Why refine tar sands oil?
Tar sand oil is extremely heavy and would produce a lot of soot. It also contains a lot of sulfur, so the smoke would contain a lot of sulfur dioxide. This means, that burning it would require exhaust purifications. This in turn would require costly equipment that is not practical for individual household. 

Furthermore, heavier fractions of oils have hard time burning. They have to be heated significantly before a flame can form.

Consequently, tar oils must be refined to be of practical use. This includes three key processes:


hydrocracking, which breaks down larger molecules into smaller ones, that produce less soot and burn easier.
hydrothreatment, to remove sulfur, metals (yes, heavier oil fractions contain measurable amount of metals, vanadium and nickel in particular, that are known cancerogenes)
distillation, separating lighter fractions from the heavier ones. Typically fractions C5-C20 are used for internal combustion engines, some С21+ are usable in industrial-grade furnaces, and the heaviest and most troublesome fractions are used as asphalt.


So, propane or propane-butane mixture is a lot more practical for small furnaces. It is very easy to refine, produce no smoke and contains no sulfur, so burning it is pretty easy. Furthermore, in can be liquefied under pressure, but it is still a gas at most common conditions. So equipment to burn it is extremely simple and exhausts are virtually harmless in most cases. Propane is reasonably cheap in most setups to use.