A heating, ventilating, and air conditioning (HVAC) system includes a furnace having a primary heat exchanger and a secondary heat exchanger, where the primary heat exchanger and the secondary heat exchanger form a heat exchange relationship between an airflow and an exhaust gas, and where the primary heat exchanger is positioned upstream of the secondary heat exchanger, a burner configured to generate the exhaust gas, a sensor configured to monitor an ambient temperature, and a control system configured to receive feedback from the sensor, compare the feedback to a threshold, operate the furnace in a first mode when the ambient temperature exceeds the threshold, and operate the furnace in a second mode when the ambient temperature is at or below the threshold, where the furnace operates above a condensation temperature when in the second mode, such that the exhaust gas does not condense when operating in the second mode.

The present disclosure is directed to a tankless water heater and systems and methods of using the same. The tankless water heater embodiments of the present disclosure can be configured to have a plurality of independently operable heat exchangers that can be used individually or collectively, in any combination, to heat water based on the level of demand for hot water. Embodiments can be configured for randomly selecting which heat exchangers are used to heat the incoming water. Embodiments of the present disclosure can also be configured to flow water through heat exchangers that are not being used to heat water and direct such water to a recirculation loop.

A combustion apparatus includes a burner configured to produce flames, a first flame rod and a second flame rod, and a controller. The burner is configured to be controlled, by the controller, to be in a first output state, and a second output state in which output is smaller than in the first output state. The first flame rod makes contact with the flames produced at the burner in a normal combustion state. The second flame rod makes contact with the flames produced at the burner in the normal combustion state when the burner is being controlled to be in the first output state, and does not make contact with the flames produced at the burner in the normal combustion state when the burner is being controlled to be in the second output state.

A heat exchanging unit exchanges heat between a fluid to be heated and exhaust gas. The heat exchanging unit includes a heat exchange portion, a header portion, and a flow changing portion. The heat exchange portion includes a heat exchange pipe in the interior of which the fluid to be heated flows. The header portion is connected to the heat exchange pipe, the header portion allowing the fluid to be heated to flow from the header portion to the heat exchange pipe or from the heat exchange pipe to the header portion. The flow changing portion changes the state of flow of the exhaust gas introduced into the heat exchange portion.

An exhaust duct includes an upper duct being open at opposite ends thereof and a lower duct being open at a tip end thereof. One end of the upper duct is connected, inside an enclosure of a water-heating device, to an exhaust adaptor disposed on the enclosure, and an opposite end of the upper duct communicates with the tip end of the lower duct. The upper duct is connected to the lower duct so as to be slidable along a reference direction in which the lower duct extends from the tip end of the lower duct, and the upper duct is configured to be separated from the exhaust adaptor by sliding along the reference direction.

A heating, ventilating, and air conditioning (HVAC) system includes a furnace having a primary heat exchanger and a secondary heat exchanger, where the primary heat exchanger and the secondary heat exchanger form a heat exchange relationship between an airflow and an exhaust gas, and where the primary heat exchanger is positioned upstream of the secondary heat exchanger, a burner configured to generate the exhaust gas, a sensor configured to monitor an ambient temperature, and a control system configured to receive feedback from the sensor, compare the feedback to a threshold, operate the furnace in a first mode when the ambient temperature exceeds the threshold, and operate the furnace in a second mode when the ambient temperature is at or below the threshold, where the furnace operates above a condensation temperature when in the second mode, such that the exhaust gas does not condense when operating in the second mode.

A heat exchanger includes a lamellar structure of a plurality of parallel heat exchange elements with an intermediate air gap between each pair of adjacent heat exchange elements. Along a longitudinal direction of the lamellar structure the heat exchange elements is interconnected in a top portion of the lamellar structure that forms an inlet channel through the heat exchange elements and in a bottom portion of the lamellar structure that forms an outlet channel through the heat exchange elements. The heat exchange elements form parallel channels between the inlet and the outlet channels. In the outlet channel, the heat exchanger includes a filler body, that is filling up a lower level of the outlet channel and forms a floor along the longitudinal direction of the lamellar structure.

A water heater includes a heat exchanger, a heat pump, a first valve in fluid communication with the heat exchanger and the heat pump, and a controller configured to control the first valve. The first valve can be configured to direct water flow toward at least one of the gas heater or the electric heat pump. A second valve in fluid communication with the first valve and the heat pump can be provided, and the controller can be further configured to control the second valve. A water heater inlet and a water heater outlet can be included and in fluid communication with the first valve, and the controller can be configured to monitor a temperature of water entering the water heater inlet and control the first valve dependent upon the monitored temperature.

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.

A heater including a housing, a first tankless heater, a second tankless heater, a first and second flow directing elements, the first flow directing element in communication with the first tankless heater and the second flow directing element and the second flow directing element in communication with the second tankless heater, and a controller in communication with the first and second tankless heaters and the first and second flow directing elements, the controller configured to control the first and second flow directing elements to control flow to one or both of the first and second tankless heaters.