Last month I fired up my kerosene heater for the first time in seven years. It still had a small amount of kerosene in it and I wanted to use the old stuff up and condition the wic. I know , I know you should empty the tank at the end of the season according to the owners manual. I've got my mind right now and will take better care of my life saving heat source. My point is after seven years the kerosene burnt great, no smoking just like new stuff. I had always wandered how long kerosene would last and if you needed to add a fuel conditioner to it. Now I feel confident that I can store it and it wont go to bad. I also have a heat Buddy and 3 20# tanks with a 12 foot hose.