The energy loss in a combustion chamber, as a result of pressure drop, is generally found to be of relatively greater importance than the losses from combustion inefficiency. Therefore it must be included in any parameter which claims to state the efficiency of the burner. Combustion efficiency alone does not serve this purpose. A method of comparison is suggested and developed which allows combustion chambers to be compared on an over-all basis. By this method, any combustion chamber is assigned a single energy efficiency for each inlet condition, which includes the effects of both combustion efficiency and pressure drop.