Why does my furnace smell like rotten eggs?
Natural gas does not have a natural odor, so utility companies add a compound to give a smell. This allows homeowners to detect a gas leak more easily. If your house has the smell of rotten eggs (or sulfur), this is a sign of natural gas leak. If you know how to, shut off your gas supply line and then immediately call your gas company while evacuating your home.
With propane furnaces, smelling rotten eggs usually signals that you’re low on fuel.