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Heating Surface
(Steam Boilers) the aggregate surface exposed to fire or to the heated products of combustion, esp.
of all the plates or sheets that are exposed to water on their opposite surfaces; -
called also fire surface.
Fire Surface
the surfaces of a steam boiler which are exposed to the direct heat of the fuel and the products of
combustion; heating surface.
Heating value (or calorific value) is used to define the amount of heat released during the
combustion of a fuel or food. It is measured in units of energy per amount of material. Depending
on the context, heating values may be reported as Btu/m³, kcal/kg, kJ/kg, J/mol, or a variety of other
combinations of units. Heating value in commonly determined by use of a bomb calorimeter.
The quantity known as higher heating value (or gross calorific value or gross energy) is determined
by bringing all the products of combustion back to the original pre-combustion temperature. The
quantity known as lower heating value (or net calorific value) is determined by subtracting the heat
of vaporization of the water in the by-product from the higher heating value results. The lower
heating value is what is typically used for vehicle engine analysis.
Since most gas burning appliances cannot utilize the heat content of the water vapor, gross calorific
value is of little interest. Fuel should be compared based on the net calorific value. This is
especially true for natural gas, since increased hydrogen content results in high water formation
during combustion.