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July 9, 2009
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Can I add antifreeze to my heating system?

Brad White replies:
Antifreeze is commonly done but like anything else, you have to do it the right way. Do not use automotive antifreeze (ethylene glycol, which also has silicates). Use only propylene glycol such as Noble No-Burst or Downtherm products with inhibitors.

Glycol is a sugar-alcohol type chemical. It is a potential food for bacteria and can turn acidic if your inhibitors run out by ongoing leaks and fresh water replenishment. You have to monitor your system water chemistry and pH.

Glycol will find leak points you never imagined, even if the system is now "tight." The lower internal surface tension of glycol tends to find these pathways. Valve stems, screw caps on hose-end valves, weak solder joints. . . you will see it in living color if there are any leaks.

Glycol will reduce the system capacity. If the system is generously sized or the structure insulated beyond the original system design, great, you are likely covered. If not, you may lose between 5- and 10-percent. Your circulator will work harder to deliver the fluid.

Glycol can be pumped in by hand or my machine pump. I like my Silver King Force Pump but an Axiom feeder is a great way to monitor leaks and avoid dilution. (Disconnect your make-up water when you use the Axiom).

Hot Rod replies:
That's it in a nutshell. There is more info up under the "resources" tab above. Look under Hot Tech Topics and search for "Glycol."