I'm going to be using a boiler for the first time this season, and I really want to avoid buying ~$1200 in antifreeze ... so I was wondering: If I'm away from home, and I allow the boiler to go out but leave the circulation pump running, will the water-to-air heat exchanger in my plenum rob enough heat from my propane furnace to keep the boiler from freezing as long as I leave the house at a reasonable temperature?