Some of the commenters suspected issues like flame rollout and corroded heat exchangers — problems ... can slash your electricity use for heating by up to 75%. That's not all.

When a fuel is burned in oxygen and water is one of the combustion products, the adiabatic flame ... heat exchanger) is still higher than the boiling point of water and the heat of transformation of ...

A furnace heat exchanger keeps dangerous gases out of the air circulating in the building. It's a must-have on any furnace that burns gas or oil.