[Tutorials] How to measure the usage of a gas water heater


Staff member
[SIZE= 14pt]Introduction[/SIZE]
In the quest to measure energy use, the gas water heater presents a problem because there is nothing electrical or mechanical that can be measured to know when it consuming gas. Ideally a flow meter to track LP or natural gas use would be the desired choice since it directly measures the utilization. I have not stumbled over any LP flow meters, much less meters that have an automation interface.

[SIZE= 14pt]Water Temperature Measurement[/SIZE]
The first approach to measure the water heater operation was with a temperature sensor attached to the copper hot water outlet. A hose clamp was used to attach the sensor to the pipe for a positive transfer of heat from the pipe to the sensor. The hot water recalculates so as the tank temperature goes down so does the outlet temperature. When this is measured it shows the pattern of decay and then temperature rise with about 4 cycles per day. When looking at the rise time it showed about 30 minutes from when the water temperature started to rise to when it peaked. This is a reasonable approximation. This technique is feasible because of the recirc pump on the hot water brings the heated water to a place where it can be easily measured. It is not ideal because of the uncertainty of how long the gas is on before the temperature rises.

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