Minimize "excess air" in boiler operations. In order to ensure complete combustion, most boilers are designed to operate with excess air (more air than is theoretically required for the combustion process). However, this excess air reduces the boiler's efficiency. If excess air can be minimized, efficiency gains of 1 to 2 percent can be realized. Excess air controllers (sometimes called "O2 trimmers") are available. They control excess air by sampling combustion products and adjusting the amount of air supplied to the burner accordingly. For a 250 hp boiler running 2,000 hours per year, the installation of an O2 trim system would result in an increase in efficiency of 1 to 2 percent, which is equivalent to an energy cost savings of about $1,700. Initial cost of a unit for a package boiler of this size is approximately $9,000. If the boiler ran for more than 2,000 hours per year, the savings would be correspondingly higher.