# on demand water heaters, am I missing something?



## MDShunk (Jan 7, 2007)

I've never been able to wire an electric "on demand" water heater in a dwelling without a service upgrade. Gas only. There's no way in hell you'll wire an electric on demand water heater without a service upgrade.


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## BryanMD (Dec 31, 2007)

Florida? install a holding tank in the attic = solar/radiant


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## NolaTigaBait (Oct 19, 2008)

The last one i did was a 24kw unit. The load calc came out to around 215 amps. Yeah, the chances of it being on along with all other loads is slim, but you have to account for them. There is demand factors for dryers or ranges and the such, but I don't think the water heaters have such a thing.


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## randomkiller (Sep 28, 2007)

MDShunk said:


> I've never been able to wire an electric "on demand" water heater in a dwelling without a service upgrade. Gas only. There's no way in hell you'll wire an electric on demand water heater without a service upgrade.


I have found the same issue, gas is the way to go in this area when not looking to upgrade the service.


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## MDShunk (Jan 7, 2007)

All of the electric on demand water heater I've wired took a bunch of 30 amp circuits. I've never wired any that took 60's. The last one I did took 5, 30 amp circuits. That might have to do with what most local suppliers sell? I dunno. I vaguely remember some NEC requirement that water heaters be served with no greater than 30 amp circuits, but I'm not intrigued enough to look it up .


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## Bob Badger (Apr 19, 2009)

MDShunk said:


> All of the electric on demand water heater I've wired took a bunch of 30 amp circuits. I've never wired any that took 60's. The last one I did took 5, 30 amp circuits. That might have to do with what most local suppliers sell? I dunno. I vaguely remember some NEC requirement that water heaters be served with no greater than 30 amp circuits, but I'm not intrigued enough to look it up .


It's actually 60 amps as the limit but that OCP can be in the unit.

I have seen electric boilers for building heating supplied with 3 - 200 amp 480 volt 3 phase feeders.


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## MDShunk (Jan 7, 2007)

Bob Badger said:


> I have seen electric boilers for building heating supplied with 3 - 200 amp 480 volt 3 phase feeders.


Come to think of it, you must be right. I've actually wired oil-water separators (evaporators- essentially, big water heaters) that were similarly supplied, but had a row of breakers inside their control panel to each bank of Chromalox type elements.


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## robnj772 (Jan 15, 2008)

They have become real popular by me. Everyone wants one,no one wants to pay for it.
Alot of houses still don't have gas and don't really care because they are mostly summer homes.That being said since I am on the beach there are no basements and everything on the first floor must be above flood elevation .
On Demand heaters are a good way on saving space BUT when they get the price to upgrade the service they decide to just give up a closet somewhere.


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## william1978 (Sep 21, 2008)

They mainly use the gas one's around here.


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## Southeast Power (Jan 18, 2009)

I was in a supply house and saw a handyman type guy buying one. I asked him how much of a service upgrade he had to do for one of them and he looked at me like I was crazy. He says he puts them in all of the time in condos. With no service upgrade.
HOLY COW!! 
Can that many condos have FPE breakers?


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## Southeast Power (Jan 18, 2009)

MDShunk said:


> I've never been able to wire an electric "on demand" water heater in a dwelling without a service upgrade. Gas only. There's no way in hell you'll wire an electric on demand water heater without a service upgrade.


I cant wait to see what happens when they start charging residential customers demand rates


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## macmikeman (Jan 23, 2007)

The "experts" at HD sell them based on this: "Oh they have been very popular to use in Europe for decades now." 

The voltages supplied to dwellings over there are also twice as high as here, hence it is also 1/2 the demand on the system, so yea in Europe......


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## Frasbee (Apr 7, 2008)

Are those on-demand any more efficient, energy wise?


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## crazymurph (Aug 19, 2009)

I was just looking at the "on demand" water heaters on Home Depot's site. The model I saw needs 3 2 pole 40 amp circuits with #8 AWG minimum. At a price of $650.00 and all the expensive wiring needed, the payback time is an eternity. It was also recommended to be installed in a minimum 200 amp service. The other thing I noted was that it had a 105 degree hot water rating assuming a 60 degree inlet temperture. That would mean many people would need a tempering tank. The average homeowner would spend about $3000.00 or more for this high tech water heater that will be shot within 20 years.


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## Protech (Aug 6, 2009)

I see allot of home depot installers just slapping in whole house electric tankless heaters on a 100A service. You turn on a faucet and the voltage drop is so bad the lights ALL dim. Scary stuff.

Even on a 200A service you can see the lights dim.


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## egads (Sep 1, 2009)

A timer on a regular tank type is always a good idea. I wonder how many folks with electric water heaters in vacation homes forget to turn them off when leaving?


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## te12co2w (Jun 3, 2007)

Around here the plumber's just tell the homeowners that one of these electric jobs is just the ticket. They don't care if the service is big enough to handle it. They just put it in. Then the electrician gets the call to hook it up. Most of the ones we've done needed two 60amp circuits. One needed three 40amp if I remember correctly. The homeowner never wants to spring for a service upgrade. 
Our water is so cold that these electric heaters do not live up to the hype here. By the time they heat the water to proper temp, flow is usually so low that the homeowners don't like it. We have disconnected probably as many electric models as we have hooked up. Gas ones seem to do a lot better though.


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## George Stolz (Jan 22, 2009)

I would assume all electric IWH's dim all the lights in a home appreciably. Would that be a safe assumption?

I've only wired one gas one.


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## Greg (Aug 1, 2007)

At one point I looked into getting for my house and the literature stated that the dwelling needed at a 300A service. I was not going to go to that type of trouble for myself and I have a 200A service to begin with. Instead I drained and flushed my hot water heater until the water flowed cleared and replaced the elements and t-stats on the unit. The cost was about 30-40 bucks and a 12 pack of beer and my unit heats up a lot quicker now, so I don't waste as much water waiting on hot water.


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## Mountain Electrician (Jan 22, 2007)

I've wired one...(3) 40A circuits, did require a service upgrade...and yes, it did dim the lights..even when it was the only load turned on. I have a propane on-demand water heater. The lights don't dim when they come on. :thumbsup:


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## fraydo (Mar 30, 2009)

I looked into one when my old w/h gave out since i was in the market for a new one anyway. Three 40-A 2-poles and all I have is a 125-A service! Forget it. I just bought a regular one. As for the timer, I have always had one installed. It turns on in the morning 30 minutes before we wake up and shuts off 30 minutes after we leave. That and two hours in the evening is all I need in the house. If I had gas service I would consider it.


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## Protech (Aug 6, 2009)

If installed correctly, a modern electric heater losses very little heat. Installing a 24hour timer will do little or nothing in the way of energy savings. Now if they are gone for the weekend every weekend then I could see using a weekly timer.

Just to give you an idea of how long a heater can hold heat……I have repiped houses where the heater was off for 2 days and when the water was turned back on (but not the breaker) the water was still hot. It had only dropped a few degrees. This is only true for modern heaters with insulated pipes and heat traps. Older heaters will lose quite a bit of heat though due to poor insulation. 



egads said:


> A timer on a regular tank type is always a good idea. I wonder how many folks with electric water heaters in vacation homes forget to turn them off when leaving?


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## Toronto Sparky (Apr 12, 2009)

I have been told over and over again that the "On Demand" water heaters are ok for showers and baths , but not near hot enough for dish washers or even clothes washers (to a lesser degree)
Dish washers need to be up around 160-180 degrees to sanitize plus the detergent will not desolve at lower temps.


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## Toronto Sparky (Apr 12, 2009)

The timers on water heaters are for us folks that have "time of day" "smart meter" billing.


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## JohnJ0906 (Jan 22, 2007)

Mountain Electrician said:


> I've wired one...(3) 40A circuits, did require a service upgrade...and yes, it did dim the lights..even when it was the only load turned on.


I had the same experience.


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## Protech (Aug 6, 2009)

Yeah you can save a little by being on a "load shifted" billing setup with one.



Toronto Sparky said:


> The timers on water heaters are for us folks that have "time of day" "smart meter" billing.


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