Sharing a tankless water heater on two power meters

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Jeff Phillips

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Upper Peninsula, Michigan

I maintain a 10-unit apartment building that currently has a 30-gallon electric tank water heater inside each apartment and a 61 gallon natural gas water heater in the common area laundry room which is highly under utilized. I hate having to drain and flush out the sediment tanks inside the apartments like this, especially when there is new carpet. I reside in one of these apartments and if I linger in the shower longer the water goes cold. It really annoys me that when I use up 30 gallons I know we collectively have all paid the utility bills to retain 361 gallons of hot water ready on standby in this building at any given moment, paying for it to cool off and be re-heated 24/7, yet we can't use more than 30 gallons per person and we still have the water go cold while in the shower. This setup seems highly inefficient, wasteful, and ineffective.

One unique feature of this building is that every apartment has not one but TWO separate 125 amp rated electric meter sockets. Apparently decades ago the local power company had offered a discounted rate for electric water heaters which were rigged up with timers to primarily heat the water in off-peak hours. They haven't offered that discounted rate in many years, but buildings which were originally wired up to have separate meters for their water heaters like this are grandfathered in to have no billing fees for that second meter. So it's just a second meter with no extra charges but merely an itemized breakdown of their electrical usage for their water heater.

I note that many of the larger capacity tankless electric water heaters are intended to be wired to multiple 40 amp breakers or similar. Inside each breaker connects to a different internal heating element. When only a small flow rate is required, only one of these heating elements turns on. As more hot water is being consumed, additional heating elements on the additional breakers kick on as needed.

I'm wondering -- is there any way we could get a larger size tankless electric water heater and set it up to be shared between two adjoining apartments, with half of the heating elements inside wired up to one apartment's water heater electric meter, and the other half of the heating elements wired up to the other apartment's water heater electric meter? All the meters are fed off the same high-capacity service drop, so the same two phases are present on all of them. I realize this may be tricky from an electrical code compliance perspective as you would generally expect turning off all breakers in a breaker panel to have killed all of the power to the appliance. I'm wondering if there's a type of panel that could have bus bars for four phases, which really would be the same two phases repeated but two connected through meter socket A and two connected through meter socket B, so that you still would have all the shut offs in one panel somehow? Or would there be a way of doing this with two adjacent panels mounted together perhaps?

And, is there any way to load balance the two evenly? Obviously I wouldn't want the same heating element wired to the same one meter to always be first to kick on when only minimal flow rates are demanded, as then one of the two apartments would get the bulk of the electric bill for the water heater usage. I would need to have something controlling which heating element kicks on so as to distribute them evenly round robin style or similar.

Obviously I'd prefer to have less equipment to maintain so if I can get 5 larger tankless water heaters to run 10 apartments that would be preferred over having 10 of them. This would also mean each apartment would have the benefit of not only the 125 amp capacity it is able to supply, but also the 125 amp capacity of its neighboring partner apartment that shares a larger tankless water heater, if there's a way to set it up like this.

Might it perhaps be an easier approach to have two separate tankless water heaters plumbed together in tandem so one heats the water as much as it can and then it flows into the other one which heats it the rest of the way? This would make it easy to wire the two to two different electric meters. It would also give you more flow rate availability of hot water because each apartment could potentially consume not just its own supply capacity but also any excess capacity the neighboring apartment isn't using at that moment. For example, if one tenant is in the shower and another member of his/her family turns on a faucet, we might be approaching the limits of what a <125 amp tankless unit could handle on the coldest winter days when the incoming water temperature is very cold. But, having a unit with near double that capacity would be more than enough for both tenants as its unlikely that while in the shower people are turning on multiple faucets at the same time. All the unused capacity of one apartment becomes a benefit of extra surplus flow rate capacity to the neighboring apartment.

Curious if anyone else has ever tried to load-balance the electrical consumption of a tankless water heater between two differing electric meters for adjoining apartments before?

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Berkeley, CA
Look into an EEMax electric tank booster.

Or, a new single Sanden SanCO2 heat pump central water heater, with individual flow meters to allocate the electrical cost based on gallons used.

John Gayewski

In the Trades
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Tankless water heaters need descaled every six months. Some only every year. Have fun with that. Your better off where your at.

Turn the heat on your water heater up. I have a 40 gal. My son takes a bath, gf a shower and me a shower seperately. We still have enough hot water. It's kept at 130.

Your water heater doesn't loose heat at the rate you think it does. Six months a year(the heating season) any heat given off is taking from your heating load.


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If you collect a lot of solid sediment every 6 months, it sounds to me as if a filter on the incoming water would make sense.

Is what you drain out blackish water without visible particles, or do you have particles? If blackish, then that sounds like sulfate being converted to H2S. If that happens, there would be a smell.
Hey, wait a minute.

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