Heat Transfer Fluids for Bored Geothermal Heat Exchangers
Well Management Program
Minnesota Rules, part 4725.7050 requires that only food-grade or United States Pharmacopeia (USP)‑grade propylene glycol may be used as heat transfer fluid in a bored geothermal heat exchanger. No other materials or additives may be used except potable water.
Some propylene glycol products contain small amounts of other chemicals to stabilize or prevent corrosion. The Minnesota Department of Health (MDH) has determined that some of these products meet the intent of the rule. Upon request from a manufacturer, the MDH will review product information for an inhibited propylene glycol to determine if it is safe and acceptable for use in a bored geothermal heat exchanger. Approval of an inhibited propylene glycol is based on manufacturer submission to MDH of documentation identifying the additives/inhibitors and verifying that all ingredients are food grade or USP grade, and listing of the product in the NSF White Book™ listing for nonfood compounds.
Propylene glycol with additives must not be used in a bored geothermal heat exchanger unless the MDH has provided written approval for that specific product.
The MDH has prepared the following list of approved inhibited propylene glycols for use in bored geothermal heat exchangers:
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Contact the MDH Well Management Section
651-201-4600 or 800-383-9808
Minnesota Department of Health