Tankless water heater load

[CDM]

I have a customer wanting to remove an existing water heater and install a new tankless water heater at his residence.
The service is 200 amps, the house is 1,750 sqr. ft., it is all electric, the largest existing load is the heat with two 50A breakers, it is 4 bed rooms with 2 full baths. The new tankless water heaters nameplate is 112.5A and will be fed by three 40A double pole breakers. This load seems like to much. Is this calculated at 100%?
Thanks

 

[luckylerado]

I have a customer wanting to remove an existing water heater and install a new tankless water heater at his residence.
The service is 200 amps, the house is 1,750 sqr. ft., it is all electric, the largest existing load is the heat with two 50A breakers, it is 4 bed rooms with 2 full baths. The new tankless water heaters nameplate is 112.5A and will be fed by three 40A double pole breakers. This load seems like to much. Is this calculated at 100%?
Thanks

When all 3 elements are heating, it will see the full load.

 

[augie47]

A "rough estimate" using Mike load calculator is 138 amps without the water heater so you will
be exceeding your 200 amp service.

 

[GoldDigger]

When all 3 elements are heating, it will see the full load.

And the circumstances under which it will see full load depend on the differential between the incoming water and the set point and the rate of flow.
You have to assume that at some point the temp will be set high (~140 degrees and up) while the incoming temperature is low (under 50 degrees) and someone is filling the bathtub at full flow. But at least it will not be continuous.

 

[junkhound]

Here, the poco (PSE), would not connect a new service with a 112 A tankless with less than 75kVA dist xfmr due to voltage drops for other customers on the same dist xfmr. Poco would likely charge for upgrading the xfmr. (note: had to downsize a tankless for an ADU I wired 2 years ago to avoid paying a few $K to poco for upgrading xfmr). POCO WILL know about the load after any neighbors complain about sags and flicker.

Scenario: Holiday or party time in winter or hot summer: Say there is 40A heating load, 2 ovens on with food, 60A, elect stove going, another 30A, say only 20A for misc. Somebody spills and you throw some wet things in the dryer, 25A. You decide to do some dishes before the meal to clear the kitchen up and tankless comes on for say only 15, 20 sec at a time: 200A breaker trips.

Also, does customer have any high power tools or a welder? No one happy when breaker trips when somebody is running the dryer, you are welding (often 60A draw) and the heat or AC is on.

Note:
HO should check rebates of local poco, PSE paid 100% of the hybrid elec WH cost when I replaced my 50G elec WH with hybrid. (poco even pays part of install cost up to $800 total here)

92K BTU/hr heats only 2 GPM for 90F rise (previous answer temp example), 2 different people taking showers will NOT like the results unless both have restricted shower heads.

In own home, have a small 30A tankless for barn sink that works great for just a sink.