How do I tell what rating my electric box is? 150amp or 200amp

[Wcross]

I am looking at putting in a tank-less hot water heater and the model I want requires 200amp service. I know it is supposed to be on the breaker box somewhere but darned if I can find it.
Any help would be greatly appreciated.

[mongo]

1. I think you're a little confused.

But to tell what service you have in your whole house, look at the main breaker on the top of the panel.

But, what the water heater wants is a 20amp circuit (not 200), and it needs to be on a circuit of it's own. You have a few options.

If you are replacing an existing water heater, you need to know which particular breaker it goes to. Hopefully it is labeled. There is a number on the edge of the switch handle to tell you if it's a 15 or 20 amp circuit, but most likely it is 20amp. If the water heater runs on a 15amp circuit, and presuming it's the only thing on that circuit (which it should be), you can get a new 20amp breaker and just switch it out. But check the gauge on the wiring -- you may have to replace the entire wire from the box to the heater with a lower gauge to handle the excess load.

If you don't know which circuit breaker controls the water heater, you are going to need a friend to flip each breaker while you hold a test light or voltmeter accross the two leads of going into the water heater.

If you're unfamiliar with house wiring, I also strongly suggest going to the library and getting a book. None of it is really hard, but it is super-important that you know what you are doing.

Hope that helps.

[Wcross]

2. They recommend 200amp service.

The unit uses 3 40amp circuits and a minimum of 8 gauge wire (will take up to 6 gauge). My current water heater has a 30 amp breaker so I will have to replace that, add two more 40 amps and run new wiring.
I did look at the main and it is 200amp.

[mongo]

3. damn, that's a lot of juice

120amps -- wow. I've heard that these on-demand systems are supposed to be more energy efficient. I know they only run when the hot water is running, but you have to wonder. I wonder if there is a point where the tank is more economical as demand for hot water goes up -- like say if you were to try to install one of these in a restaurant where there are always dishes being washed, etc.

Hope you don't have electric heat too...

[Wcross]

5. Everything is electric.

The way this works is there are three separate heating elements. They only kick on when needed. It is all dependent on the temperature of the water coming in. I am thinking of installing a solar preheating tank (maybe) that would pre-heat the water to 70-80 degrees. I have to see what my electric bill does with the tankless alone. I live alone and heating 35 gallons of water to 120 degrees 24/7 doesn't seem too practical to me. I would have tried a timer for the tank heater but it would still have to heat up 35 gallons and my schedule is such that I use my shower at different times of the day depending on what day of the week it is.

[mongo]

8. What's going to happen

when the electric heat is on, there are towels in the washer on hot, the dryer is running and a cake is in the oven? Will you hit that 200amp limit and trigger the breaker?

Also, has your breaker box ever been replaced? In older homes, many times the breaker box is replaced - often with a higher capacity box, but the wire runing up the side of the house to the box is not heavy enough.

I'm just a jack of all trades handyman, not an electrician. I would urge you to consult with a pro.

[Wcross]

11. Its only on when I am drawing hot water.

I may run the heat and the shower at the same time. For my lifestyle it will work out.

[Briarius]

6. wow that's a lot of power!

Sounds like a your panel will support it, I just have to wonder if 120A is really more efficient that a regular heater. (if I weren't about to walk out the door I'd do the calculations :D, yea geek!)

[Wcross]

7. It is actually more efficient.

Endless hot water
Delivers 4.0 gallons per minute
Compact, lightweight and mounts on the wall
Over 95% efficient
Easy installation
Perfect for one major application at a time
Replaces a 40-gallon tank


They say the more you use it the less efficient it becomes of course. For my situation it will be great. I am single and live alone. 1 shower a day, two loads of laundry a week and some dishwashing.

[doc03]

4. Wow! My electric furnace/ heat pump only only takes a 60 and

a 30 amp. Do you live next to a nuclear plant?

[oneighty]

9. Interesting

I just did a Google search.

The power requirements of your system could even require a transformer upgrade on the street (area) where you live and you might have to pay for that too.

Also the savings you might gain are very small compared to your investment.

Hardly worth it.

180

[Floogeldy]

10. You're knowledgeable.

And thanks for responding to my "air conditioner on an extension cord" thread. :)

[oneighty]

12. AC

You are welcome of course.

How did the AC question work out for you?

180

[Wcross]

13. I disagree.

I have a fairly new transformer on the poll. I have run that type of power usage before (dryer,oven,electric heat, water heater and well pump) all at the same time. I will have to use power management to overcome any weakness.
This unit only runs when I am drawing hot water. There are three separate heating elements which turn on independently depending on how much hot water is needed. The key is the temperature of the incoming water to the unit. My well water is 60 degrees incoming. I will only require a 45 degree rise in temperature.
I am also looking into converting my water heater tank to a solar pre-heating system which should be able to increase the temperature of the incoming water to 75-80. I would only need a rise of 25 degrees.
As for my cost of the unit. I paid 508.00 delivered, I will need to buy 3 new breakers and 60 feet of 8 gauge wire. 600 dollars should be my total investment. Deduct the 300 dollar federal tax credit for the unit and it is a 300 dollar total investment. I can expect a minimum of 15% savings on my energy uses. I have seen figures of up to 25% depending on your water usage (the more you use the lower your savings).
In my particular case, I expect to save between 15 to 25 dollars a month. I should break even in 12 to 20 months.
With the solar preheat system I would expect even greater savings.

[oneighty]

14. Disagree if you want

I am quoting from a site on Google.

From my own experience in South Carolina I needed three phase 220 volt service to operate a ten horsepower electric motor. It was necessary for the power company to install a new transformer to cover the required power.Had it been less than ten horsepower I would have to had paid for the change over myself.

I really do not care one way or the other but I sure would check with the power company before installing such an expensive device.

Good luck.

180

[Wcross]

15. Thanks

I am just trying to cut down on my energy usage. Being single I hope it will save a bit of energy for me. I don't know if it would be all that great if I had a family of four living here. Having to heat 35 gallons of water 24/7 to take one shower a day and wash clothes once a week vs only heating it for a 3 minute shower might make a difference.
I will take your advice and consult a professional before I install it. It never hurts to be sure! (good thing there is a 30 day return policy!)

[Hissyspit]

16. Is this a robot sex thread?

Are those allowed?