Boiler Quality And Maintenance; Boiler Water Chemistry; Reaction Of Metals To Water Chemistry; Scale And Corrosion - Watts AERCO Modulex EXT Series Technical Application Manual

Modulex EXT Series Piping

BOILER QUALITY AND MAINTENANCE

SECTION 2: BOILER QUALITY AND MAINTENANCE

2.1. BOILER WATER CHEMISTRY

2.1.1. Reaction of Metals to Water Chemistry

A neutral water pH must be maintained because, although the aluminum alloys used in the construction of
Modulex EXT boilers resist acidic conditions, they are still vulnerable to highly alkaline environments (pH of
9.0 and above). THE WATERSIDE pH MUST BE MAINTAINED BETWEEN 6.5 and 8.0.
Metals such as aluminum, steel, iron, and copper used in hydronic heating systems are highly reactive to
acidic and alkaline environments; the water must be treated with protectants and buffers to prevent
corrosion. Most chemical water treatments have been developed to protect an array of metals.

2.1.2. Scale and Corrosion

Free oxygen can cause the formation of rust (iron oxides), which degrade metallic materials. Magnetite is
formed in un-inhibited water if there is electrolytic action in the presence of oxygen. Sludge is formed when
calcium compounds, primarily CaCO3, are heated. Rust and magnetite, when combined with sludge, can
form a very hard scale, which significantly reduces system efficiency and life expectancy of the heating
system. Scale reduces heat exchange due to its low heat conductivity and so may cause very dangerous
localized overheating. Waterside corrosion of all heating circuit surfaces is also a major concern.

2.1.3. Make-up or Feed Water Quality

Make-up or feed water is water added to a closed hydronic system to replenish water lost through
evaporation, maintenance, or leakage. The quality of make-up or feed water, which may contain dissolved
oxygen, minerals and other dissolved contaminants, is extremely important. Such introduced water must
be chemically treated or strictly limited when ensuring neutral chemical conditions in boiler system water.
Generally, any closed hydronic heating system should be restricted from receiving untreated makeup water
of no more than 5% of the total volume of system water per year. Reverse osmosis, deionized, distilled or
mineral treated water should not be used.

2.1.4. Treating Water to Prevent Freezing

When using anti-freeze solutions, their compatibility with the AERCO Modulex aluminum heat exchanger
and other components of the heating system must be determined prior to use. TRADITIONAL HVAC
PROPYLENE GLYCOL IS NOT SUITABLE FOR ALUMINUM HEAT EXCHANGERS: the pH of glycol at
various dilutions is in excess of 9.5, whereas the pH must be within 6.5 and 8.0 for use with
aluminum. There are several suitable aluminum safe propylene glycols available that can provide the
same levels of burst, freeze and corrosion inhibiting protection as traditional propylene glycols. Consult
Section 2.3 for recommendations on glycol solutions. If a glycol solution is used as anti-freeze protection, a
backflow preventer must be installed upstream of the fill/makeup valve.
Only virgin glycol should be used for systems requiring freeze protection, and it must be treated with an
inhibitor compatible with the particular chemical treatment being used in the system. Note that glycol must
be changed from time to time due to its limited useful life.

2.1.5. Water Treatment Certification

When using chemical treatments in hydronic systems, it is necessary to ensure that the chosen treatment
is appropriate and certified by the manufacturer for such environments. The manufacturer should also
guarantee that the treatment, when applied according to the manufacturer's recommendations, will not
TAG-0099
Application Guide
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, NY 10913
Phone: 800-526-0288
Page 5 of 37
10.07.2021