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P/N 42-9470 11/07 Copyright 2007 Mestek, Inc.
Cast iron condensing boiler
Cast iron condensing boiler
— Installation and operation manual
Fill and test the system
(continued)
Antifreeze
Antifreeze for hydronic systems contains propylene glycol and an inhibitor. With-
out the inhibitor the glycol is actually corrosive. So the system water must be
checked at least annually to ensure that the inhibitor is at the correct level .
Never
use galvanized piping in a system that contains antifreeze. Never use chromate
water treatment. Either of these will react with the inhibitor in the antifreeze mix.
Antifreeze concentration
— If not using a pre-mixed antifreeze solution, de-
termine the amount of antifreeze to add based on the total volume of the system
piping, the boiler and the expansion tank. Follow the antifreeze manufacturer’s
instructions for the ratio of glycol required for the lowest expected exposure tem-
perature. NEVER use a glycol mix greater than 50%.
Prevent leaks
— Glycol will escape more easily than water through any leak in
the system. So the glycol concentration will reduce if a leak is allowed to continue.
Eliminate all leaks in the system and have the owner frequently inspect the visible
portions of the system for leaks periodically. Do not use circulators or valves with
packing glands, the packing glands can weep.
Install a water meter
— Because the system must be installed with automatic
water make-up to ensure pressure will always be at least 12 psig, you should install
a water meter with one half-gallon resolution on the make-up water line. Th is will
allow monitoring to see if excessive make-up water is entering the system.
Circulator sizing
— Glycol/water mixtures do not move heat as well as water
only. Th e circulator size must be increased to account for this. As a rule of thumb,
increase the fl ow rate by 15%. Assume a 10% reduction in pressure drop compared
to water only at a give fl ow rate.
Constant circulation
— For areas of the system that will be exposed to low tem-
peratures, use continuous circulation to keep the water moving in the pipes.
Expansion tank sizing
— Increase the expansion tank size about 20% to account
for the eff ects of the antifreeze.
Indirect heat exchangers
— Output from indirect heat exchangers (including
indirect water heaters) can drop substantially when using antifreeze/water. Make
sure the exchanger is sized correctly for the application.
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System pressure
Once the system is cleaned, fi lled, purged and treated as
required, set the make-up water pressure reducing valve
to the correct cold-fi ll pressure. Th is is usually 12 psig for
systems using 30 psig relief valves. For higher pressure sys-
tems, set the cold-fi ll pressure such that the system pressure
will never exceed about 80% of the boiler relief valve sett ing
when system water temperature reaches the maximum op-
erating temperature that the system and boiler temperature
controls will allow.
Th e pressure in the boiler must never be below
12 psig. Lower pressure could allow localized
boiling in the boiler heat exchanger, causing
possible damage and section failure.
At cold fi ll, the water level in closed-type expansion tanks
should not be above center. Use the tank fi tt ing to verify
tank water level is correct.
As the system heats up, the water will expand, causing the
system pressure to increase. If the expansion tank is properly
sized and installed, the system pressure will never exceed
about 80% of the relief valve set pressure (24 psig for typical
residential systems).
If the system operating pressure becomes too high, check the
expansion tank to ensure it is large enough. For closed-type
expansion tanks, make sure there are no leaks in the piping
or the tank and the tank fi tt ing is correctly installed. For dia-
phragm or bladder-type tanks, you may have to remove the
tank from the system and verify that it can hold pressure. If it
cannot hold pressure, the membrane may be damaged.
If the system pressure is allowed to rise too high,
the boiler relief valve will open, allowing water to
escape from the system. Th e resultant addition of
make-up water will cause mineral deposits and
oxygen corrosion in the boiler.
Final checks
Aft er the system is cleaned, fi lled and purged, and the system
pressure is correctly set, make sure the water chemistry is
correct. Th e pH and chemistry must be as required (and
specifi ed by the chemical treatment specialist when required).
Make sure all valves are correctly set. Isolation and fi ll valves
should be open before start-up. Purge valves must be closed.
Open the valve on each automatic vent in the system about
one quarter turn to allow venting.
Th oroughly inspect the system for leaks or weeping valves.
Eliminate all system leaks to prevent excessive
make-up water, which introduces oxygen as well
as lime-forming minerals. Th is can lead to heat
exchanger damage, resulting in possible severe
personal injury, death or substantial property
damage.
Watch the boiler pressure/temperature gauge throughout
the start-up process. Make sure the pressure never drops
below 12 psig and never goes higher than 80% of the boiler
relief valve sett ing pressure.
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Use only antifreeze sold for use in hydronic systems
— Never use automotive antifreeze. Automotive antifreeze
and ethylene glycol are toxic to humans and animals and will
damage rubber components in the system.
Make sure the owner is aware that the antifreeze must be
checked periodically by a qualifi ed technician to ensure
the concentration is correct and that the inhibitor level is
adequate.
Obtain the MSDS for the antifreeze and leave a copy with
the owner. Follow antifreeze manufacturer’s guidelines for
application and maintenance.
Failure to follow these guidelines could result in system or
boiler failure, causing possible severe personal injury, death or
substantial property damage.
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