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Glycol is well known for providing excellent freeze protection for closed-loop, water-based (hydronic) HVAC heating and cooling systems. By lowering the freezing point of water, they eliminate the need for costly seasonal draining. However, not all glycols are created equal. Some work harder, providing additional protections for your system. This means that the type of heat transfer fluid you select will impact the system's overall performance and longevity.
What is Uninhibited Glycol?
Uninhibited glycol (or plain glycol) provides freeze and burst protection at a relatively low initial cost. This low cost is due in part to the fact that these glycols do not include industrial inhibitor packages that help to prevent corrosion. Corrosion (aggravated by heat, oxygen, chlorides, sulfates, metal impurities and other contaminants) can cause severe damage to your system leading to unscheduled shutdowns, high maintenance fees and even reduced system life.
Not only do uninhibited glycols leave your system vulnerable to corrosion, they can also accelerate the problem. Since glycols produce organic acids as they degrade, especially when heated, these acids when left in the system will lower the fluids pH. With no corrosion inhibitors to buffer these acids, the corrosion rate of a solution of uninhibited glycol can be greater than that of plain water (which is highly corrosive).
For these reasons, we do not recommend uninhibited glycols be used for HVAC heat transfer.
What is Inhibited Glycol? Why Choose Inhibited Glycol?
The proprietary industrial inhibitor packages used in DOWTHERM™ SR-1 ethylene glycol and DOWFROST™ and DOWFROST™ HD propylene glycol are specially formulated to help prevent corrosion in two ways. First, the corrosion inhibitor "passivates" metal surfaces, so they are less susceptible to corrosion. Second, they buffer the organic acids formed as a result of glycol oxidation to keep the fluid from becoming acidic. Dow® heat transfer fluid provides corrosion protection without reducing heat transfer efficiency caused by fouling.
The below table illustrates the comparative corrosion effects that inhibited and uninhibited glycols and plain water may have on metals commonly found in HVAC applications.