In case anyone interested.....I have Charmaster wood furnace, 30 yo, and been working ok. It has a water heat coil in it that I just figured out how to replace, since the manufacturer is now out of business. I had local guy make one out of stainless, if anyone is interested. Old ones were galvanized 1" pipe that would last about 10 years. My natural gas bill during winter is 5-10 dollars a month for gas charge part of bill. fred hogan, hamilton ohio