If you follow reputable project plans, you likely stand a chance at approval of your homemade waste oil furnace. The problem, as many commentators have noted, is that it is not only an unproven area of technology, but it is also technology that is still very much in its infancy. If you do want to use waste oil, it might be best to check on the Internet. There are several providers and systems listed as insurance-approved when starting out. A homemade system, as one author points out, assures the company carte blanche for disapproving just about everything.