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did a online calculator, and came back with 126 amps for sub-panel? I would like the new sub to carry gen circuits and new bath in remodeled bedroom, and possible gen load for new 12 x 22 addition later for master bedroom, exist house is 1096', watts on name plate of w/h say 26850w at 240v, the kitchen is already on a seperate sub and on new 200amp service, do I really need 111 amps for this heater or am I missing some derating? done the calculator twice?chris
I doubt you missed anything. Instant hot water is "demanding".
I agree with Greg.
It's just a bit more than 111 Amps at 240V.

The reason that the instantaneous water heater does what it does is because it throws enough energy into the water to heat it up as it's passing through the unit, whereas the 'regular' water heaters take anything up to an hour to slowly heat the water up.

I don't find them to take any more energy in the long run, but MAN do they want a lot of it all at once!
I wonder if the sales people even hint to the homeowner that they may need to upsize their service when they are giving their sales pitch for these electric on demand water heaters.

Other than subdividing the heating element load as required in 422.11[F], how does the NEC handle these non-storage type water heaters?
Are they still considered to be a continuous load with the branch circuit and OCP sized at 125%?

The unit is supposed to require two 2-pole 40amp circuits, I believe at 240v, I have not personally seen name plate or booklet, but was assuming we could run new light/plugs and heat from sub-panel on opposite side of heater wall, and pull the old (closet)fuse panel into it and catch new later additional floor space, so I think the sub has to bump up to 150a instead of a small 12/24 125a, he originally purchased a QO 100a surface panel, and homeline 40amp breakers back in 2005 when he took out the original permit, this new sub is going to be in a bedroom wall. so I didnt want it to be massive... thanks for all your help. chris
Some of them require THREE 40amp 240 volt circuits.
My instantaneous water heater included the upgrade from 100A to 200A panel when I ordered the house. The saleman said that I was the very first customer who didn't question why the electric panel would be affected.
I have (4) 30A-240V branches feeding mine.
smile

BTW, I believe that the requirement for calculating water heaters as continuous loads is only for storage-type water heaters.
I know that instantaneous water heaters are supposed to save energy.

The advertising says so.

The idea is that most of the energy used by conventional hot water systems is lost to storage radiation -- not withstanding any insulation.

I've never seen a bathroom rated instantaneous heater with less than (3) 40A double-pole 240V breakers.

In commercial settings, they have totally taken over: just a bathroom sink fed at 30A at 208V, 240V or 277V.

Heat pump driven hot water would seem to be a winner -- but I've only seen it done in Hawaii.

It should be as common as dust in Las Vegas!
Yeah I just got word the one he's got is a AE125(bosch,cec?)needs 3 40amp 2pole bkrs. he found out when he bought it, that he should get a 200 amp main to replace his existing, Fire-Producing-Equipment service, did that in january after his main breaker burnt through the buss board. luckily it only burnt thru 3/4 of the siding and didnt enter the cavity, and that it was misting at the time....so if its not continously rated will a 125amp panel be ok? or bump up to 150a, or just run three circuits back to the new main(bad crawl, but not impossible) the calculator I used gave me 126amps required.
I think the problem with a heat pump water heater is initial cost and life expectancy.
In Vegas I would think they would use solar or just heat exchanging the HVAC condenser. A casino A/C condenser should be able to supply all the hot water they need most of the year.
The main heat losses in DHW are always, [no matter what system you select], in that little piece of pipe between the heater and the faucet. Every time you draw hot water, that length cannot be used and the heat is lost...
A conventional modern foam lagged storage cylinder, properly sized for family needs, has very low heat losses because the surface area is low compared to the volume stored. Surely the additional costs of new panels and wiring able to carry over 120 Amps will never get recouped?
Has anyone seen geothermal H/C equipment yet?
The main advantage of tankless water heaters is the fact that you cannot run out of hot water, no matter how many people shower.
In Europe this is even worse, since our typical tanks have reheating times of up to 4 hours. Typical tanks around here (for a single family home) are 150l (roughly 40gal.) and either 1500W 230V or 6kW 400V (3 elements). In Germany electric tankless heaters are fairly common, usually being 35A 3ph 230/400V. In Austria they aren't, because all our power companies will flat out refuse to connect such large residential loads (if the #@*$ thing alone draws more current than your service supplies you can't just connect it without asking).
These days with the low flow shower heads, it is pretty hard to run out of hot water. I am starting with 80F "cold water" anyway most of the year. I put a small water heater in the attic to get hot water into the far bathroom and kitchen a little faster. In the summer the element seldom comes on.
Ok so i got a sub-panel for disconnecting means, debating wiring with 1/0 aluminum romex rated at 120amps re 75 degree 310.16 (customer also bought that 5 years ago for different part of house he's no longer improving, I have experience terminating alum. but no real expans./contraction evidence heating at top end most subs are only loaded about 1/2 load, in my experience. otherwise #4 copper,
Alright chris, stop and slow down, sometimes I look at my posts and think how can anyone decipher what I'm trying to say......my concern is will aluminum feeders at near top of its load capacity expand and contract too much to be safe? I've only heard that some people don't use it as a rule.....or is there enough cushion in the tables to allow for that of course proper torque and no=alox being used. or is the load too high for aluminum?
I assume you must take this considering the source but the Alcan guy says aluminum wire performs better in the typical aluminum lug than copper.
If you properly torque the lug and use the goo I wouldn't worry about it.
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