The Glycol Myth Why your pipes may freeze anyway

This topic always throws me for a loop when a customer brings it up because I don't know how to answer definitively. I always test existing systems and flush and/or add accordingly to bring everything back up to spec, but occasionally when they ask why/how (usually referencing how the antifreeze in their car is 20-30 years old and doesn't freeze even in our MN winters), I don't have a good response. Just yesterday I looked over a system originally installed in 1999 that was dribbling from a section (Slant/Fin Sentry installed in 2022, which was now the 5th boiler in this system). Homeowner said he originally filled with 50/50 automotive that he "borrowed" from work, and each time they swapped the boiler, the installer just dumped more in along with some site water. Mind you, this antifreeze was stored in an open top drum next to the boiler and is now 26+ years old. I explained that this was likely a major contributing factor, but pulled a sample from a drain and found a 14% concentration with a PH of 4.2 in the system. Every drain and vent was corroded like crazy. I suggested that a new boiler would constitute a repipe since there was no P/S (CI boiler set to 140* running a radiant slab) and then do a thorough flush of the system and start fresh with new inhibited glycol, and the guy looked at me like I had 2 heads. Vehemently denied paying for antifreeze when he has some right here, then accused me of just being "another one of them salesmen". Okie dokie, sir. Please do enjoy replacing your boiler every couple years, I'll be going now!

You had better tell that to the millions of vehicles on the road every day with 20-30 year old coolant. Unless changing a water pump, thermostat, etc, 95% of people who do their own service never look at the coolant. I own a 1997 F250 that my father bought new and I bought from him in 2006, and the cooling system has never been touched; all coolant is factory original. Yes it's dumb and I should heed my own advice, but it's an experiment at this point. When a pinhole shows up in the water pump I'll let you know.

That's why I turn off the fill valve, then take the handle off and hide it.

If the system is filled with glycol mix, it needs to be topped up with glycol mix. If there's a leak you're better off finding it.

I've always heard you get sludge and plugged up heater cores. Honestly never heard of it eating through stuff though that would explain the sludge.

The automotive system is barely open. Some have a vented overflow tank but many now have a pressurizes tank that doesn't normally vent.

Even with a vented tank the entire system is supposed to be air free. If it's not that's when you get sludge from rusting etc. That was the big issue with Dexcool. Systems leaking, running low and then turning into a nightmare and people blaming the "new" antifreeze.

corrosion , sludge, low ph, all has to do with the amount of of oxygen that enters.

Tight steel, copper systems can maintain a good fluid regardless of water or glycol.

Ph is always a good indicator if fluid becoming aggressive

Makes me wonder if the hoses used in vehicles are O2 barrier

judging from what happens with the few radiant systems of the past that essentially use heater hose, i'm going to go with it is not oxygen barrier.

Many have pressurized tanks that are not open.

We're getting off topic, but vehicles typically have a radiator cap that opens at 12 PSI. When that happens, the coolant flows into a recovery tank. The radiator cap also opens when there is vacuum, when the engine cools coolant is sucked out of the recovery tank back into the system.

I've never seen a recovery tank that wasn't open to the atmosphere.

Even the GM style where the pressure cap is on the expansion tank are taking in and releasing atmospheric air to balance. The answer as to why they don't have O2 barriers is that they aren't sealed systems.

So does that mean a heating system with glycol doesn't need an o2 barrier?

as long as you check it and boost the oxygen scavengers as needed , then you don't need an O2 barrier.’

Open type outdoor wood boilers get a lot of oxygen and should have a scavenger program. I think they use strsight sulfites.

The hotter you run the system the higher the O2 ingress. So low temperature boilers on radiant are less probe to oxygen ingress.

Automotive glycols contain silicates, a compound containing silicone and oxygen, sodium silicate is one type. IAT inorganic Acid Technology. These coat the metal surfaces to prevent corrosion in the block and cooling system. OAT Organic Acid Technology is supposed to have a longer service life

But for some resson the silicates sludge up hydronic systems? So not to use automotive, even the PG type in hydronics.

Hydronic glycols use molybdate or phosphate blends for a film provider.

Although the silicates will also sludge up an automotive systems , which is why you test and replace it.

The OAT types