PRODUCTS STEAM BOILERS | HHO Generators (yullbrownsgas.com) In a conventional boiler, fossil fuel is burned by reaction with the oxygen and hydrogen gases in the surrounding air. The hot combustion gases produced pass through a heat exchanger in which the surfaces transmit the heat from the combustion products to the water, thus raising the water’s temperature. One of the hot gases produced in the combustion process is water vapor (steam) which arises from burning the hydrogen content of the fossil fuel as hydrogen reforms to water after combustion. Other hot gases produced are classified as emissions basically comprised of unburnt fossil fuel and particles from the fossil fuel’s combustion and are deadly poisonous.