i worked in a workshop that used to have a old heater in the corner it used to run on all the old sump
oil we got from
oil changes free heating i think it would run on kero and diesel as well. it was quite a large workshop and it used to warm it up really well .
once it was up and going there was never any smoke coming out of the flue the boss would fill it last thing and let it run all night if we had done enough
oil changes during the day lol .
not sure if the epa would allow them nowdays tho