[OPharbor]

I'm looking into installing a new tankless water heater for my entire home. I have a 200 amp service, and the unit I'm looking at is 28kw. Would it be better for me to install the 4 30amp two pole breakers that the manufacturer specs. Or should I run a 120 amp into sub panel and then to the 4 breakers. It seems to me that using a subpanel will be more expensive, but a cleaner way to do it. Any suggestions? And what does anyone think of the tankless solution?

[tkrussell]

Since 28 KW is 116.67 amps, the feeder to a subpanel to handle the four breakers the manufacturers calls for, the feeder needs to be rated 25 % more than the connected load, so 116.67 * 125% = 145 amps. Round up to nearest standard size, so the feeder breaker needs to be 150 amp, and the feeder conductor can be no smaller than #1 copper or #2/0 aluminum.

Depending on the length of the 30 amp branch circuits, and the cost of a 150 amp breaker, which cannot be simply added to a 200 amp panel, the new 150 amp panel, and 150 amp feeder, it may be simpler to ust run the four 30 amp branch circuit cables and plug in 4 - 30 amp breakers into the Main panel.

At some point in time, all four 30 amp circuits will be calling for power and applying the total 116 amps to the main service. Are you sure the existing 200 amp service is sized to handle the existing load plus this additional 116 amps?

[Missouri Bound]

OPharbor... OK... as usual tkrussell has answered your question perfectly with many points to consider. But I have a question for you... why in the hell would anyone want an electric tankless water heater? They are energy hogs, and work very poorly in any restricted faucet or shower senario. (just my experienced opinion)

[Stratmando]

Both above post are great, giving up 8 spaces may not be an option, I like the Sub panel with the 4 breakers(personal thing), also makes a good disconnect for the 4 breakers.
I am also not sold on the Tankless water heaters. Fixed many.
Old style, I changed elements and thermostats are easy and cheap, with a blanket and timer, they can be more efficient.

[Missouri Bound]

So often I hear that a conventional water heater "wastes" energy by heating water when there is no demand. I had my boiler replaced a few years ago, and they began at 8 AM. They had to disconnect the water heater at that time. They finished at 6 PM the same day and when they left I lit my water heater... it didn't fire up when I turned it from pilot to heat. I thought something was wrong... but actually in the 10 hours it was idle, and no hot water was used... the temperature didn't drop to fire the burner. I turned on the tap for hot water and it was hot... and shortly after the water heater fired as usual. I see no reason for switching to tankless water heaters.

[OPharbor]

OPharbor.....OK...as usual tkrussell has answered your question perfectly with many points to consider. But I have a question for you....why in the hell would anyone want an electric tankless water heater? They are energy hogs, and work very poorly in any restricted faucet or shower senario. (just my experienced opinion)

Thank everyone for your help. The tankless option has been troubling me for some time. My thinking is, unless I go to gas, which I do not have available, meaning I'd have to add a propane tank and ventillation, a more energy efficient conventional meodel, may be a better option.

[Stratmando]

They do make Gas Tankless water heaters. Look through here:
http://www.geconsumerproducts.com/pr...lesshybrid.htm
And
http://www.chilipepperapp.com/tankless.htm

[OPharbor]

They do make Gas Tankless water heaters.

Yes, I was looking a Rinnai (sp), but again the cost of installing a propane tank and ventillation is just not worth it. They are also less energy effieicnet than electric. I looked at some specs on tankless that quoted a 18-20 year rate of return, I may not even live that long! :)

[Stratmando]

In 18 -20 years, you will likely have replaced it a couple of times.