The question of using automotive type antifreeze in hydronic heating applications seems to come up over and over. Steffes does not recommend the use of these materials. We have done some research on this issue and feel that it may or may not be effective. Some authorities in the industry feel that the different corrosion inhibitors in automotive antifreeze could separate out and cause blockages and/or other problems as well as even damage the hydronic heating system. Many of the automotive types of antifreeze are toxic; therefore, extremely unsafe in the event of a system leak. When looking at the possible savings, it seems that it simply does not pencil out when you factor in the potential costs of problems, safety, and field liability.