The ThermixX ES96 takes advantage of a design feature found in older,
natural draft gas fired furnaces. The heat exchanger is made of heavy
metal, which retains heat for long periods of time after the burner is off.
The ThermixX harvest this retained heat by shutting off the gas while
the fan continues to circulate air around the heat exchanger, just as if
the burner was on. As the air is heated the heat exchanger cools, so
only a little free heat at a time can be taken before it becomes necessary
to ignite the burners again, during a normal heating cycle. When
utilizing the ThermixX, at least 20% less gas is burned which readily
translates into an immediate 20% saving on heating costs.