Is it safe to put an empty propane tank in your attic across from the furnace?

Question

ask for more details if needed

Answer 1

Define empty.

An empty tank usually still has a small amount of propane in it, which is still highly flammable.

Do it only if you want a new home.

Answer 2

Even an "empty" tank could still be filled with flammable vapors. Probably your local fire code prohibits you from even storing that in your house.