krypto

Most all residences in my state have 150 or 200 amp services (some condos, and older homes can be 100 or 125 amp) Here's my question, if the service was calculated with a standard 4500 watt water heater, how can an 18000 watt 240 volt (75 amp) or larger "on demand" water heater possibly fit on this service without a service upgrade? Is there a demand factor on these units that I might be missing? When I called the manufacturers of these units, they all say that it is possible that all elements can be on at the same time, if the demand for hot water is high, such as several baths and sinks going at once. What am I missing that allows these to be put into existing residences, running from (2) to (3) 60 amp circuits??

MDShunk

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

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

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NolaTigaBait

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.

randomkiller

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

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

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

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

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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Yep...

william1978

They mainly use the gas one's around here.

jrannis

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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jrannis

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

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macmikeman

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......

Frasbee

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

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crazymurph

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.

Protech

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.

egads

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?

te12co2w

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.

George Stolz

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

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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