Over here in the Spud-highlands it gets farking cold at 6k ft & I heat the shop with free jet-A & used oil in a home built burner. The jet-a is sump fuel from Pocatello airport that can't be recycled back into the fuel farm. Waste oil companies charge to take this away, I do it for nothing that saves them money & get about 300 gallons over a 12 month period. I also get about 150 gallons of 100LL that I run in the plow truck, the front end loader & the jet boat, also free.
A lot of the locals bring me their used oil plus I have a supply of hydraulic oil from an elevator company.
Having the Caribou National Forrest at my back door I used to burn wood in a double stack barrel burner & drip used oil onto that. Then I converted over to just oil by putting a small 4" stainless bowl in the bottom to keep the heat that sits right under a 1-1/2" pipe connected to a blower. My jet-a comes down a 1/4" stainless tube inside that & I regulate it with a T valve. The waste oil comes down the 1-1/2 pipe with the air from a separate tank with a 1/2" gate valve. I start it on jet-a to get the bowl red hot then turn on the waste oil & I can run either or both fuels & turn the heat up or down with the valves. Some of the used oil is dirty & builds up a carbon crust in the bowl that needs to be cleaned out but that's easy enough. It costs me less than $20 / month to run the blower 24-7, that's some cheap heat right there people! By the way, I live in the shop with the Streamliner.
A quick lube place said they would give me 500 gallons of used ATF but I never took them up on it, I have enough now.
Sid.