Furnace Efficiency

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Carry out an energy balance calculation around the furnace, and all will become clear.

It depends on what kind of furnace you are talking about, and there are lots of them.

It also depends on the fuel you are using and again, there a lots of them.

Some basic things are:

-amount of excess air

-wall losses

-flue gas temperature

These are but a few of the many factors that influence a heat balance on a furnace.