Water heaters are used in homes, businesses and just about any establishment having the need for heated water. A conventional water heater typically has at least one heating element or “heater,” such as a gas-fired and/or electric burner. Each water heater also typically has at least one thermostat or controller for controlling the heater. The controller often receives signals related to the temperature of the water within the water heater, oftentimes from a temperature sensor that is thermally engaged with the water in the water heater. In some instances, a water heater may operate in accordance with a first temperature set point and a second temperature set point. The difference between the first and second temperature set point may be referred to as the differential of the water heater.
When temperature signals from the temperature sensor indicate that the water temperature is below a first set point, for example, when the water temperature is below about 120° F., the controller turns on the heater and the water within the water heater begins to heat. After some time, the water temperature within the water heater will increase to a second set point, which, for example, may be about 140° F. At this point, the controller typically causes the heater to reduce its heat output or, alternatively, causes the heater to turn off. This heat cycle begins again when the water temperature within the water heater drops below the first set point.
Typically, the temperature sensor protrudes into and thermally engages the water in the water heater. Sometimes, the sensor is disposed within a metallic well such as a brass, copper or combination of brass and copper well that itself protrudes into and directly engages the water in the water heater. Because metals such as brass and copper have high coefficients of thermal conductivity, the brass or copper well is efficient at conducting thermal energy from the water to the temperature sensor. Therefore, the temperature sensor can provide a temperature signal that closely tracks the actual water temperature within the water heater. Some temperature sensors, such as in electric water heaters, may be in direct contact with the water.
While metallic wells such as brass wells provide good thermal conductivity between the temperature sensor and the water within the water heater, they can be relatively expensive. Thus, there is a need for a water heater that has a less expensive temperature sensor configuration.