Abstract: A heat exchanger includes a burner configured to burn a combustible gas to produce heat, a heat exchanger configured to receive the heat from the burner, a flow sensor configured to measure a flow rate of a coolant passing through the heat exchanger; and a controller comprising processing circuitry. The processing circuitry receives flow data from the flow sensor and controls a firing rate of the burner based on a predetermined relationship between a differential temperature of coolant flowing through the heat exchanger and the coolant's flow rate.

Abstract: A dual fuel boiler has fuel delivery apparatus coupled to its burner section through a pressure regulator and operative to deliver to the burner section, from sources thereof, a selectively variable one of (1) a first fuel at a pressure greater than the pressure regulation setting of the pressure regulator, and (2) a second fuel at a pressure less than the pressure regulation setting, the second fuel having a Wobbe index greater that that of the first fuel. The first fuel is flowed to the burner section via a branch supply line in which first and second electromechanical two position, two-way, two position valves are installed in series in opposite normal flow orientations to thereby prevent backflow of the second fuel into the source of the first fuel.