Tankless water heater referral

[Greg1707]

I have a HVAC/Plumbing contractor that provides me with considerable amount of work. When their customer needs electrical work for a new AC unit or mini split I get the call. They are working with a customer to install a tankless electric water heater. The unit needs 3 forty amp circuits.

The house is an all electric (200 AMP) very large townhouse with two heat pumps, hot tub, electric range etc. I can make space in the panel by using piggy back breakers.

The run from the panel to the water heater will need 250' 8-2 NM.

This is a town house community so a 400 amp service is not possible.

Should I have any concerns about this project?

 

[infinity]

Should I have any concerns about this project?

I would be concerned that the current 200 amp service isn't large enough.

 

[petersonra]

This is a town house community so a 400 amp service is not possible.

So what does one do if the calculated load exceeds 200 A? Is the homeowner just out of luck?

I would do the load calculation and see if it works. Keep in mind 220.83 or 220.87 might be your best friend.

 

[LarryFine]

The run from the panel to the water heater will need 250' 8-2 NM.

That's a heck of a run. Are there any alternative sources?

Should I have any concerns about this project?

I would. I suggest starting with a realistic load calc.

 

[LarryFine]

So what does one do if the calculated load exceeds 200 A? Is the homeowner just out of luck?

Yep, if there's no gas. Or, just connect it anyway and tell them how to minimize tripping the main.

 

[Greg1707]

That's a heck of a run. Are there any alternative sources?


I would. I suggest starting with a realistic load calc.

250 feet for 3 runs

 

[LarryFine]

250 feet for 3 runs

I would run a single feeder to a sub-panel instead; you'll need local disconnects anyway.

This would be way more economical, be easier to install, and present no derating concerns.

 

[Greg1707]

I would run a single feeder to a sub-panel instead; you'll need local disconnects anyway.

This would be way more economical, be easier to install, and present no derating concerns.

Larry
3 runs x 80 feet equals 250 feet

 

[winnie]

So what does one do if the calculated load exceeds 200 A? Is the homeowner just out of luck?

There are things such as energy storage or load shedding systems which might be considered, but realistically if you want to store energy for water heating it might as well be stored in the form of hot water.

I would go with a heat pump tank water heater rather than a resistance tankless. Gas tankless beats them all.

 

[don_resqcapt19]

Even if the service is large enough they and their neighbors won't be happy with the light flickering as the heat kicks on and off.

 

[LarryFine]

Larry
3 runs x 80 feet equals 250 feet

D-oh! That got past me.

Still, the reasoning applies even for 80' and for disconnecting.

 

[James L]

I wonder if it's a multi-stage water heater?
Seems likely based on the multiple circuits

It may not be as big an issue as it appears, if they're not using 3 showers at once

 

[LarryFine]

Still, the reasoning applies even for 80' and for disconnecting.

What I mean is 1 x 120a worth of feeder and a panel vs 3 x 40a worth of circuits and three disconnects.

 

[AC\DC]

Electric tank less suck, if you actually put in the proper temperature for the calculations your going to need a monster. Gas is another story..

I never understand why people like these beside taking up less room. Just a dump unit and expensive to repair and longevity is no longer than a tank unit.

 

[brantmacga]

Electric tank less suck, if you actually put in the proper temperature for the calculations your going to need a monster. Gas is another story..

I never understand why people like these beside taking up less room. Just a dump unit and expensive to repair and longevity is no longer than a tank unit.

I have to agree. I’ve provided electrical for maybe 4 of these things and all of them required a service upgrade. One of them was for a good friend of mine, who I did try to talk out of it, and he’s had multiple part failures over the last 5 years or so since installing.

We swapped our electric tank to gas tankless 4 years ago and while it works great, the gas bill just doesn’t seem worthless. I’m thinking about going to a heat pump tank when we rebuild our house.


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