How do you clean a propane gas fireplace and an oil burning furnace?

First of all you need to know what you are doing when you start to clean these type of items. Usually the oil burner will need a new nozzle,electrode re-gap,pump pressure test to start with.

Same type of stuff for the fireplace except it will be gas components you will be working on.

Now if you just want to clean the outside get a duster but leave the other stuff to a professional with years of experience doing this type of work.