A Glycol Primer and FAQ

A Glycol Primer and FAQ

Polypropylene glycol can be an essential part of your in-floor heating system. However, here are a few things to consider before you add any to your system. 

What exactly is glycol? - Glycol can come in different forms, but we’re going to focus on propylene glycol (P-Glycol). It is a liquid compound that is used as an antifreeze agent primarily in hydronic heating systems. It is usually colorless and odorless. P-Glycol is effective at lowering the freezing point of water and helps provide protection in cold environments. Examples of utilization would be hydronic systems used for heating cabins, out-buildings, and snow-melt installations. In other words, you should use it where you have freezing concerns of your in-floor heating systems. 

What are the other forms of glycol and can I use them in my hydronic heating system? - One of the other antifreezes that you will see is something called ethylene glycol (E-Glycol) and it is mostly used in automotive applications. It is odorless, is often dyed pink, and is said to taste sweet. It performs better as a heat-transfer and it usually can be less expensive than P-Glycol. However, E-Glycol is extremely toxic. In fact it is more toxic than P-Glycol and that is one of the main reasons P-Glycol is preferred in hydronic heating systems. 

How much glycol should I use? - Determining the proper amount of P-Glycol to use is dependent on how low you think the temperature will get. However, the most common concentration is 1:1 mixture or 50% water to 50% P-Glycol. This will protect your in-floor heating system from freezing down to -22F (-30C), which should be plenty of coverage. The important thing to remember is that, yes, you can add more P-Glycol to your system to add to its protection ability. However, as you increase the concentration of P-Glycol to your system, you will decrease the efficiency of heat transferability. Pure distilled water is recommended for a peak heat transfer rate. Any additions of P-Glycol only diminish that rate. Moreover, as you increase the concentration of P-Glycol to your system, you are also adding protection from biological growth. A safe concentration would be at 25% or a 4:1 water to P-Glycol ratio. On a side note: there are brands that are premixed at a 60% glycol ratio. If you followed the 1:1 ratio with that mixture, you would end up with a 30% glycol concentration, still above the biological growth threshold and will still offer freeze protection to -18F.
In the end, be sure to follow the mixing ratios on the spec sheet of your preferred glycol. 

How often should I exchange my glycol? - There are many different types of glycol and their use-life is varied. However, the rule of thumb is to exchange any glycol in your in-floor heating system every 5-7 years. Simple test strips can be purchased at local hardware stores or online that can test the level of freeze protection and the level of corrosion protection still in the system. Additionally, perform pH checks quarterly. A rule of thumb for pH levels is 8-8.5, but you will need to consult your boiler system to make sure you are within proper limits. 

What is the freeze limit? -  When doing research, you may find the term “freeze limit,” “pumpable limit,” or “burst protection limit.” Let’s go over what these limits mean.” First off, “freeze limit” is the temperature where no ice crystals will form and the fluid remains liquid. “Pumpable limit” is the temperature where a flowable liquid slush may begin to form, but depending on the pumps used, they will still be able to move this fluid through your system. Lastly, “burst protection limit” accounts for temperatures well below the freeze limit at which the liquid becomes too frozen to move through the system. At this level, damage can happen to your system. 

How do I clean the glycol out of my system? - After a few seasons, you may find that the glycol isn’t working as it should. Glycol has a tendency to degrade over time, so do not be surprised when you have to remove and properly dispose of it. When you decide to replace your glycol, it is very important to dispose of it properly. Do not drain your used glycol down the drain. Instead, find a local company that handles antifreeze and call them to take it away. It may even be recycled! 

Glycol FAQs - Let’s get through some rapid-fire frequently asked questions:

Can I use bleach or chlorine to clean my system? - You may be tempted to use bleach or chlorine to clean out your system. Never use bleach or chlorine in your system! It will corrode any metal in your system. Additionally, mixing bleach with hot water may cause chlorine gas which is extremely poisonous. Additionally, using chlorine in your system will cause a violent and dangerous reaction. Let’s be clear: DO NOT PUT CHLORINE OR BLEACH IN YOUR SYSTEM. The glycol will mix with each substance, causing damage to your system and harm to you. 
How long is the shelf-life of glycol? - If you need to store your glycol before use, you can count on around two years of stability. However, if you have an inhibited glycol, you can expect an indefinite shelf life if stored at an ambient temperature.
Who invented glycol? - P-Glycol was invented by Charles-Adolphe Wurtz as an alternative to E-Glycol in 1859.

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