16
TWT shall not be greater than ninety (90) equivalent feet
[27.4 m] of vent pipe nor less than nine (9) feet [3 m] (excluding
fittings) unless the vent is through a non-combustible wall. A
maximum of three (3) 90° degree elbows may be used. For
standard installations where no air intake piping is included,
the total distance can be extended to 180 equivalent feet
[54.9 m] with a maximum of five (5) 90° degree elbows.
Standard minimum horizontal vent length is three (3) feet
[1.0 m]. See figures 9A and 11 for differences between standard
and direct vent installations.
4. This horizontal exhaust vent system must pitch upward toward
the termination at 1/4 inch per foot (21 mm per meter).
5. The TWT is designed such that the building is protected from
degradation by flue gas and condensate. However, if
additional protection is desired, install against the wall a
non-corrosive metal sheet under the TWT.
6. Due to the normal formation of water vapor in the combustion
process, horizontal terminations must not be located over areas
of pedestrian or vehicular traffic, (i.e., public walkways or over
areas where condensate could create a nuisance or hazard).
This is especially true in colder climates where ice buildup is
likely to occur. A.O. Smith Corporation will not be held liable
for any personal injury or property damage due to any
dislodging of ice.
DIRECT VENT INSTALLATION REQUIREMENTS
Follow the guidelines in the “HORIZONTAL INSTALLATION
REQUIREMENTS” section for the exhausting of flue products.
IMPORTANT
The labels in the Direct Vent Kit must be affixed to the boiler in
locations specified by the instruction sheet provided in the kit.
The following are requirements for the Air-Intake Terminal (AIT):
1. The Air-Intake System (AIS) must terminate with the venting
equipment provided with the boiler, see “DIRECT VENT KIT
PARTS LIST”, part no. 192109.
2. The AIT shall not be located less than three (3) feet [1.0 m]
below any exhaust vent within ten (10) feet [3.0 m], also see
“HORIZONTAL INSTALLATION REQUIREMENTS” section.
3. The total horizontal distance of the AIS from the boiler’s Blower
Adapter to the outside of the “AIT” shall not be greater than
ninety (90) “equivalent” feet [27.4 m] of vent pipe nor less than
three (3) feet [1.0 m] (excluding elbows). A maximum of three
(3) elbows, equivalent to ten (10) feet (3.0 m) of pipe each may
be used.
SYSTEM INSTALLATION
GENERAL
If the system is to be filled with water for testing or other purposes
during cold weather and before actual operation, care must be
taken to prevent a downdraft entering the boiler or freezing air
from contacting the system. Failure to do so may cause the water
in the system to freeze with resulting damage to the system.
Damage due to freezing is not covered by the warranty.
Good practice requires that all heavy piping, etc., be supported.
Figure 12 shows a typical primary, secondary piping method.
This is the preferred piping method for most copper fin tube
boilers. Other piping methods, however, may provide good system
operation. A prime concern when designing heating systems is
the maintenance of proper flow through the unit during boiler
operation. The secondary pump should be sized per the
recommended flow rate of the boiler. (See recommended flow
charts on pages 2 and 3 of this manual.)
A system bypass should be installed as shown in fig. 12 to prevent
boiler circulation starvation when the system zones call for
reduced flow.
This bypass may also be used with multiple boilers manifolded
for reverse-return flow. This system bypass would be installed
from boiler outlet to suction side of pump.
HOT WATER HEATING (HYDRONIC) EQUIPMENT
The following is a brief description of the equipment required for
the installations noted in this manual. All installations must
comply with local code.
1. WATER SUPPLY LINE
These boilers can be used ONLY in a forced circulation hot
water heating system. Since most forced circulation systems
will be of the closed type, install the water supply line as shown
on piping diagram, figure 12.
Fast filling of large pipe, old radiator installations and pressure
purging of series loop systems (where high pressures are
not available) requires bypassing of the pressure reducing
valve.
Generally, pressure purging is not possible with a well pump
system. High point air venting is essential.
If the system is of the open type, a pressure reducing valve will
not be required as the water supply to the system will be
controlled by a manually operated valve. An overhead surge
tank is required. A minimum pressure of 15 psi (100 kPa)
must be maintained on the boiler at all times to ensure
avoidance of potential damage to the boiler which may not be
covered by the warranty.
2. EXPANSION TANK
If the system is of the closed type, install an expansion tank as
shown in figure 12. The sizing of the expansion tank for a
closed system is very important and is directly related to the
total water volume of the system. Refer to “Systems and
Equipment” volume of the ASHRAE handbook.
An air separator as shown in the piping diagrams is
recommended especially for modern commercial hydronic
systems.
3. VENT VALVES
It is recommended that automatic, loose key or screw-driver
type vent valves be installed at each convector or radiator.
4. SYSTEM HEADERS
Split systems with individual supply and return lines from the
boiler room should normally have this piping connected to
supply and return manifold headers near the boiler. To achieve
good water distribution with maximum pressure drop for
several circuits, manifolds should be larger than system
mains.
The circuits should be spaced on the heater at a minimum of
3” (76 mm) center to center. Install a balancing cock in each
return line.
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