Primary Loop Plumbing; Multiple Boiler Primary Loop Plumbing; Secondary Loop Plumbing - Smith GT-150 Installation, Operating And Maintenance Manual

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Hot water boilers are designed to operate with airless
water in the system. The GT boiler is provided with
a 1/8 in, 3 mm, air vent located on the top of the unit.
This air vent is intended to vent the boiler on initial
startup. This device will NOT continuously vent air
collecting in the primary loop and is not intended
to be the primary venting device. The air scoop as
shown in Figure 21 is the primary venting location. It is
recommended that an additional air scoop be used in
the secondary plumbing. If air continues to be a problem
an air scrubber must be used.
NOTE: Only inhibited propylene glycol solutions
should be used if freeze protection is required.
Avoid using mixtures greater than 30%, unless
the size of the boilers' circulator(s) is increased
accordingly. Under no circumstances should a 50%
mixture be exceeded.
Low Water Cut Off, LWCO
If a LWCO is used ensure that the water line of the "Low
Water Cutoff" is at least 6 in, 152 mm, above the top of the
boiler, Figure 21. It is recommended that the LWCO be
situated so that it can be tested without removing water
from the boiler. Tri-cocks and a gauge glass are highly
recommended. Valves shall not be installed between
the LWCO and the boiler. Use an air vent if installed as
per our diagram to be used as a vacuum breaker and to
eliminate air upon fi lling.
Figure 21 - LWCO & Air Vent Piping
Table 3 - Recommended Primary and Indirect Loop Circulators
Restriction
Model Head Loss
GT150 7 ft at 6 GPM, 2.1 m at 0.4 L/s
GT200 10 ft at 8 GPM, 3 m at 0.5 L/s
GT INSTALLATION AND OPERATION INSTRUCTIONS
Minimum
Flow
GPM, L/s
6, 0.4
8, 0.5

PRIMARY LOOP PLUMBING

This low mass boiler requires a continuous minimum
water fl ow for proper operation. The heat exchanger in
this boiler is more restrictive than a conventional boiler.
The system pump must be sized to overcome the head
loss of the boiler, Figure 22. Greater consideration must
be given to the capabilities of the circulating pump(s) in
the primary-loop. This includes the pump used for an
indirect tank.
Figure 22 - Boiler Head Loss
Table 3 lists the recommended circulators for use as the
primary and indirect loop pumps.
Figure 23 shows the proper way to plumb a primary loop
for single boiler installations.
MULTIPLE BOILER PRIMARY LOOP
Figure 24 shows the proper way to plumb a primary loop
for multiple boiler installations.

SECONDARY LOOP PLUMBING

Figures 25 and 26 show some typical primary/ secondary
piping systems. It is the responsibility of the installing
contractor to determine which system best meets the
need of the installation. Contractor modifi cations to these
instructions may be required, based upon the existing
piping and system design.
Max. Temp.
Rise
°F, °C
B&G
45, 25 NRF-33
45, 25 PL-36
Minimum Primary &
Indirect Pump Size
Grundfos Taco
UP 26-64 0010
UP 26-99 0011