An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120V operation, the large diameter 9-ohm coil is used alone to provide the lowest possible watt density. For 240V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120V operation, the large diameter 9-ohm coil is used alone to provide the lowest possible watt density. For 240V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120 V operation, the large diameter 9 ohm coil is used alone to provide the lowest possible watt density. For 240 V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120 V operation, the large diameter 9 ohm coil is used alone to provide the lowest possible watt density. For 240 V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

Embodiments described herein generally relate to a domestic hot water (DHW) preheater operable to supply domestic hot water to a structure and/or to preheat a cold return of a space heating system.

An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120V operation, the large diameter 9-ohm coil is used alone to provide the lowest possible watt density. For 240V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

An improved boiler apparatus having multiple resistive heating elements are provided with fixed resistances that can be rewired to allow dual voltage capability and at the same time, reduced watt density. For 120V operation, the large diameter 9-ohm coil is used alone to provide the lowest possible watt density. For 240V operation, all three heating coils are wired in series, creating a low watt density but high wattage heater.

An improved boiler apparatus having a removably couplable heating element that can have resistive heating elements are provided with fixed resistances that can be rewired to allow variable wattage usage of the heating element. Some heating element assemblies can include more than one heating coils or heating element. The heating elements can be wired in series, or parallel thereby creating a low watt density but high wattage heater.

An improved boiler apparatus having a removably couplable heating element that can have resistive heating elements are provided with fixed resistances that can be rewired to allow variable wattage usage of the heating element. Some heating element assemblies can include more than one heating coils or heating element. The heating elements can be wired in series, or parallel thereby creating a low watt density but high wattage heater.

The present application provides a temperature control device for fluids, which comprises a furnace, a fluid pipe, a plurality of regenerative members, a burner, and an air control device. The burner heats the furnace to store heat to the regenerative members inside the furnace and conduct the thermal energy to the fluid pipe. The fluid pipi outputs a heated liquid. In addition, the regenerative members further produce and transport heated air to the air control device. The air control device converts the heated air to output cooled air.