue gas lines may cause dangerous ue gas
leaks.
Take the boiler out of operation until the leak in the
ue gas line has been eliminated.

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
7. Direct Vent – HTK Venting System kit
The HTK kit contains essential pieces for a concentric
pipe-in-pipe direct vent application with sealed
combustion from boiler to termination (Fig. 5).
The kit (Fig. 5, Table 3) comes complete with a direct vent
termination, 2 elbows, the boiler adapter, and some
straight pipe. If needed, additional straight pipe sections,
an inspection and clean out piece, as well as additional
elbows must be purchased separately. See table 4 for a
complete list of accessories.
Choosing the right location for the terminal is critical to
proper and safe operation of the appliance. Consult the
HTK Installation Manual for details and limitations of the
direct venting system.
A ⅝ inch per foot (55 mm per meter) pitch to the
appliance is needed for all horizontal pipe runs including
the termination.
Inform the homeowner or system operator of the potential
appearance of a steam plume in cold climates.
Ice can develop on the termination in cold climates.
Ensure that ice formation does not pose a hazard on
public walkways.
Each boiler must be vented with a separate system.
In the Commonwealth of Massachusetts a direct
vent boiler is required to be accompanied by CO
detectors per 527 CMR 31.00.
Included items in basic kit
Before starting any installation work, ensure that all
included items are present (Table 3), plus any additional
pieces (Table 4) needed to complete the job.
Table 3
Part Number Description Qty
1 7747016312 Concentric boiler connector
DN80/125 for GB125
1
2 87094574 Concentric Elbow DN80/125x87
- 90 degrees
2
3 87094560 Concentric Pipe DN80/125x1000
– 39“ (1000mm)
1
4 7747213564 Concentric Wall Termination
DN80/125 with inside and outside
ashings
1
Fig. 5 HTK-kit
Table 4
Part Number Description
87094587 Concentric inspection pipe
87094556 Concentric Pipe DN80/125x500 19“ (500 mm)
87094560 Concentric Pipe DN80/125x1000 39“ (1000 mm)
87094600 Concentric Pipe DN80/125x2000 78“ (2000 mm)
87094580 Concentric Elbow DN80/125x15 15 degrees
87094576 Concentric Elbow DN80/125x30 30 degrees
87094570 Concentric Elbow DN80/125x45 45 degrees
87094574 Concentric Elbow DN80/125x87 90 degrees

Applications manual
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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
8. Vertical Vent – DO Venting System kit
The DO kit (Fig. 6) is suitable for new construction and
retrots, and allows a quick and simple chimney
installation through the roof.
The DO-kit contains essential pieces for a concentric
pipe-in-pipe vertical vent application with sealed
combustion from boiler to termination.
Each boiler must be vented with a separate system.
The kit (Fig. 6) comes complete with a vertical
termination, the boiler adapter, and some straight pipe.
Additional straight pipe sections, an inspection and clean
out piece, a suitable roof jack or collar (Fig. 7 & 8), as
well as at least one elbow must be purchased separately.
Included items in basic kit
Before starting any installation work, ensure that all
included items (Table 5) are present, plus any additional
pieces (Table 6) needed to complete the job.
Table 5
Part Description Qty
1 7747016312 Concentric boiler connector
DN80/125 for GB125
1
2 87092168 Adjustable face plate 1
3 87092172 Rafter support clamp 1
4 87090520 Adapter pipe 1
5 87090520 Concentric extension pipe 1
6 87090528 Concentric vertical roof termination
black
1
Install all horizontal runs with a 5/8 inch per foot (55 mm
per meter) pitch to the appliance to allow condensate to
drain properly.
Fig. 6 DO-kit
Fig. 7 Flat roof collars
Fig. 8 2-piece roof jack for sloped roofs

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
Accessories for DO System
Select the appropriate roof jack or collar for the
application based on roof pitch and roof type. It is
recommended to consult a professional roong contractor
to ensure structural damage to the building from leaks is
avoided.
Table 6
Part Number Description
87094912 Roof collar at roof H x DIA 3-1/2”x19-
1/2”(90x500mm) for DO-system
87094904 Roof collar at roof H x DIA 9-1/2”x19-
1/2”(240x500mm) for DO-system
87094812 Roof jack 5-25° (12/1 to 12/6 pitch) for DO-
system
87094814 Roof jack 35-55° (12/8 to 12/18 pitch) for DO-
system
87094587 Concentric inspection Tee
87094556 Concentric Pipe DN80/125x500 19“ (500mm)
87094560 Concentric Pipe DN80/125x1000 39“ (1000mm)
87094600 Concentric Pipe DN80/125x2000 78“ (2000mm)
87094580 Concentric Elbow DN80/125x15 15 degrees
87094576 Concentric Elbow DN80/125x30 30 degrees
87094570 Concentric Elbow DN80/125x45 45 degrees
87094574 Concentric Elbow DN80/125x87 90 degrees
For more details consult the DO installation manual.

Applications manual
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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
9. Chimney Liner – GAK Venting System
kit
Use the GAK kit for installations with an existing masonry
chimney in good condition. It consists of concentric
DN80/125 pipe-in-pipe from the boiler to the chimney, and
inside the chimney chase a sealed DN80 plastic ue gas
pipe runs up to the termination at the top. The space
surrounding the ue gas pipe is used to draw combustion
air from the roof to the boiler.
The GAK System ensures a sealed combustion system
from the boiler to the termination.
The GAK system draws combustion air from the
roof and may not be suitable for installations with
multi-ue chimneys, where a second ue vents a
combustion appliance that is used on a regular
basis. Flue gases could be drawn in with GB125
combustion air and cause service calls.
For installations in multi-ue chimneys with a risk of
ambers from wood stoves or similar appliances
reaching the top of the chimney, optional stainless
steel terminations are available. See list of
accessories (Tables 8-10).
Minimum chimney chase dimensions to ensure sufcient
supply of combustion air:
Rectangular: 5” x 5” (120 mm × 120 mm)
Round: DIA 5-1/2” (Ø 130 mm);
If the chimney is not a straight run but has an offset or
bend, you can still use the rigid pipe as long as the
bottleneck is accessible for the installation of elbows. If
inaccessible, use the GAK system with the UB Flex pipe
(Page 21) instead.
CAUTION! Never connect this concentric vent to a
common venting system
The chimney ue must not be used with any other
appliance or for any other purpose, must be in good
condition, and must be thoroughly cleaned before
conversion to GAK.
You will need to purchase the basic kit GAK (DN125/80) in
any case. For the content see Table 7 and Fig. 9. Select
additional items and accessories from Tables 8-10 as
needed.
Fig. 9 GAK basic kit

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GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
Included items in the GAK basic kit:
Table 7
Description Qty
1Concentric boiler adapter 1
2Concentric inspection Tee-joint 1
3Concentric pipe, DN125/80 39” (1000 mm) 1
4 Concentric chimney penetration DN125/80 and
chimney face plate, DN125
1
5Load bearing elbow, DN 80, with bracing and
support rail
1
62-Piece chimney spacer (set of 6) 1
7Termination, black , DN80, L = 20” (500 mm) and
ue gas end pipe, black
1
8CENTROCERIN® gasket lubricant (not shown) 1
Accessories for GAK System:
Table 8
Part Number Description
87094556 Concentric Pipe DN80/125x500 19“ (050mm)
87094560 Concentric Pipe DN80/125x1000 39“ (1000 mm)
87094600 Concentric Pipe DN80/125x2000 78“ (2000 mm)
87094580 Concentric Elbow DN80/125x15 15 degrees
87094576 Concentric Elbow DN80/125x30 30 degrees
87094570 Concentric Elbow DN80/125x45 45 degrees
87094574 Concentric Elbow DN80/125x87 90 degrees
Rigid Pipe for inside the chimney:
Table 9
Part Number Description
87092078 Single Pipe DN80x250 9.5“ (250mm)
87094588 Single Pipe DN80x500 19” (500mm)
87094592 Single Pipe DN80x1000 39“ (1000mm)
87094596 Single Pipe DN80x2000 78“ (2000mm)
87094652 Single Pipe Elbow DN80x15 15 degrees
87094648 Single Pipe Elbow DN80x30 30 degrees
87094644 Single Pipe Elbow DN80x45 45 degrees
87094614 2-Piece chimney spacer
87094920 Stainless Steel Chimney Cover (for rigid pipe only)
Inside a chimney with inaccessible offset:
Table 10
Part Number Description
87094036 UB-Flex kit DN83x12500 Flexible ue gas pipe
40ft. (12.5m) Spacers (8)
87092180 Chimney Top End Pipe (not needed with stainless
steel chimney cover)
87094668 Union for two UB Flex pipes (for tall chimneys
>40ft. or repairs)
87094672 Union from GAK rigid vent pipe to UB Flex pipe
87094614 2-Piece chimney spacer
87094676 Inspection and cleanout Tee for UB Flex
(for installation inside the chimney)
7747208685 Stainless Steel Chimney Cover (for UB Flex only)

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GB125 Concentric Vent
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GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
9.1. Installation in an existing chimney shaft
Before starting any installation work, ensure that all
included items are present, plus any additional pieces
needed to complete the job.
The chimney must be thoroughly cleaned before
installing the ue gas system. It is recommended
to use a professional chimney sweep.
If the chimney cannot be sufciently cleaned, and
dust generation is anticipated or residue of oil or
solid fuel red appliances remains, the DO or
HTK systems should be used instead.
A stainless steel chimney termination is available for
installations with multi-ue chimneys and a risk of ambers
from wood stoves or similar appliances reaching the top
of the chimney. For details see page 24.
If the chimney is not a straight run, verify that the bend is
accessible for the installation of elbows. If it is
inaccessible, use the UB Flex liner instead of rigid pipe.
Determine the position of the chimney penetration in the
boiler room. Position the hole into the chimney such that
the vent pipe to the boiler adapter runs at a 5/8” pitch per
foot (55mm per meter) to allow condensate to drain into
the boiler reliably. The size of the opening must be
sufcient to install the support rail as shown in Fig. 10.
Drill a 3/8” (10 mm) hole in the rear wall of the chimney at
1-3/8” (35 mm) above the bottom of the chimney
penetration (Fig. 10). Shorten support rail (Fig. 10, Item
1) if necessary and insert the rod into the hole. Lay the
near end onto the bottom of the penetration and ensure it
is level and rigid. After the chimney pipes have been
installed and connections made, it will be mortared in
place.
Place load bearing elbow (Fig. 10, Item 2) in the middle
of the support rail (Item 1) with its guide engaging with
the rail.
Use a rope to determine the exact length between the
gasket of the load bearing elbow and the top of the
chimney.
Proceed to page 18 if you are using rigid pipe, or page 21
for exible liner UB ex.
Fig. 10 load bearing elbow installation
1 Support rail
2 Load bearing elbow

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GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
9.2. Installation of Rigid Chimney Pipe
The rigid pipe is best suited for straight chimney ues
with no offsets, or requires offsets to be accessible for the
installation of elbows. In all other cases use the UB Flex
kit instead.
If additional elbows are needed inside the chimney,
complete the connection between the chimney
penetration and the elbows rst. Coat all gaskets and the
mating pipes with CENTROCERIN® gasket lubricant and
assemble using a slight turning motion.
Before climbing onto the roof, prepare all pipes and
spacers needed for the length of the chimney as
measured in the previous step. Coat all gaskets and
mating pipes with CENTROCERIN® gasket lubricant.
Keep the spacers close by.
Place the two halves of the spacer (Fig.11) around the
pipe and join them together.
The chimney must be thoroughly cleaned before
installing the ue gas system. It is recommended
to use a professional chimney sweep.
Tools needed on the roof
– Vent pipes with spacers attached
– Black or stainless steel top end pipe
– Chimney Cover
– CENTROCERIN®
– Hammer drill with masonry bit 1/4” (6mm)
– 4 wall anchors and screws
– Matching screwdriver
– Tape measure
– Carpet knife or similar
WARNING! RISK OF DEATH FROM FALLING.
Take sufcient measures to prevent accidents on
the roof.
Use state of the art safety equipment and take
common sense safety measures.
WARNING! RISK OF INJURY OR DEATH FROM
TOOLS AND EQUIPMENT FALLING FROM THE
ROOF.
Secure tools and equipment against falling from
the roof.
Fig. 11 Spacer
Insert ue gas pipes with the gasket facing up and
equipped with spacer (Fig. 12 Item 1) from above into the
chimney (Fig. 12, Item 2), until the pipe sleeve is a little
above the upper edge of the chimney. Take the next ue
gas pipe and join them together by turning slightly.
Fig. 12 GAK chimney installation

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05.2009 Technical specications are subject to change without prior notice
Lower ue gas pipes further into the chimney and repeat
the procedure for all other pipes until reaching the
support elbow.
Have a second person make the connection with the
support elbow at the base of the chimney by slightly
turning the pipe into the gasket. Push down from the top
to ensure a secure connection.
If installing the stainless steel chimney cover, proceed to
page 24.
For the black chimney cover, only the black pipe is UV
proof and may be exposed to the elements above the
roof. Adjust the length of the last white pipe so that the
terminating black pipe extends at least 13” (330mm)
above the top of the chimney where the cover will be
attached. This will result in a minimum of 3” (75mm)
clearance of the pipe above the cap.
Remove the top of the chimney cover (Fig. 13, Item 1) by
pulling it up. Ensure it is held by its leash. Push the cover
over the terminating black pipe and verify that it ts the
top of the chimney. The base can be trimmed to match
the chimney crown by cutting along the lines shown in
Fig. 14, Item 1.
Set cover on the top of the chimney and mark 4 holes.
Drill holes and insert wall anchors. Caulk around the
perimeter of the cover to prevent rain water from entering
the chimney and screw down rmly. Push upper part of
the chimney cover over the ue gas pipe and press down
until it snaps in place.
Fig. 13 Chimney cover
1 Chimney cover
Fig. 14 Base of chimney cover
1 Lines indicating where cover base can be cut to size.

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GB125 Concentric Vent
Design Manual
GB125 Concentric Vent Design Manual | 05 .2009
Technical specications are subject to change without prior notice
Chimney connection
The elbow and rail support the weight of the vent pipe
inside the chimney. Ensure both are installed properly
and provide support.
Shorten the penetrating pipe and ue gas pipe so it
extends approx. 2” (50 mm) beyond the face of the
chimney (Fig. 15). Carefully remove the burrs from cut
edges.
Coat the gasket (Fig. 15, Item 2) of the concentric wall
penetration and the mating pipe of the support elbow with
CENTROCERIN® and assemble using a slight turning
motion. Allow a 5/8” pitch per foot (55mm per meter)
toward the boiler. Mortar the penetrating pipe in place.
Slide on the face plate (Fig. 15, Item 1), and once the
mortar has cured, mark and drill mounting holes, insert
wall anchors, and screw on the face plate.
Connection to the boiler
Connect the inspection and clean-out pipe to the boiler
adapter. Measure the remaining distance to the chimney
penetration and complete the connection with concentric
pipe as described in chapter 5.6.
Ensure a 5/8” pitch per foot (55mm per meter) toward the
boiler (Fig. 16).
For more details consult the GAK installation manual.
Fig. 15 Chimney connection
1 Face plate
2 Gasket in chimney penetration
Fig. 16 Boiler connection