A high turndown furnace for an air handling system. In one example, the furnace includes a plurality of tubes divisible by four with a first modulating valve supplying gas to of the tubes and a second modulating valve supplying gas to of the tubes. In one aspect, the furnace is capable of providing a 16:1 turndown. In one aspect, the furnace is capable of providing seamless turndown operation throughout the entire firing range.

A heating control device including input/output ports, a memory operable to store smoke output thresholds, and a microprocessor. The microprocessor is configured to transmit a first electrical signal to operate an air circulation fan at a first speed and a heating unit in a first configuration to burn a lubricant at a first temperature where less than all of the burners are active. The microprocessor is further configured to obtain a smoke output measurement for the first temperature, compare the smoke output measurement to the smoke output threshold, and transmit a second electrical signal to transition the air circulation fan to a second speed to burn the lubricant at a second temperature that is greater than the first temperature when the smoke output measurement is less than the smoke output threshold and is less than the first temperature when the smoke output measurement is greater than the smoke output threshold.

A high turndown furnace for an air handling system. In one example, the furnace includes a plurality of tubes divisible by four with a first modulating valve supplying gas to of the tubes and a second modulating valve supplying gas to of the tubes. In one aspect, the furnace is capable of providing a 16:1 turndown. In one aspect, the furnace is capable of providing seamless turndown operation throughout the entire firing range.

A heating control system including an air circulation fan, a heating unit, a memory, and a microprocessor. The microprocessor is configured to operate the air circulation fan at a first speed and the heating unit in a first configuration where less than all of the burners are active. The microprocessor is further configured to determine a first temperature difference, compare the first temperature difference to a first temperature difference threshold, and transition the air circulation fan from the first speed to a second speed when the first temperature difference is less than the first temperature difference threshold. The microprocessor is further configured to determine a second temperature difference, compare the second temperature difference to a second temperature difference threshold, and transition the air circulation fan from the second speed to a third speed when the second temperature difference is less than the second temperature difference threshold.

A controller is configured to set total stop in which operations of all of a plurality of water heaters are stopped when an abnormal condition of a fan or an abnormal condition in communication is sensed in any of the plurality of water heaters while at least one of the plurality of water heaters is operating. The controller is further configured not to set total stop when an abnormal condition of the fan or an abnormal condition in communication is sensed in at least one of the plurality of water heaters while a sensing element for sensing a backflow of an exhaust from an exhaust path assembly is connected to the controller.

A modulating heating system includes a tube heat exchanger having a plurality of burners, a combustion air blower (CAB) having an exhaust vent connected with the plurality of burners, the CAB operable at a first speed and a second speed, a first valve connecting a fuel source to a first subset of the plurality of burners, and a second valve connecting a fuel source to a second subset of the plurality of burners, wherein the first and second valves each have a low fire rate and a high fire rate. The heat exchanger is operable through multiple heat stages at a constant fuel-air mixture.

A water heater includes a plurality of stages of burners, a water supply pipe, a hot water outlet pipe, a heat exchanger, a passing water quantity control unit, a temperature detection unit, and an operation control unit. The operation control unit, upon confirmation that a predetermined start condition of a passing water restriction is satisfied at a start of a hot water supply, performs the output hot water temperature control by calculating a target flow rate that causes no switching or a minimum count of switching of the combustion stages of the burners and configuring the passing water quantity control unit to have the target flow rate. The operation control unit, upon confirmation that a predetermined release condition of the passing water restriction is satisfied, executes the passing water control in which the passing water quantity is returned to the predetermined water quantity by gradually releasing the passing water restriction.

A water heater includes a burner, a heat exchanger, a passing water quantity control unit, a temperature detection unit, and an operation control unit. The operation control unit performs the output hot water temperature control by configuring the passing water quantity control unit to have a predetermined passing water quantity that is further restricted compared with a predetermined water quantity, and upon confirmation that a predetermined release condition of the passing water restriction is satisfied, executes the passing water control in which the passing water quantity is returned back to the predetermined water quantity by gradually releasing the passing water restriction, and the operation control unit, when a predetermined undershoot factor of the detected temperature is confirmed while the passing water quantity is returned back to the predetermined water quantity, temporarily stops the release of the restriction of the passing water quantity until the undershoot factor is resolved.

The invention relates to the technical field of a water heating device, and particularly discloses a control method of a gas water heating device and a gas water heating device. The gas water heating device comprises a burning device which includes at least two groups of burners; the control method of the gas water heating device comprises: determining whether the currently required load is within a common load range obtained in advance or not in the case that a first preset condition is met; if it is so, controlling a burner or burner combination corresponding to a common segment to conduct burning; the power range corresponding to the common segment comprises the common load range. With the present scheme, the constant-temperature effect of the water heater can be improved, and user experience is improved.

The invention relates to the technical field of a water heating device, and particularly discloses a control method of a gas water heating device and a gas water heating device. The gas water heating device comprises a burning device which includes at least two groups of burners; the control method of the gas water heating device comprises: determining whether the currently required load is within a common load range obtained in advance or not in the case that a first preset condition is met; if it is so, controlling a burner or burner combination corresponding to a common segment to conduct burning; the power range corresponding to the common segment comprises the common load range. With the present scheme, the constant-temperature effect of the water heater can be improved, and user experience is improved.