I recently got my very well working tankless gas water heater replaced by a Rheem ProTerra 50gal HPWH.

I feel the water heater consistently draws way too much power (I measure with CT clamps). Basically there are two operating conditions: Heater on (mostly compressor/fan running) and standby.

If the heater is in running state it sucks around 450W. But in standby (no compressor, no fan, no heat element, no water drawn, ...) it's still 30W.

This seems a lot to me. That's 0.72kWh/day or 263kWh/year, just standby! This could run a whole home lab. For reference, my previous tankless gas water heater drew 5W standby.

In absence of the water heater, the normal standby power of the whole house is ~200W of which ~100W goes to the fridge. 15% of the total standby consumption just for the HPWH really feel high.

Are there any ways I can try to cut down this standby power?

  • 3
    That's a question for the manufacturer. Commented Jun 6, 2023 at 6:47
  • 1
    I noticed the same thing on mine. I can't find any spot on the controls getting warm, so my assumption has been that the 30w is probably mostly making it in to the water anyway and thus a non-issue.
    – KMJ
    Commented Jun 6, 2023 at 16:43
  • Is it 30W, or 30VA?
    – bobflux
    Commented Jul 6, 2023 at 8:43
  • I suspect this may be the lower limit of the CT Clamp you are using. Care to share the model. Commented Mar 2 at 11:52
  • Why did you replace a very well working gas tankless WH? 30 W is a negligible base load. Commented Mar 2 at 17:19

3 Answers 3


But in standby it's still 30W.

That's ridiculously high.

Make sure you measured Watts and not VA.

Normally, for residential use, utility meters only bill real watts. But if you measure current with a clamp-meter and multiply by voltage, you get VA. Problem is, these modern appliances often include EMI filters, which contain capacitors, which draw current out of phase with voltage. This does not use actual Watts, but it does increase current and therefore VA.

To measure power used by anything that is not a resistor, you need a real wattmeter, for example a Killawatt.

For reference, my previous tankless gas water heater drew 5W standby.

That's also very high: to run a pressure sensor it should not use more than 0.1W.


Yes, get a timer controlled relay or have a relay controlled by a separate timer or there are DIN rail timers.

Then only power the device around the times it is needed.

A bit of experimentation will be needed to find the amount of "advance" time needed (06:15 or 06:45) so you can have a hot shower in the morning at say 7AM after the kids drained the hot water last evening...

Made a timer like this with a relay, a DIN rail timer which could be set different for the 7 days of the week. Worked very well for controlling my heating.


Review the water heater's settings for energy efficiency, explore timer options, and contact Rheem support for insights. Consider using smart plugs to cut power during non-use, and check for firmware updates that may address standby consumption.

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