Why does the heat smell when the steam or furnace systems are turned on? What is that smell? Sometimes customers tell me they can tell the heat is on because they can smell the steam. Or forced air people definitly know when the heat first gets turned on. What is that about? Well it isn't the heat your smelling! Its the ammonia that is being released as dust roasts on your heating surface, be it a radiator, convector, or forced air heat exchanger. The link is an article on this subject from a 1912 heating and ventilating magazine. Very interesting. It kind of makes radiant heat look even better. Break out you dust brushes!