PR2: 03/01/13 Page 6of 38
Technical Application Guide
AERCO International, Inc. •100 Oritani Dr. •Blauvelt, New York 10913 •Phone: 800-526-0288
1BOILER WATER QUALITY AND MAINTENANCE
1.1 Modulex Boiler Water Chemistry
1.1.1 - Reaction of Metals to Water Chemistry
Acidic condensates with a pH of 3.0 to 5.0 are commonly produced by the burning of natural gasses
within hydronic heating systems. It is very important to maintain a neutral chemistry of the water
because although the aluminum alloys used in the construction of Modulex boilers resist acidic
conditions, they are still vulnerable to highly alkaline environments (pH of 9.0 and above).
Metals, including aluminum, steel, iron, and copper used in hydronic heating systems are highly
reactive to acidic and alkaline chemical environments, so the water must be treated with protectants
and buffers to prevent corrosion of these metals. Because of this, most chemical water treatments
have been developed to protect an array of metals.
1.1.2 - Scale and Corrosion
Free oxygen can cause the formation of rust (iron oxides), which degrades 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.
1.1.3 - 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.
1.1.4 - 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 the 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 your local
AERCO representative 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.
1.1.5 - 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 cause harm to the boiler, pumps, piping, and other components of the
hydronic boiler system.
