A word of caution: pure glycol contains no corrosion inhibitors. Using this kind of product in aqueous solution may cause severe corrosion to your circuits.
Even if the pipes are made of stainless steel, if you have a different alloy somewhere in the system (eg copper in a heat exchanger), you will have galvanic coupling and we do not know in this case which allow will act as the shield to the other.
We recommend using treated water (demineralised) in order to limit the introduction of compounds (chlorides, sulphates, carbonates) that can jeopardise corrosion resistance. All the standardised corrosion tests are carried out with concentrations of 33% by volume of anti-freeze. Below this concentration, the amount of corrosion inhibitor in the circuit is too low and may not provide adequate protection against corrosion.
That is why we recommend, not just because of the protection provided against freezing, using a minimum concentration of 33% by volume of anti-freeze. This concentration, depending on the anti-freeze gives freezing point of 12 - 18C.