PEX tubing has a reputation of being very resilient when it comes to cold temperatures. As the water starts to freeze, the tubing expands, thus minimizing the chance of it bursting. However, the expandable qualities of PEX are less likely to protect it from prolonged sub-freezing weather and as water in the system turns into ice and takes up more volume, it has a chance of bursting, causing significant damage not only to the system itself but also to the property its installed in.
In order to prevent water in PEX tubing from freezing in a closed loop radiant heating or snow melt systems, it can be mixed with anti-freeze. Anti-freeze is a liquid consisting of chemicals that when added to water reduce its freezing point. There are two major types of anti-freeze. Propylene Glycol and Ethylene Glycol. Propylene Glycol is non-toxic and is commonly used as anti-freeze in hydronic heating systems. Ethylene Glycol is toxic and is used mainly for automotives and is not to be used in hydronic systems.
When anti-freeze is added to the system, back flow preventer needs to be in place to ensure that water in the heating system does not mix with potable water. The amount of Glycol that needs to be added varies depending on expected temperatures, and amount of anti-freeze to water ratio can vary from 20% to 50%
Though anti-freeze allows tubing to survive freezing temperatures, it does have certain drawbacks in the form of lower heat transfer rate and increased energy load on the circulator pump.
Since introducing glycol into the system will reduce the heat transfer rate, more hot water would need to be pumped to maintain target temperature. Moreover, anti-freeze is thicker than water, therefore more pressure will be required to circulate it