Why do I need Glycol?
by Energie Solutions | Mar 25, 2026 | Technical Guides
This conversation topic is one of the host perennial discussions within the heatpump industry.
As the lead technical engineer of Energie Solutions not only do I have my own option, but I have also attended numerous manufacturer training courses and trawled through even more Manufacturers Instructions manuals. The result being … confusion!!
If we start at the beginning……
The underlying issue stems from the fact that with a Monobloc ASHP, the water being used to heat the hot water cylinder, radiators and Underfloor heating is travelling outside to the unit to get heated.
This leaves it exposed to potential sub-zero temperatures which “could” be cold enough to freeze the water inside the unit – and from personal experience I have seen this happen.
However, based on sub-zero temperatures outside it is more than reasonable to expect the heating will be operational inside; keeping you warm in the cold weather. This means that the water is moving around the system and is more than likely 35-40 degrees+ to freeze the water in this situation would need some external temperatures far, far in excess of the average UK temperatures – all good
In addition to this, manufacturers such as NIBE, Daikin, Stiebel Eltron, Mitsubishi to name a few, have protocols to stop the system from freezing by using a combination of running the pump and/or compressor at certain ambient temperatures.
HOWEVER
The colder the temperatures get outside, the harder the heatpump works – greater chance of the unit breaking down – no power – no pumps – no compressor – no heat
In rural areas, the colder the temperatures get, the greater the chance of a power cut – no power – no pumps – no compressor – no heat
Is it all Just about the freezing?
No, a good quality “Glycol” or more technically correct – heat transfer fluid is a 3-in-1 fluid that is not only glycol based for freeze protection but will also have inhibitor and biocide additives as well, to maintain the water quality of the heating system
Good system water quality is slowly becoming the manufacturers non-comital go-to answer to appeasing the installation community around not only the issue of glycol whilst ignoring the failings of anti-freeze valves but also the installation of strainers and magnetic filters
Whats does all this mean?
One thing is clear, there is no single answer.
I recently published an article in Mars Mlodzinski’s book “The Ultimate Guide To Heat Pumps” talking about these very topics and how personally disappointed I am that there is little guidance from Industry Regulators or Manufacturers. What we are left with is everyone’s opinions that have a bias to one angle or another – mine included.
Once thing is indisputable – If we look purely at the “freezing” aspect the risk is relatively low especially in some UK regions. However, there is still a risk however small, and when compared against the cost of a replacement unit the argument for glycol is compelling – its not a problem until it is a big problem.
