My harman p35i has saved me thousands in oil bills since I installed it in January 2012. But I still burn oil to heat my water. I just bought 200 gallons ($820) which is what I spend a year on oil. Now my 35-plus-old oil burner is giving out and my chimney needs work. I did some research, called my local utility, got five bids from contractors, engineered an interest-free loan and equipment rebates, and am set to get gas heat in my house this spring. But I have all that oil. So I'm using it. I love the Harman and hate oil heat but have to admit I like to hear the radiators pinging again and heating every corner or my house, as opposed to my pellet stove just space heating my living room while fans push air around the house. Next winter when I have gas, how much will I use the Harman? It remains to be seen, but for now it's like pre oil-embargo America in my house -- I'm cranking the oil heat and listening to bad early 70s music.