What all has to be modifed to burn waste oils?
Now that you have a basic idea of how a furnace works, do a search for "waste oil burner" on YouTube and you will see burner conversions that various people have done - nice, but no real info on how to do it. I hope to be able to explain and show you how I did it which I think is the best method.
First of all, the burner will undergo modification and then what I call a preheat/constant fuel level tank will be created and attached to the side of the furnace. Before I get into the modification I will first explain why the modifications are necessary. Heating oil (#2 diesel) has a viscosity that is much lower than that of other waste oils such as waste motor oil (WMO), waste transmission fluid (WTF), or waste vegetable oil (WVO). Because an unmodified burner pumps heating oil to a very tiny nozzle hole under high pressure, these waste oils would immediately clog up with no modification. Well, we could heat the oil hot enough to get the viscosity down close to diesel, but carbon deposits and stuff in the various waste oils would still easily clog them unless they are very finely filtered. One of the objects of this design is to not have to finely filter the waste oils which could incur a lot of time and expense. Therefore another approach is taken - use a different type of nozzle that can burn oils that can be filtered with a simple cleanable mesh filter. I am currently using a 50 mesh cleanable stainless steel filter to filter my waste oils, but this will vary depending on the nozzle used - more about nozzles later.