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.

A water heating system can include a first tank-based water heater having a first inlet line and a first outlet line, where the first inlet line provides unheated water to the first tank, and where the first outlet line draws heated water from the first tank. The system can also include a first tankless water heater having a second outlet line, where the second outlet line of the first tankless water heater provides the heated water to a first heated water demand. The system can also include a first valve that controls an amount of the unheated water flowing through the first inlet line to the first tank-based water heater. The system can further include a controller operatively coupled to the first valve, where the controller controls a position of the first valve based on the first heated water demand and a first capacity of the first tankless water heater.

A water heating system can include a first tank-based water heater having a first inlet line and a first outlet line, where the first inlet line provides unheated water to the first tank, and where the first outlet line draws heated water from the first tank. The system can also include a first tankless water heater having a second outlet line, where the second outlet line of the first tankless water heater provides the heated water to a first heated water demand. The system can also include a first valve that controls an amount of the unheated water flowing through the first inlet line to the first tank-based water heater. The system can further include a controller operatively coupled to the first valve, where the controller controls a position of the first valve based on the first heated water demand and a first capacity of the first tankless water heater.

The present invention provides an electric boiler having a heating element surrounded by a thermally conductive inner container to define an inner passage about the heating element, the inner container having an inlet 13, 14 and an outlet for a flow of water and is arranged such as to cause water received at the inner container inlet to flow along the inner passage in close proximity to a surface of the heating element, the boiler further comprising an outer container in which the inner container is substantially located, the outer container defining an outer passage about at least part of the inner container, the outer container having an outlet into the inner container wherein the outer container is arranged such as to cause water to flow along the outer passage in close proximity to a surface of the inner container, such that water received in the boiler makes at least a double pass through the boiler to increase the potential heat transfer to the water.

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.

A waste heat recovery device with a first heat medium side inlet; a first heat medium side outlet; a first heat medium flow path; a second heat medium side inlet; a second heat medium side outlet; a second heat medium flow path; a heat exchanger that exchanges heat between the first heat medium and second heat medium; an expansion tank in the first heat medium flow path; a bypass flow path that causes the first heat medium to flow and bypass the heat exchanger; and a mixer where the bypass flow path and first heat medium flow path merge together. The mixer is configured to adjust a ratio of a flow rate of the first heat medium in the bypass flow path and a flow rate of the first heat medium in the heat exchanger, such that the temperature of the first heat medium after merging approaches a predetermined temperature.

A waste heat recovery device with a first heat medium side inlet; a first heat medium side outlet; a first heat medium flow path; a second heat medium side inlet; a second heat medium side outlet; a second heat medium flow path; a heat exchanger that exchanges heat between the first heat medium and second heat medium; an expansion tank in the first heat medium flow path; a bypass flow path that causes the first heat medium to flow and bypass the heat exchanger; and a mixer where the bypass flow path and first heat medium flow path merge together. The mixer is configured to adjust a ratio of a flow rate of the first heat medium in the bypass flow path and a flow rate of the first heat medium in the heat exchanger, such that the temperature of the first heat medium after merging approaches a predetermined temperature.

A heat exchanger which is used primarily in oil and gas operations to heat tanks of liquids, such as drilling mud, water, heavy oil or other such fluids from freezing or becoming too viscous to pump.