Correct me if Im wrong,but your heating system is freezing up while its operating? IMHO I would correct the issue of why your system is freezing. Lack of circulation? Lack of insulation? Pipes running inside an outside wall again without proper insulation?
Im no expert but antifreeze in the system sounds like a bandage over a larger issue.I have (and so have many others) never had a freezing issue with my hot water heat. Temps to -30deg F and 30mph winds never frozen heat pipes.That includes the 2nd level of the house that I keep cold since the kids have moved out.