Patent ID: 6863523

Claim:
A system comprising: (a) a boiler configured to receive combustion air and to generate flue gas as a byproduct of burning fuel mixed with the combustion air; (b) combustion air conduit configured to direct the flow of the combustion air to the boiler; (c) flue gas conduit configured to direct the flow of the flue gas away from the boiler; (d) a first fan coupled to the boiler and configured to force combustion air through the combustion air conduit to the boiler; (e) a first air heater coupled to the first fan and to the boiler via the combustion air conduit and positioned along the combustion air conduit between the first fan and the boiler; and (f) a second air heater coupled to the boiler via the flue gas conduit, wherein the flue gas conduit is configured to direct more flue gas to the second air heater than to the first air heater.