Following 2020 and next NEC changes, is the tankless water heater CONTINUOUS load or not.

[AlxLnv]

There is the question which is a little unclear, are the tankless water heaters or the steamers a continuous load or not? According to the Mike Holt forum thread, the answer was it is not, which question was closed by the Moderator in 2020. Now I met the same question.
I finished the New Jersey Ocean County Vocational School with Electrical Apprentice certificate in 2008. Since 2008 the NEC got charged several times. If in 2002 the tankless water heaters were not popular, today they are on sales in Home Depot.
If calculate non-continuous load it would be less OCDP rating and smaller wire size. With Continuous load the 125% add breaker rating and wire size. For example, 69 Amp nameplate refer that the wire may be AWG 6 of THHN or exual from 90°C for 75 ampacity instead of AWG 4 in case of continuous load, that will need to increase Ampacity to 95 amp, and breaker to 90 Amp.
I remember that in my sister's house they changed their water tank into tankless and when they turn on the hot water the kitchen lights were blinking.
Theoretically, the water heater MAY BE WORKING FOR THREE HOURS and longer. The relatives are visiting house and taking shower one after another one.
By the life experience it may be very unusual.
The old forum do not clear out if it is NON-CONTINUOUS or it is CONTINUOUS load. I think the new NEC should have the stipulations about.

 

[infinity]

There is the question which is a little unclear, are the tankless water heaters or the steamers a continuous load or not?

No they're not by the Article 100 definition of continuous load..

Welcome to the Forum.

 

[AlxLnv]

No they're not by the Article 100 definition of continuous load..

Welcome to the Forum.

Thank you.
I understood that definition has "EXPECTED" word that means the light in commercial buildings will be more that 3 hours. That definition may be equal the word "scheduled".
So, the water heater are not "expected" to be working continuously longer 3 hours or are not be "scheduled" for the working longer that 3 hours.
Thank you very much.

 

[suemarkp]

Most of them also have staged heating elements and with higher water flow more elements kick in. So you could still use it on a regular basis for 3+ hours and have it not be a continuous load if not all of the elements are on for that use case (e.g. heater is designed to make sufficient hot water to 6 GPM. Use it at 3 GPM for a 4 hour process and it isn't continuous).

 

[infinity]

Most of them also have staged heating elements and with higher water flow more elements kick in. So you could still use it on a regular basis for 3+ hours and have it not be a continuous load if not all of the elements are on for that use case (e.g. heater is designed to make sufficient hot water to 6 GPM. Use it at 3 GPM for a 4 hour process and it isn't continuous).

Exactly. The definition of continuous load has two components, one being for 3 hours or more and two that the load has to be at maximum current for those 3 or more hours. An instant hot with some type of thermostatic control would not be a continuous load because it would cycle on/off during those 3 hours. As you've mentioned if it ran for more than 3 hours but at a reduced current level then it also is not a continuous load because it doesn't meet both of the required conditions in the Article 100 definition.

 

[roger]

Theoretically, the water heater MAY BE WORKING FOR THREE HOURS and longer. The relatives are visiting house and taking shower one after another one.

Well unless they are getting in the shower before another leaves it would still be non-continuous. If they are in fact getting into the shower while another is in it they probably have bigger issues than the water heater

 

[Little Bill]

Exactly. The definition of continuous load has two components, one being for 3 hours or more and two that the load has to be at maximum current for those 3 or more hours. An instant hot with some type of thermostatic control would not be a continuous load because it would cycle on/off during those 3 hours. As you've mentioned if it ran for more than 3 hours but at a reduced current level then it also is not a continuous load because it doesn't meet both of the required conditions in the Article 100 definition.

I wonder why a WH with a tank is considered continuous? Both elements are never on at the same time.

 

[LarryFine]

I wonder why a WH with a tank is considered continuous? Both elements are never on at the same time.

True, but just to point it out, that means it's still at its full load whenever it's on.

 

[Little Bill]

True, but just to point it out, that means it's still at its full load whenever it's on.

But there is a moment where it switches elements. That would stop the continuous load, if only for a second or two.

 

[Hv&Lv]

I wonder why a WH with a tank is considered continuous? Both elements are never on at the same time.

Even with one element in at a time I wondered the same thing. About an hour to heat 40 gallons..
That's a lot of hot water to stay on continuous for three hours..
Then again, I don't have four daughters living at home.

 

[GoldDigger]

Most critically, the demand, actual shower time, can be intermittent but can still cause the WH element to be on continuously because of its storage nature. And the elements are continuously operating at full load rather than tapering off their current draw as the tank approaches full water temperature throughout
One person every hour for three hours taking a shower that lasts until the hot water runs out will lead to an over 3 hour continuous load.

 

[Little Bill]

Most critically, the demand, actual shower time, can be intermittent but can still cause the WH element to be on continuously because of its storage nature. And the elements are continuously operating at full load rather than tapering off their current draw as the tank approaches full water temperature throughout
One person every hour for three hours taking a shower that lasts until the hot water runs out will lead to an over 3 hour continuous load.

I guess we would look for the most wrinkled/swiveled up persons to blame for this!
I can see if other water was being used at the time, that one would run out of hot water. But I've never seen a person that used all of a 40 or 50 Gal tank of hot water on a single shower.

 

[augie47]

"most wrinkled/swiveled up person"
you rang ??

 

[Little Bill]

"most wrinkled/swiveled up person"
you rang ??

Glad you're awake. Now go take a shower!

 

[tortuga]

I remember that in my sister's house they changed their water tank into tankless and when they turn on the hot water the kitchen lights were blinking.

This is pretty common with on-demand water heaters and LED lighting on dimmers, to the point that I wont even troubleshoot it.
The last one I looked at look at the kva of the water heater was 27 and the kva of the utility transformer for the 4 houses on the block was 25.
These things rely on the fact that utility transformers can handle about 2X their nameplate for a short time about a 1/2 hour, so if you ever ran one continuously you would likely blow the transformer.
I will say they are very popular with vacation type short term rentals where you might have 12 people crammed in house for 3 days then nothing for a week.
The POCO hates these things, an alternative I have found is a 'simultaneous' water heater, where you run two 30A circuits so both elements can run during recovery, but that does not save any energy when the house is empty for long periods of time.

 

[retirede]

I guess we would look for the most wrinkled/swiveled up persons to blame for this!
I can see if other water was being used at the time, that one would run out of hot water. But I've never seen a person that used all of a 40 or 50 Gal tank of hot water on a single shower.

Our first house had a 50 gallon electric. My youngest daughter would shower until she ran out of hot water.
We moved to a house with tandem 40 gallon gas. I don’t know how long her first shower was, but the water never got cold.