Induction stovetops (or hotplates) are a fantastic tool for chemists. They operate by passing current through a coil of copper wire which creates an oscillating magnetic field. This eliminates any source of ignition for your solvents (unless you exceed the auto-ignition point of naptha at 437°F). Though I still use a waterbath (I don't want naptha touching the cookware), I actually place the naptha directly in the pot while it's being heated (after extensive testing to ensure my theory was correct, I don't fancy losing any eyebrows).

Induction heating also offers more temperature control than the standard gas/electric stovetops.

If you don't have an induction stove (which I'd presume most do not), you can purchase a hotplate off amazon for ~$60.

That being said, a crockpot is also a viable alternative if you're on a tight budget. I purchased one a while back for $7 at a thrift shop.

Hot water works good, hot oil is often employed in chem as a more controllable heat source. Mind you, the more control you want the slow the heating process will be.

-Just depends on the situation at hand.