Builder partner has a house with a 24-4 tankless electric water heater. It is mounted high in a closet off a bedroom. Homeowner complains about loudness, and she's right. 1st contactor is really noisy, and the heating element bangs and gurgles, especially right after water stops flowing. This happens several times per night even with no water use - unit keeps itself warm.

Tankless Co sent 4 new contactors under warranty, changed brand from Eaton to Cutler Hammer. They got the Hammer part right - I swapped one out and it is still just as loud.

Builder wrapped unit in lead lined soundproofing wrap and loosely boxed it in closed cell iso board - didn't do much good.

I've tentatively recommended having his trimcarpenter build a sealed box with open cell foam on the inside, but that'll cost several hundred bucks, and I could be wrong.

Two other same size / model units in that house don't seem nearly as loud.

Thoughts, anyone?

Thanks

I have a Seisco RA28, and use a drainback well pump, The only time I 'hear' the heater is when there is air in the pipes, before the water hits the hot elements and hisses. (very hard on the elements) I have reduced the outflow at the heater using a valve, so that only water reaches the heater, when the pump cycles on and off. Otherwise, my heater has worked without any problems! An electric kettle would overheat its elements, if not covered by water, when on.

Sounds like it may be an air bubble in the unit if it mounted so high it could be highest point in system so it will be very difficult to purge all the air out. You should not hear the elec elements at all, unless they are not fully submerged in water then you will hear vapor bubbles popping. If that's the case the elements will not last very long.