There are at least two ways to describe a furnace’s thermal performance. The percent-available heat indicates thermal efficiency, while the adiabatic flame temperature indicates heat-transfer intensity. Both factors can be used to indicate a furnace’s productivity.
the efficiency of a heating process depends on knowing (or calculating) the
heat of combustion of a fuel. In some cases, it’s sufficient to
use an approximate value, such as 1,000 BTU/ft3
for natural gas.
Efficient process heating
requires recovery of the largest possible fraction of a fuel’s combustion heat
into the material being processed. There are many avenues of loss in the
operation of a heating process. Typically, the dominant loss is energy leaving
with the offgas.