At the end of this winters` heating season I plan to give my system a flush clean and refill with fresh glycol. At the moment it is filled with propylene glycol but I was thinking of replacing it with non-toxic ethylene glycol to take advantage of the better physical properties. But my interweb trawl found this ….
The non-toxic ethylene glycol has only been tested on rats.
The mechanism for blocking the toxic metabolic pathway has not been proved.
Now, I assume toxicity testing on many substances is performed on rats rather than humans, so not sure about that objection. However, my fifty year old Chemistry A Level is totally inadequate to form an opinion on the second objection. Any Biochemists out there who might be able to give a more informed opinion?
As background, I found the patent concerning how to make non-toxic ethylene glycol …….
It seems that the process is simple, just add 5% propylene glycol or glycerol. If ingested the additives are metabolised to benign products in preference to metabolising the ethylene glycol giving time for the ethylene glycol to be lost by excretion.
Hello @toadhall have you considered flush and refill without glycol? E.g using an anti-freeze valve or is your location particularly cold and at risk of power cuts?
Small, but since it is time for a flush and refill and the detox ethylene glycol is a similar price to propylene glycol so if there was no down side then the ethylene glycol is an improvement.
I am not sure if the risk is somewhat exaggerated. I have the worst system from a risk point of view, a vented DHW system and pressurised CH system. So if the coil in the DHW tank leaks then the entire contents of the CH expansion tank is going to vent into the DHW. The possibility exists of it being pushed into the cold water tank as well. But it is going to be significantly diluted and we generally don`t drink the DHW or cold water from the tank. I guess there is a set of circumstances where we could end up drinking it, so the coil bursts AND there is a water cut at the same time. Hence my question, if it works, would the detox ethylene glycol mitigate this small risk.
Maybe I am cursed, but things seem to go wrong when I am away from home in the winter. We are out in the sticks and near the East Coast, but certainly not in the highlands of Scotland. I prefer glycol to anti-freeze valves.
Anti-freeze valves are mechanical so prone to failure. I have seen a few reported instances where the valve has opened prematurely and dumped the CH contents with people returning to no heating and having to fiddle about in the cold and dark to refill the system. We are too old to suffer that.
Glycol makes the system intrinsically freeze proof, the only inconvenience being to test the concentration once a year, and top up as necessary. I can cope with that.
Thanks for your thoughts, gives me stuff to mull over before coming to a conclusion later this year.
In your situation, I’d find an installer who’s willing to fill your system with water treated to VDI 2035, and ditch glycol altogether. The frost damage risk is low, and potable contamination risk seems to be higher, based on what you’ve written.
I would not want anti freeze values if meaningful risk of electricity cuts lasting more then a few hours and noone at the property to refill heating system.
Fair enough! I agree some form of protection is needed and agreed that anti-freeze valves dumping the system is not ideal! I think the ideal is some form of battery backup on the central heating pump but that doesn’t seem to be a common solution yet!