I am installing a radiant heat system alongside a rocket mass heater. I want to compare the cost of operating each. For the radiant heat system, an on-demand electric hot water heater is being used. I want to meter power used by this device as a way to quantify the cost of operating it.

The heater will be hard-wired and operates on split-phase 240v at 19A. What's the best way to meter its actual power usage?

  • Google electric sub-metering
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    Commented Nov 21, 2016 at 0:16
  • There are many products available. I'm not confident in my ability to select the right one for my project. A little bit of hand-holding would be appreciated. :) Commented Nov 21, 2016 at 13:22

1 Answer 1


I went with a 120/240 Volt Pass-Through kWh Meter, 3-wire (2 hots, 1 neutral), 100A, 60Hz, EKM-25IDS.

The meter is hard-wired in front of the hot water heater and provides a digital kWh readout for the hot water heater's power usage.

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