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I replaced a tankless water heater with the same model, but a couple of years newer. (The original was damaged by careless house painters). This is a 13 kw Rheem unit and on its own circuit.

Since that time, when we run the hot water in any location and turn on the induction stovetop or larger overhead ceiling fan, we hear a very noticeable hum. This was not apparent with the earlier tankless. We've had professionals come over and tell us that it looks good from an electrical perspective and to call an appliance repair shop. Any suggestions?

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  • Can you tell where hum is coming from? Is new heater same specs as old, did you happen to check?
    – crip659
    Mar 17, 2021 at 13:59
  • Can you provide the exact model number? (Edit it into your original post.)
    – FreeMan
    Mar 17, 2021 at 14:11
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    Did your “pro” put a power analyzer on the main? With your newer water heater it could be using solid state control. Most solid state control creates harmonics on the power line. The harmonics may be affecting the stove top and fan, it may be worse in the stove top as induction units also convert the 60hz to a higher frequency and are a large load. But that’s what I would be looking at, contacting Rheem and talking with them about excessive electrical noise may get a response.
    – Ed Beal
    Mar 17, 2021 at 15:37
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    Agreed with EdBeal that contacting Rheem about it would be a good idea. The fact that it's causing audible noise in other electronics very likely means it's putting out a whole lot of RF noise as well, and likely violating their FCC emissions rating. There's a good chance it's just a defective unit, and they may well replace it under warranty.
    – Nate S.
    Mar 25, 2021 at 16:43
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    is it the stovetop that is making the noise when you run hot water? I also have a Rheem tankless water heater and we just got a new induction stove top. Whenever I am cooking and run the hot water at the same time, my stovetop burner buzzes. Feb 8 at 13:53

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The problem is probably that the new unit uses solid-state control to vary the power delivered to the heating elements, which makes it more energy-efficient than the old-fashioned on/off control. Those solid-state controllers are notorious for introducing harmonic "noise" on the mains, and a 13 kW one could easily affect other circuits fed from the same main breaker panel. Resistive loads like heaters and incandescent lights aren't affected much, but loud humming from magnetic/inductive loads is textbook harmonic interference.

The first thing I'd try is complain to Rheem about excessive harmonic noise. An expensive brand-name water heater should have some built-in EMI (Electro-Magnetic Interference) filtering to minimize the effect. If it's making your induction stove sing, it's definitely "excessive" harmonics, and it might possibly even damage sensitive electronics plugged in elsewhere in the house. (That's not very likely, but is technically possible, and if needed it might make a useful line of argument to get Rheem motivated to take you seriously.)

The traditional way to eliminate harmonic interference (used with industrial VFD variable-frequency motor controllers, for example) is to connect the "noisy load" (your water heater) via a harmonic filter or isolation transformer. That's very effective, but I can't say I've ever seen a 13 kW harmonic isolation transformer marketed toward residential use... and the cost may be prohibitive. Industrial electrical suppliers and data-center power-supply companies are the obvious place to start looking if you go that route.

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