Yes pretty common, around here, to use it. Used a lot in seasonal homes that
get shut down the middle of winter, but also for those that have a problem
with a seldom used zone freezing.
There is a special, non toxic, antifreeze you are supposed to use if you are
connected to a municipal water supply. I know some that use dexcool.


If you're going to be adulterating your hydronic-system water with
anything that didn't come out of the municiple water-supply,
then there should be an air-gap between the two.