# Tankless Water Heater Install



## ronjon1702 (Nov 22, 2010)

Im installing a new electric tankless water heater and have a couple questions. Im mainly concerned about the electical part. The water heater requires 3 50 amp 240 volt lines run to it. So what i decided to do was run these 3 lines(6-3 wire) out of a sub panel. I got me a 125 amp load center and put the 3 50 amp breakers into it.What I need to know is what size breaker to install off the main service panel(200 amp service) and what wire to run from the main service panel to the sub panel. The sub panel is about 15 feet away from the main service panel. I have 2-2-2 aluminum wire that I thought i could use to run from the main service panel to the sub panel but I think im missing a wire and still dont know the size of the breaker. Let me know what you think.


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## Speedy Petey (Sep 30, 2003)

A) You only need 6/2 wire for this.
B) If the unit requires three 50A circuits the draw on each is likely 35-40 amps.
C) #2al can support a 100A sub-panel in some cases, a 90A in others (depending on the jurisdiction).
D) Do the math.

An on demand heater that requires those circuits is absurd to install in the average home IMO. With a 200A service, if you do decide to install this massive unit you are almost certainly going to need a service upgrade to 320/400A. 
2/3 of your 200A service is going to be taken up by this stupid thing.

Do you get the impression that I think whole house electric on demand water heaters are crazy?

Don't forget, the energy savings are minimal and the installation costs are massive.


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## ronjon1702 (Nov 22, 2010)

Speedy Petey said:


> A) You only need 6/2 wire for this.
> B) If the unit requires three 50A circuits the draw on each is likely 35-40 amps.
> C) #2al can support a 100A sub-panel in some cases, a 90A in others (depending on the jurisdiction).
> D) Do the math.
> ...


 
I am agreeing with you that these water heaters are crazy but thats a different topic. 

So in answering my question you are saying I can put a 100 amp breaker into my Main service panel and this will adequetly feed my sub panel that has the 3 50 amp circuits? How do i use the 2-2-2 wire to feed my sub panel?


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## Speedy Petey (Sep 30, 2003)

ronjon1702 said:


> So in answering my question you are saying I can put a 100 amp breaker into my Main service panel and this will adequetly feed my sub panel that has the 3 50 amp circuits?


No, I am not saying that at all. It is certainly NOT adequate.
You more than likely need a 150A sub-panel which typically cannon be had from a residential 200A main panel.




ronjon1702 said:


> How do i use the 2-2-2 wire to feed my sub panel?


Personally, I feel if you have to ask this question this way you should seriously consider having an electrician do this for you rather than a plumber feeling your way through and just making it work.


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## ronjon1702 (Nov 22, 2010)

Speedy Petey said:


> No, I am not saying that at all. It is certainly NOT adequate.
> You more than likely need a 150A sub-panel which typically cannon be had from a residential 200A main panel.
> 
> 
> Personally, I feel if you have to ask this question this way you should seriously consider having an electrician do this for you rather than a plumber feeling your way through and just making it work.


 
This is an excellent point you make but whats wrong with double checking with the likes of an electrician before I complete the install? Ive talked to multiple electricians all of them say I can install this on a sub panel so whom am I to believe?


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## Speedy Petey (Sep 30, 2003)

Of course you can install it. It is likely not enough to power this unit though. 

Do you have the actual specs?


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## ronjon1702 (Nov 22, 2010)

Speedy Petey said:


> Of course you can install it. It is likely not enough to power this unit though.
> 
> Do you have the actual specs?


here is the technical data. I have the tempra 29
stiebel-eltron-usa.com/techdata_tempranew.html

here is the install manual

stiebel-eltron-usa.com/pdf/install_tempra_tempraplus.pdf


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## Speedy Petey (Sep 30, 2003)

Yup, that thing is 28.8kW. That is 120 amps at 240v full blast. 

NO WAY it is going to run on a 100A sub-feed and a 125A sub-feed is marginal at best.
For a 125A sub-feed you would need 1/0cu NM or SER cable, or #1cu individual conductors in conduit.


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## ronjon1702 (Nov 22, 2010)

Speedy Petey said:


> Yup, that thing is 28.8kW. That is 120 amps at 240v full blast.
> 
> NO WAY it is going to run on a 100A sub-feed and a 125A sub-feed is marginal at best.
> For a 125A sub-feed you would need 1/0cu NM or SER cable, or #1cu individual conductors in conduit.


 
Now we are getting somewhere! So not even a 2-2-2-4 Alum SER would do the trick? I assume i just put a 125 amp breaker in my main service panel and that will feed my subpanel?


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## Speedy Petey (Sep 30, 2003)

ronjon1702 said:


> I assume i just put a 125 amp breaker in my main service panel and that will feed my subpanel?


Well, yes, but it's not quite that simple.


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## ronjon1702 (Nov 22, 2010)

Speedy Petey said:


> Well, yes, but it's not quite that simple.


 
And that 2-2-2-4 cable wont work?


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## Speedy Petey (Sep 30, 2003)

........


Speedy Petey said:


> For a 125A sub-feed you would need 1/0cu NM or SER cable, or #1cu individual conductors in conduit.


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## John Valdes (Apr 14, 2010)

Well here comes your second licensed electrical contractor to tell you you do not have enough with the 200 amp main to do this right. While you could install the breaker and feeder for the water heater, you will overload the system. Your main is going to trip if the demand gets great enough. Like this Thursday, when everyone is at your house for Thanksgiving dinner. See the point?

Call one of those guys (electricians) that told you it was okay. Have them install the sub and the demand water heater and then make them give you a guaranty. See if you can find a taker. Make sure its in writing if you do find one.

I suggest you upgrade your service or return the demand unit and get a tank model.


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## ronjon1702 (Nov 22, 2010)

Ill let you guys know how it goes......


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## stars13bars2 (Feb 13, 2005)

Nooooo! Just don't hook up one of these. :no: You have never seen lights dim so badly , and the utility will want to know if you are using one of these as all the houses connected to the transformer will dim as well. People will be pizzed. :furious: :furious: :furious:


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## John Valdes (Apr 14, 2010)

One thing we have not mentioned is gas. A gas powered demand water heater is the only way to go with this type of water heater. If I had gas I would consider getting one myself.


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## PrestigeR&D (Jan 6, 2010)

*I'm picturing...*

fire engine trucks for some reason........ ... do yourself a favor... take it back... sell it,.,whatever... get a gas unit,,, don't risk it... you'll be sorry ... I'm no electrician but common sense would tell you not to do this..

B.


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## Speedy Petey (Sep 30, 2003)

stars13bars2 said:


> Nooooo! Just don't hook up one of these. :no: You have never seen lights dim so badly , and the utility will want to know if you are using one of these as all the houses connected to the transformer will dim as well. People will be pizzed. :furious: :furious: :furious:


I actually forgot about this aspect. 
I wired a tiny unit, only for one bath and required "only" two 40A-240v circuits. The lights did not only dim, but they actually pulsated. 
The f-ing plumber tried blaming on me. Even the manufacturer had heard of this happening, but had no explanation and also no excuse. 
The customer was PISSED since the room was on a slab with NO attic. They were stuck with it.


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## ronjon1702 (Nov 22, 2010)

Got this done about one week ago and I swear on the Internet Gods its works just fine. It does have issues with heating up the bathtub but i just slowed down the water pressure to the tub and it works pretty good. No dimming, no pulsating, no firetrucks(so far) but all in all im happy with the outcome. Its also the middle of winter, 7 degrees yesterday morning and took a shower with no problem. Total cost of the install was about 110 for all the electrical and another 30 for plumbing. The unit only cost 400. I even have it set on full blast and I still havent noticed any dimming. Thoughts?


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