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I purchased a tankless waterheater. It uses 100 amps. I called an electrician to get a price to hook it up. He stated that I only have a 100 amp entrance and the only way to make the heater work would be to upgrade my service. I called and spoke with the manufacturer of the heater and stated my problem and wanted to return the item. He states that I can install a sub-panel in a way that I can still use the heater. Does anyone know if this is true? I would really like to use the heater but not at a fire risk. thank you
 

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100a tankless with a 100a main

Sure that will work, as long as you don't want to use ANY other electric in the house

Send it back or upgrade your service
 

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what he's telling me, I gather, is that if I hook it up correctly, I will have a 100 amp main box and a 100 amp sub-box, which will give me plenty of amps and the water heater will never affect the main box. sounds true? maybe not though.
 

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Woody- If you only have 100a MAX to start with and you use a full 100a for the water heater (whether from the original box or a subpanel), you have NONE LEFT! No matter how it is hooked up you can't get more than you started with! More panels do not allow more amperage! The "weak link" or restriction is the amount of amperage coming thru your meter and main breaker.

When the heater is off you would be fine, if you were watching tv, eating dinner, running the dishwasher etc and the heater kicks in, the house would likely black out due to the main breaker overload.
 

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Nothing prevents you from installing a 100 amp. subpanel with the idea in the back of your mind of upgrading your electrical service in the future.

At the main panel you would have a pair of 100 amp branch circuit breakers to feed that subpanel. If the water heater is the only thing on that line, you don't need a subpanel since the same 100 amp breakers could protect a home run to the heater.

Any subpanel hanging off the main panel does affect the main panel in terms of current drawn.

If your main panel won't accommodate 100 amp branch circuit breakers, you would have to use a lesser breaker for the subpanel temporarily (and not use that water heater) until you upgrade your main panel and service.
 

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thats what i thought. he tells me i have more amps coming into the house but only 100 coming out of the box, so if I hook up the sub panel before the box, or at the begining i will be able to use more, guess it was more wishfull thinking
 

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thats what i thought. he tells me i have more amps coming into the house but only 100 coming out of the box, so if I hook up the sub panel before the box, or at the begining i will be able to use more, guess it was more wishfull thinking
True, if your house is set up just right, and all the planets aline in perfect order.
Chances are slim that any house is set up right for this install.
 

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thats what i thought. he tells me i have more amps coming into the house but only 100 coming out of the box, so if I hook up the sub panel before the box, or at the begining i will be able to use more, guess it was more wishfull thinking

IF there is a 200a disconnect somewhere outside then you have access to more power. But if you have 100a service then this will NOT work. Call you electric Co or consult with an electrician to determine the power to your house
 

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guess I'm still confused. with the 100 amp branch circuit breaker, will this work
Tell us the manufacturer of this tankless heater and the model # and if they have a web site I'll show you why this will not work on a 100 amp mains service.
 

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guess I'm still confused. with the 100 amp branch circuit breaker, will this work
This will help:

Think of it this way:

Your main panel is like a library; it is a 100 Amp size library, so it has 100 Amps of "books" it can loan out at any one time.

Most of the time, your home "borrows" / uses maybe 30 to 50 amps (30 to 50 books) at one time. If your house is using 50 of the amps (50 books), there are only 50 left (50 books left).

Your new water heater wants to borrow 100 Amps (all 100 books) all on it's own. If you only have 50 Amps (books) left in your library, where are the other 50 Amps (books) going to come from????

The answer is they are NOT going to come from that main 100A panel, regardless of sub panels or other fancy setups, it defies basic electrical principals.

If you connect it anyway, what is going to happen when the water heater starts running is you will open (trip) your main breaker due to drawing too much current at one time. This will disable power to your entire home leaving you in the dark until you reset the breaker, and the process will be repeated until the water heater is removed or the main service panel is upgraded so it has more amps "books" to loan out at any given time.

I hope this was useful and didn't seem condescending, it was only intended to be helpful

Jamie
 

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guess I'm still confused. with the 100 amp branch circuit breaker, will this work
Read post # 2.



The only only real answer is, no...it won't work.


One person said sarcastically that it will work if you don't use any other power.

Someone else may have suggested that it would function but would not be safe.

There is no way in hell that you can safely add a 100 amp load like that to a 100 amp service. The math is as simple as it sounds in this case.
 

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water heater energy usage

40 Therms/mon = 1200 kwH/mon = 1.7 kw continuously ("7 amp service") vs.
24kw ("100 amp service") for a short time.
This is a 7% duty cycle at 100A.

You need energy storage or an electrical upgrade.

I don't know why anyone would want one of these. You don't lose very much with tank heaters, and these tankless things click a lot and do not anticipate shower water demands.
 

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Mmm, I wonder if these electric tankless salesmen will ever be held accountable for their actions.

Hear Hear !! I wish they used thier brain little more and do the figures.

few manufacters now getting smart they start to list a warning about service size most larger tankless heater will required a min of 200 amp service and it is common to see them run on 320 amp { 400 amp max 320 contiouns } or resort to three phase service then it will slove that dammed thing.

Really honestly I allready work on few tankless water heater both North America and European side and all of them boil down is the service size that what useally seal the fate on them.

For anyone want the tankless waterheater ya better do the figures carefully there is a whole house verison and point of use verison that will make the diffrence there.

Merci,Marc
 
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