Wire Tankless Electric from Two Sub-panels?

7 years ago

last modified: 7 years ago

Am considering upgrading my vacation home's old, giant, hot water heater to a tankless. Why heat water when I'm rarely there, right?

The water heater models I'm considering generally require 120 amps total, and are powered by three separate 40 amp circuits (each on its own dual pole 240v breaker with 8/2 grounded wire). This is within the capacity of the home's electrical service (upgraded by the prior owner for, um, indoor agricultural use). However, there's not enough room in either subpanel for 3 240v circuits. They're right next to each other, though, and there's enough empty space to use 2 40A circuits from 1 panel, and 1 40A circuit from the other.

Is there any reason why I shouldn't use the two sub-panels in this fashion? To my mind, the two-subpanel set up side by side is like having one large subpanel, but I am not a professional and wouldn't move forward with this without being 100% certain I'm OK.

Featured Answer

Ron Natalie

7 years ago

I assume that you're talking about the Rheem. Nothing really precludes you from putting the breakers in different panels. You just have to make sure you're not overloading either one individually.

One of those panels (or possibly both) are going to be fed by a breaker somewhere else (the simplest has the subpanel fed by a breaker in the main panel next to it). You need to assure yourself that you're not going to trip the feeder breaker with the circuits you have in the subpanel.

Sort by:Oldest

Comments (9)

greg_2015
7 years ago
If your only concern is the waste of energy (and $) of heating the water while you aren't there, then just turn your tank down (or off) when you leave.
Related Professionals
Clarksdale General Contractors · Jamestown General Contractors · Nashua General Contractors · Butte General Contractors · Hempstead Home Remodeling · Marinette Home Remodeling · Concord Home Remodeling · Liberal Home Remodeling · Lewiston Home Remodeling · Provo Home Remodeling · Charlotte Bathroom Remodelers · Webster Bathroom Remodelers · Santa Fe Bathroom Remodelers · Idaho Falls Bathroom Remodelers · Vancouver Bathroom Remodelers
Paul A.
Original Author
7 years ago
last modified: 7 years ago
Thanks, Ron. They are separately fed from the main and I would make sure they can each handle their load.

Way to not answer the question Greg. I need to replace it anyways and am looking at options. If you're not going to contribute to the topic of discussion please don't bother replying.
greg_2015
7 years ago
Wow. Your specific question was already answered, so I just thought I'd give you something else to consider that maybe you hadn't.

If it's not helpful, then you don't have to do it. I was just trying to being helpful.
Paul A.
Original Author
7 years ago
It's not helpful at all as it didn't address my issue. It's just obnoxious and irrelevant.
weedmeister
7 years ago
Not really irrelevant. I was going to suggest if you didn't have propane, an electric POU heater is an energy hog. Depending on your water temperature, it may not heat as well as you want while your meter is whirling away (only so much temperature rise through the unit). The less expensive alternative might be to use a smaller electric tank that you turn off and drain when not there.

I had a friend with a vacation home with two full baths and laundry. She only had a 20gl tank that was only active when occupied.
Ron Natalie
7 years ago
last modified: 7 years ago
This is not a POINT OF USE heater (those have much smaller power consumptions). He's talking about the 24 or 27 KW whole house unit. Anyway POU or not, the thing is still likely a win over a tanked heater. It takes about 18KWh to take 50 gallons of water up to temp. This thing will flow 50 gallons in about 15 minutes, and only using 7 KWh to do it.

The biggest gripe with these things is making sure you have the elecrical capacity both in Amps and in pole positions on your panel to run it. Paul says he has enough...
kudzu9
7 years ago
greg-

For what it's worth, I thought your comment was entirely appropriate. When asking for advice, an OP can always choose to ignore a comment without getting huffy about it not conforming to their precise mindset.
weedmeister
7 years ago
R: sorry. I tend to use POU generically to cover all the tankless units out there. I'll be more explicit in the future.