I have a friend who wants to buy a 3000 sq.ft. 100 year old home with hot water heat. She has been told to replace the old boiler sys. with a forced air unit. and she will save a lot in in heating costs. I am not so sure if that is true. Can any body tell me whats the most efficient way to heat an old 3 story home? A comeplete conversion or just upgrade the boiler and radiators? The boiler and radiators are leaking and need to be replaced soon.