Tankless Electric Water heater and 150 amp service

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Greg1707

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Location
Alexandria, VA
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Business owner Electrical contractor
I have a customer with an all electric 1,800 square foot condo with a 150 amp service.

The customer wants a tankless water heater. The specifications show the unit needs 150 amps.

This brings up a question. If a house has gas then the obvious choice is to use a gas powered water heater tankless or tanked.

That leaves electric tankless units suitable only for electric only houses. So, if a house is all electric, what size service would be needed for a tankless water heater?

In what scenario are these units practical?
 
Greg1707 said:
That leaves electric tankless units suitable only for electric only houses. So, if a house is all electric, what size service would be needed for a tankless water heater?

In what scenario are these units practical?
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Regardless of the service size you would need to do a load calculation to determine if the service is large enough. How many amps is the water heater?
 
infinity said:
Regardless of the service size you would need to do a load calculation to determine if the service is large enough. How many amps is the water heater?
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Ok. The electric furnace is on a 70 amp breaker. Plus range, dryer, microwave etc.
 
Greg1707 said:
Ok. The electric furnace is on a 70 amp breaker. Plus range, dryer, microwave etc.
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Take a look at art 220 then come back with any questions you have.

Depending on how much temp rise is needed and how much flow is desired, you possibly take up most your existing 150 amp supply easily with that water heater.
 
My post was meant to be a more general observation. Of course, I can do a load calculation. And it is obvious that a 150 amp tankless water heater will not work with a 150 or 200 amp service. My observation is that these units seem to be impractical in my area where the largest service (typically) is 200 amps.
 
Greg1707 said:
My post was meant to be a more general observation. Of course, I can do a load calculation. And it is obvious that a 150 amp tankless water heater will not work with a 150 or 200 amp service. My observation is that these units seem to be impractical in my area where the largest service (typically) is 200 amps.
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They are kind of impractical in most applications. They are relatively inexpensive making them attractive to home owners to purchase their own, along with the not heating unless there is hot water demand, then find out what kind of cost the electrical will bring to make it work is a big surprise to them. They don't just simply connect to what was there before like maybe owner was thinking.

Point of use types at say a hand washing sink is about the only practical application I have encountered.
 
I don't think this is a good combination for a solar powered battery backup system unless you can switch your whole house the grid when you want hot water. A load of 150a will probably kick your Tesla system off into a 'wait for restart' mode and likely it won't start until you kill that load. And even if it continued to run, that kind of load would drain your battery in no time at all. We have somewhat the same situation and we use a GE gas-fired vertical tank hot water heater and it doesn't take any power from the battery....we run our stove on this same propane and one large bottle lasts about 3 months. I'd consider a tankless gas fired unit if this one dies...my neighbor has one and he likes it a lot and it doesn't waste gas keeping a tank of water hot. Plus, the initial cost is less than a tank model. Same applies to a clothes dryer. Think 'moving heat'=electricity.
 
ptonsparky said:
FWIW, a customer called me about an electric tankless years ago. I told him his 150 service was insufficient. He had already installed it himself, but had questions of some sort. He used it for years. All electric home, three women in the house.
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Sometimes you get lucky!
 
Electric is fine stateside, but we have a much bigger, much more irritating and unreliable PoCo down here. They are totally undependable, and will go on, or brownout, or off with no notice. One of the main reasons we went Tesla 4 years ago. Bottled gas is reliably available and they will deliver the same day or early next day, without fail. Ergo, gas stove and calentadora de agua (water heater). I wish we had a gas clothes dryer but the over/under model we have doesn't come in gas, so for that ONE item, we switch the whole house directly to the grid (not through the gateway) , dry the clothes and back to the Tesla.
 
ptonsparky said:
Exactly what I told him.
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Having an FPE breaker that won't trip isn't necessarily lucky? ;)

One probably can get away with this more often than you might think though. Really depends on other loads and habits of the users. That 150 amp main probably does see more than 150 amps at times but never for long enough to make it trip.
 
kwired said:
Having an FPE breaker that won't trip isn't necessarily lucky? ;)

One probably can get away with this more often than you might think though. Really depends on other loads and habits of the users. That 150 amp main probably does see more than 150 amps at times but never for long enough to make it trip.
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Just shows how conservative code calculation for a Service entrance is.
 
Greg1707 said:
I have a customer with an all electric 1,800 square foot condo with a 150 amp service.

The customer wants a tankless water heater. The specifications show the unit needs 150 amps.

This brings up a question. If a house has gas then the obvious choice is to use a gas powered water heater tankless or tanked.

That leaves electric tankless units suitable only for electric only houses. So, if a house is all electric, what size service would be needed for a tankless water heater?

In what scenario are these units practical?
Click to expand...

Often times you would have to upgrade to 400 amps or even more depending on the size of the heat strips. Condos are not very realistic to install electric instant water heaters as you cannot easily upgrade services.
 
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