The majority of the people who usually invest in waste oil heaters of any kind have their own supply of used motor oil.
A lot of my customers have been business owners of oil change businesses. Other clients of mine have some sort of automotive mechanic or tire shop but oil changes is one of many services they offer.
Other people who want to invest in waste oil furnaces or boilers have large commercial fleets of some sort. Some have a fleet of large diesel trucks. One of my newest customers is a railroad company. With both these types of fleets one oil change on a vehicle, or train, can yield at least 8 gallons of used motor oil.
For these businesses getting a decent supply of oil is not a problem at all.
In fact, costs them more money at times not to have a waste oil heater because they were having to spend money disposing of it.
If you do not own a business that has access to its own supply of used motor oil please do not discount buying one of these machines. There are many business owners who have been able to fully utilize used waste oil heating technology without having an actual supply of their own.
Will it be a little harder- yes.
Will you have to be a little more creative- yes.
Is it impossible- absolutely not!
Why do I say that? Look around you. Every motor ever made needs oil to lubricate it. And if that oil is not changed, at least periodically, that motor will not last long. Millions of oil changes are being preformed every single day.
That waste oil is going somewhere. You just have to find a way to get it.
It may be necessary to call around. Every mechanic shop will have several barrels laying around. Many of them will be more than happy to give it to you. You will just need to pick it up and come up with a good system to filter it.
There is an endless pool to get waste oil from. I know many people who have been able to do it. I can give you some ideas.
A friend of mine wrote an excellent article on searching for used waste motor oil for your waste oil heater. If you do not have you own supply I would suggest you read it. There may be angles you have not thought about yet.