Anti-freeze valves and glycol are two different components that serve similar purposes in a heat pump system. Glycol is a type of anti-freeze that is commonly used in heat pump systems to prevent water from freezing in cold weather. Glycol is specifically designed to lower the freezing point of water, which is necessary to prevent damage to the system in cold conditions. Anti-freeze valves, on the other hand, are designed to automatically open and drain out the water within the system when the water drops below a certain temperature. This is also to protect the system from cold weather.
Disadvantages of Glycol
Most heat pump installers will be familiar with glycol and if you’ve ever worked with us, we’ve probably recommended glycol to you. That said, there are a few downsides to using it:
Cost: Glycol is expensive and generally, multiple tubs are needed to fill a heat pump system correctly. Typically, it costs around £200 for a 20l container of glycol, so using multiple tubs in a heat pump system increases the overall cost.
Maintenance: Glycol requires regular testing and replacement to ensure that it is functioning properly. If you need to drain down the system, the glycol will need to be replaced which ultimately increases the cost.
Performance: Glycol is a gloopy, viscous liquid which, even when mixed with water, can reduce the efficiency of a heat pump. Adding glycol to the system will mean the heat pump needs to work harder to move the liquid through the system. Water, on the other hand, is very fluid which is preferable in a heat pump system.
Toxicity: Glycol is toxic if ingested, so care must be taken when draining down the system.
What at are the Benefits of Anti-Freeze Valves?
Anti-freeze valves are designed to drain down a heat pump system if the temperature of the heating circuit (not the outdoor temperature) drops below 3°C degrees. Each valve contains a small sensor that triggers when the heating circuit falls below this temperature. The system would have to lose power (and the pumps stop running) or we would have to enter a new ice age for this to happen. Similarly to glycol, this is done to prevent the heating system from being damaged in cold conditions. Here are the benefits to using anti-freeze valves:
Cost: For a pair of anti-freeze valves, the cost is comparable to that of a 20l tub of glycol (£200) however, only one pair is needed.
Maintenance: The valves are a fit and forget product, requiring no maintenance and should still be working in 7-8 years.
Performance: Anti-freeze valves serve as an alternative to glycol which means your heat pump system will work more efficiently due to the fluidity of the water.
To find out more, we’ve put together a short video to explain the benefits:
What about the heat pump warranty?
Many installers will be concerned about the possibility of invalidating a heat pump warranty by using anti-freeze valves. Thankfully, this is not the case. Most manufacturers state, ‘there must be anti-freeze protection’ and do not list glycol as the be all, end all. In fact, Bosch specifically state NOT to use glycol.
In the case of Mitsubishi, here’s their stance on anti-freeze valves:
“Anti-freeze valves can be used, but you must ensure the freeze stat function on the FTC6 is enabled.”
The Mitsubishi Ecodan has a function whereby when the outdoor temperature gets below 5 degrees, it runs the pumps to ensure water doesn't freeze. So anti-freeze valves are supported by Mitsubishi when that function is used (which it always is).
Can you Use both?
Some installers have asked about the possibility of using both anti-freeze valves and glycol for extra protection. This is not something we recommend. Mechanically, the system would work without a hitch, however, it would be a complete waste of money for your customer and wouldn’t add any value.
Adding glycol to the system would reduce the freezing point of the water in the system, however, it would not change the temperature at which the anti-freeze valves open. Therefore, if the valves were triggered, the system would be drained meaning you would waste all the glycol.
Stock Available
We now hold stock of anti-freeze valves and are recommending them to our installers. To find out more, get in touch or download the spec sheet below:
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