A water heater includes an inner water tube coil and an outer water tube coil separated by a drum baffle. The inner and outer coils extend above a top edge of the drum baffle by at least a full turn of each coil. A flue gas bypass path is defined between a top edge of the drum baffle and a top insulation layer above the inner and outer coils. Flue gases flow radially though the inner coil, up along the drum baffle, through the flue gas bypass path, and downwardly over the outer coil to heat water flowing through the inner and outer coils. The water flows into the outer coil at the bottom of the coil, winds upwardly through the outer coil in countercurrent flow with respect to the flue gases, then down through the inner coil.

An aspect of the present disclosure provides a flow channel cap plate that constitutes a combustion chamber assembly including a combustion chamber and a plurality of insulating pipelines disposed on left/right side surfaces of the combustion chamber, the flow channel cap plate forming an insulating flow channel by covering the front surface of the combustion chamber, the flow channel cap plate including an inlet part including an inlet, and an inlet flow channel cap covering the front surface of the combustion chamber, an inlet space part is formed by covering the front surface of the combustion chamber with the inlet flow channel cap, the inlet is an entrance of the insulating flow channel, the plurality of insulating pipelines include a plurality of inlet insulating pipelines, and the inlet space part is a space that communicates the inlet with the plurality of inlet insulating pipelines.

A secondary heat exchanger includes a case and a first heat transfer tube portion. The case includes a box body and a first closing member. The box body is provided with a second opening on one side in a third direction. A first assembly in which the first heat transfer tube portion and the first closing member are assembled integrally is mounted to the box body so that a plurality of first heat transfer tubes are is inserted into the box body from the second opening and so that the second opening is closed by the first closing member.

Aspects of the invention provide a heat exchanger that includes a shell coupled to a top tube sheet and a bottom tube sheet. The shell at least partially defines an interior region. The heat exchanger also includes a burner positioned to deliver combustion gases into the interior region. A plurality of tubes, configured to circulate a fluid therein, extend through the interior region around the burner. The heat exchanger further includes a divider that extends within the interior region from the top tube sheet to the bottom tube sheet and between one of the plurality of tubes and another non-adjacent tube of the plurality of tubes. The divider and the plurality of tubes define a receiving section of the interior region for receiving combustion gases from the burner and an exhaust section of the interior region in fluid communication with a combustion gas vent.

Aspects of the invention provide a heat exchanger that includes a shell coupled to a top tube sheet and a bottom tube sheet. The shell at least partially defines an interior region. The heat exchanger also includes a burner positioned to deliver combustion gases into the interior region. A plurality of tubes, configured to circulate a fluid therein, extend through the interior region around the burner. The heat exchanger further includes a divider that extends within the interior region from the top tube sheet to the bottom tube sheet and between one of the plurality of tubes and another non-adjacent tube of the plurality of tubes. The divider and the plurality of tubes define a receiving section of the interior region for receiving combustion gases from the burner and an exhaust section of the interior region in fluid communication with a combustion gas vent.

A heat exchanger unit according to the present invention includes a sensible heat exchanger including a sensible heat exchange pipe disposed in a sensible heat exchange area for heating water used for heating by receiving sensible heat generated by a combustion reaction, wherein the sensible heat exchange pipe receives the water used for heating and flows same through the interior, and a sensible heat fin disposed in the sensible heat exchange area. The sensible heat fin is formed in a plate shape across the sensible heat exchange pipe and penetrated by the sensible heat exchange pipe; and a latent heat exchanger positioned downstream from the sensible heat exchange area on the basis of a reference direction, which is a flow direction of combustion gas generated during the combustion reaction, the latent heat exchanger including a latent heat exchange pipe disposed in a latent heat exchange area.

A heat exchanger includes a case, fins, and heat transfer tubes. Combustion exhaust gas passes downward in the case. The fins are disposed at a lower portion of the case and arranged in the first direction. Each of the fins includes a first end and a second end that is an opposite end from the first end in a second direction intersecting the first direction. Each of the fins includes through holes in which the heat transfer tubes are inserted. Each of the fins includes heat receiving portions arranged in the second direction and connecting portion connecting the heat receiving portions. The heat receiving portions include a first heat receiving portion disposed at the first end. The first heat receiving portion includes a first recessed portion recessed from an outer edge of an upper part of the first heat receiving portion.

A premixed low-nitrogen gas boiler is provided, which includes a reversed flow-swirl mixer being opposite mixing of natural gas and air. A flow deflector is arranged at a gas mixture outlet of the reversed flow-swirl mixer. An upper flow equalizing plate and a lower flow equalizing plate are arranged below the flow deflector, the upper flow equalizing plate is positioned above the lower flow equalizing plate, and a channel for enhancing mixing of gas mixture is formed between the upper flow equalizing plate and the lower flow equalizing plate. A comb-shaped water-cooled burner is arranged at the rear end of the lower flow equalizing plate, a combustion chamber is arranged at the rear end of the comb-shaped water-cooled burner, hearth tube bundles are arranged in a ladder-shaped convergent hearth, and the hearth tube bundles form an inner loop with a working medium water-steam mixture in a hearth water tank.

A premixed low-nitrogen gas boiler is provided, which includes a reversed flow-swirl mixer being opposite mixing of natural gas and air. A flow deflector is arranged at a gas mixture outlet of the reversed flow-swirl mixer. An upper flow equalizing plate and a lower flow equalizing plate are arranged below the flow deflector, the upper flow equalizing plate is positioned above the lower flow equalizing plate, and a channel for enhancing mixing of gas mixture is formed between the upper flow equalizing plate and the lower flow equalizing plate. A comb-shaped water-cooled burner is arranged at the rear end of the lower flow equalizing plate, a combustion chamber is arranged at the rear end of the comb-shaped water-cooled burner, hearth tube bundles are arranged in a ladder-shaped convergent hearth, and the hearth tube bundles form an inner loop with a working medium water-steam mixture in a hearth water tank.

A heat exchanger unit according to the present invention comprises: a sensible heat exchanger including a sensible heat exchange pipe disposed in a sensible heat exchange area for heating water used for heating by receiving sensible heat generated by a combustion reaction, wherein the sensible heat exchange pipe receives the water used for heating and flows same through the interior, and a sensible heat fin disposed in the sensible heat exchange area, wherein the sensible heat fin is formed in a plate shape across the sensible heat exchange pipe and penetrated by the sensible heat exchange pipe; and a latent heat exchanger positioned downstream from the sensible heat exchange area on the basis of a reference direction, which is a flow direction of combustion gas generated during the combustion reaction, the latent heat exchanger including a latent heat exchange pipe disposed in a latent heat exchange area.