I had a waste oil heater, in one of my shops, years ago. It was exactly that.., a waste. The thing needed to be cleaned, and taken apart, and rebuilt, like twice a week, on a good weeks. It was also, constantly, going airbound, and there was nothing that could be done about it. I had many of the company's tech's come out, to work on, and service it, and from the very first day, to the very last day, it was junk. I always ran "good" oil through it, and sometimes even new, or diesel, or other fuels. It was supposed to be able to burn anything with petroleum in it. (Except for anti-freeze, or things of that nature) I will never, go near one again.