GAS WATER HEATER
You may be smelling the burnt propane smell. To ease your mind you can use a soapy solution and put it on any gas line connections to check for leaks (bubbles). Look into the burner box of heater, what color is the flame just off the burner to almost the end of the flame? If ornage you are not getting enough cumbustion air and could have a cobweb in the venturi tube of burner. This may acount for the smell, if enough incomplete burning of propane is present.