A heating system retrofitted to be operable through multiple heat stages at a constant fuel-air mixture 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.

A packaged heating and/or cooling unit for a production module for a heating, ventilation, air conditioning, and refrigeration (HVACR) system. The packaged unit includes a heat pump configured to provide heating and/or cooling; a connection to a piping distribution system to selectively connect to a hot fluid circuit and/or a cold fluid circuit; and a controller. The controller is configured to connect to and receive a signal from a building automation system for a heating requirement or a cooling requirement, and further configured to selectively control connection to either the hot fluid circuit or the cold fluid circuit and independently control the packaged heating and/or cooling unit based on the signal from the building automation system for either the heating requirement or the cooling requirement.

A modular heat pump water tank is provided. The modular heat pump water tank comprises a tank unit including a tank for containing heated water; a heat pump unit including a heat pump for providing heat to the tank; and a heat exchanger arranged externally to the tank for transferring heat from the heat pump to water from the tank. The tank unit and the heat pump unit are adapted for mounting to one another to form an integrated heat pump water tank.