ASHP glycol

[Jeremy Harris]

Last time I looked at the specs for heating inhibitors, none used organics, most used sodium nitrite or similar.  I do know that there were some issues with silicate inhibitors, but that applies to some automotive and aviation engine cooling systems as well (one aircraft I owned years ago had a system that wasn't compatible with either silicate or organic acid based inhibitors, only nitrite and phosphate based ones).  Not 100% sure why you can't use one of the newer inhibitor compounds in a heating system, as I can't see any obvious reason why they shouldn't be compatible with all the materials within a heating system.  Might just be that the manufacturers of boilers etc don't want the added cost of testing for compatibility, as the life of the inhibitor isn't a selling point for a boiler, whereas is is for cars, where servicing costs play a big part in fleet buying decision.

 

Worth bearing in mind that ground source heat pumps usually have to use more expensive  propylene glycol based antifreeze/inhibitor, rather than the cheaper ethylene glycol that's OK for an ASHP, simply because of the toxicity of ethylene glycol if it leaked into the soil from the ground loop, which is the main reason why it costs so much to fill and replace it every 5 years or so.

 

Technically, I can't quite see why just the inhibitor element of the antifreeze couldn't be replaced, as that's the limiting factor in terms of the life of the stuff usually, and what sets the nominal 5 years that most manufacturers seem to recommend.  You can get testers for checking whether the inhibitor within a heating system is still OK, but the sealed jam jar and clean nail test would be as good anything else for showing whether the stuff was still OK, and if it passed that test I'd have no problem with carrying on using it.  I used to do this test every years on our old heating system, when I checked the magnaclean filter.  Admittedly I'd usually top the magnaclean up with a drop of fresh inhibitor every year, but the stuff in our old heating system has been in there about 10 years now and still seem fine.

[dpmiller]

^ unsealed jamjar just in case, don't the inhibitors head acidic after dealing with oxygen?