Which glycol concentration do you need? 30%, 40%, 50% or 100% explained
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- By Huchem UK
Huchem supplies glycol as pure 100% and as ready mixed 30%, 40% and 50% solutions. Each concentration gives a different level of frost protection. This guide helps you pick the right one for your installation and explains why more glycol is not always better.
Glycol lowers the freezing point of the water in your heating or cooling system. How far it lowers it depends on the concentration. Huchem supplies ethylene glycol and propylene glycol in four versions: 100% pure glycol and ready to use mixtures of 30%, 40% and 50%. Which one do you need?
Frost protection per concentration
As a guide, these are the approximate temperatures at which each mixture is protected against freezing:
- 30% glycol: protection down to around -13 °C (propylene) to -15 °C (ethylene). Suitable for most UK outdoor installations, dry coolers, heat pumps and solar thermal systems in sheltered locations.
- 40% glycol: protection down to around -21 °C. The safe all round choice for exposed outdoor pipework, roof mounted units and cold store applications.
- 50% glycol: protection down to around -33 °C. For low temperature process cooling, freezer applications and installations where the fluid itself is chilled well below zero.
- 100% glycol: pure, undiluted glycol for mixing on site with demineralised water, or for topping up an existing system to raise the concentration.
Note that frost protection and burst protection are two different things. Below the frost protection temperature the fluid turns into a slush, which stops flow but does not yet expand enough to burst pipes. Burst protection generally extends a further 10 to 15 degrees lower.
More glycol is not always better
It is tempting to fill with 50% and be done with it, but a higher concentration comes at a price. Glycol has a lower heat capacity than water and a higher viscosity. The more glycol you use, the less heat the fluid can carry and the harder the pumps have to work. In a cooling system this means reduced capacity and higher energy consumption. Choose the lowest concentration that gives you a safe margin below the lowest temperature the system will see. For most UK applications that is 30% or 40%.
Ready mixed or mix it yourself?
Ready mixed glycol is mixed with demineralised water in the factory, so the ratio and the inhibitor dose are exactly right and you can fill straight from the can. If you mix on site from 100% glycol, always use demineralised water. Tap water contains minerals and salts that cause scale and corrosion and reduce the effectiveness of the inhibitors. Measure the final concentration with a refractometer.
Do not forget the inhibitors
Pure glycol on its own does not protect against corrosion. Over time it can even become slightly acidic. All Huchem glycol mixtures contain a high quality inhibitor package that protects steel, copper, brass and aluminium and inhibits the growth of bacteria and algae. This extends the life of pumps, pipework and heat exchangers considerably.
Ethylene or propylene?
All four concentrations are available as ethylene glycol and as propylene glycol. Ethylene glycol has the best heat transfer properties and is the standard for industrial cooling. Propylene glycol is the safe choice wherever the fluid could come into contact with food, drink or people. Read our article Ethylene glycol or propylene glycol: which one should you choose? for the full comparison.
Checking an existing system
Glycol does not evaporate, but a system that has been topped up with plain water over the years will gradually lose its frost protection. Test the concentration every autumn with a refractometer and top up with 100% glycol if needed. If the fluid looks dark, smells sour or contains sludge, it is time to flush the system and refill.
Need help choosing? Send us the type of installation, the system volume and the frost protection you need, and we will recommend the right product.