ECN Forum

Instant Under counter Hot Water Heaters

Posted By: Yoopersup

Instant Under counter Hot Water Heaters - 05/07/08 07:32 PM

Instant Hot water heater under the sink Bradford model EFT-28000-4-T-10 208 volt single phase. Draws close to 140 amps.
Theres 45 units that theses are POSSIBLY going to be installed. As far as I see it each one must be rated for condutious duty(X125%)45 x 6075x125% aprox 760 amps ???
Anyone know of any derateing ect in this case?? Seem like a lotta power for Hot water???
Yoopersup
Posted By: electure

Re: Instant Under counter Hot Water Heaters - 05/07/08 10:03 PM


Article 100 defines continuous load as:

"A load where the maximum current is expected to continue for 3 hours or more"

That's one heck of a long time to run the sink.
Posted By: Yoopersup

Re: Instant Under counter Hot Water Heaters - 05/07/08 11:23 PM

So Hot water Heaters don't need the 125 % either????
422.13 ?????? come into play
Posted By: electure

Re: Instant Under counter Hot Water Heaters - 05/08/08 12:14 AM

The water heater is not a storage type. It is an "On Demand" type.

It heats the water when needed, and only when needed.

Here's a PDF
If you scroll down to "Series Three" you'll find it there.
http://www.bradfordwhite.com/images/shared/pdfs/specsheets/217b.pdf
Posted By: Yoopersup

Re: Instant Under counter Hot Water Heaters - 05/08/08 01:01 AM

So where does it deal with Demand type in the NEC?? and whats to stop it from being on for three hrs or more????
(I knew it was demand type Thus the product #)
Posted By: sparkyinak

Re: Instant Under counter Hot Water Heaters - 05/08/08 01:04 AM

Insta hots are not considered as storage units per 422.13.
Posted By: renosteinke

Re: Instant Under counter Hot Water Heaters - 05/08/08 02:03 AM

Yooper, I might see a few errors in your thinking.

These are single-phase 'whole house' water heaters. I assume that means that these will each be going in a different residence, and different panels.

Does the load seem high? Sure - that's the price you pay for 'instant' heat.

When you do the load calcs for multiple dwellings, there's a multiplier for your "diversity factor." The effect of this is, whether you use the 125% figure or not in each individual panel, I don't think it will change the final total service needed.

Looks like you need 3 two-pole breakers - and they;ll need to be mounted next to each other, so they can be considered as disconnects 'grouped together.'
Posted By: Yoopersup

Re: Instant Under counter Hot Water Heaters - 05/08/08 11:36 PM

I called the Company your right, Three 2 pole 40 amp breakers for each unit . and thats the Minimin size they say would be required to feed a, Shower, Bathroom sink, Kitchen sink combo. Becta there not going in!!!.
Posted By: SteveFehr

Re: Instant Under counter Hot Water Heaters - 05/09/08 10:39 AM

It's insane how much power it takes to heat water on demand, isn't it? I would have had to upgrade my service to put in an in-use hot water heater for my home. Gas isn't much better- the size gas like you need for even a 1-shower-at-a-time tank line that is obscene, too.
Posted By: ghost307

Re: Instant Under counter Hot Water Heaters - 05/09/08 12:53 PM

It doesn't really take more energy to heat the water; it's just that you're trying to heat it in seconds instead of minutes. If you think about the gas versions, you're using 30 minutes worth of a gas flame in a few seconds. That means that the flame will look more like a welding torch than a stovetop burner.

My electric one takes (4) 30 Amp 240V circuits, but it doesn't really show up as a noticable amount on my bill; so I'm not using a LOT of energy, I'm just using the same amount very very quickly.
Posted By: renosteinke

Re: Instant Under counter Hot Water Heaters - 05/09/08 02:08 PM

I suppose we need to get ready to see more point-of-use heaters. The method does have it's advantages.

In "traditional" construction, all the things that used hot water were placed close to each other, and the heater was nearby as well. For example, in a recent building I worked on, the kitchen counter was on the opposite side of the bathroom wall, with the heater placed in the basement directly beneath.

Yet, today homes are not laid out that way. Bedrooms are scattered about, each with it's own bath. The kitchen is often pretty distant from the garage - a common place for the heater. Yesterday's job was in such a home, where the kitchen was the room farthest from the garage.

In such designs, the small size of these heaters, the easier piping, and the lack of delay waiting for the hot water to reach the faucet make them attractive options.

I would not be a bit surprised if someone starts selling "water heater cable" ... a relative of Romex, with 6-#8's and 3-#12's in it. That, naturally, will lead to countless discussions here about de-rating issues laugh
Posted By: sparkyinak

Re: Instant Under counter Hot Water Heaters - 05/09/08 02:21 PM

Fuel oil contain 138,000 btu's per gallon. One kilowatt of electricity contains just under 4000 btu's. My on demand oil fired waterheater burns just over a gallon an hour and 88% efficient so it utilizes about 122,000 btu's per gallon. Electric heat is 100% efficient so you need about 30kWh of power with an equivalent heating equipment.
Posted By: SteveFehr

Re: Instant Under counter Hot Water Heaters - 05/09/08 04:13 PM

Oh, believe me, I understand the physics involved. But the requirement remains to get those BTUs into the water as fast as it's used, which requires a fat pipe, beit electrical or gas.

Some energy savings are realized over a conventional hot water heater in that there is no thermal loss through the hot water tank insulation. In practice, though, I think these losses are overstated- yes, a hot water heater uses a lot of electricity, but that's because it's heating up a lot of water. I think I worked it out once to around 25-50 cents per shower. Of course, I was taking a shower at the time I worked it out, so those numbers might be a bit off wink
Posted By: EV607797

Re: Instant Under counter Hot Water Heaters - 05/09/08 08:55 PM

Romex with 6 #8's and 3 #12's............Now that's funny!
I can't even begin to fathom how much that would cost per foot, not to mention the weight!

Please forgive my ignorance here as I never did well in school with math. So if I understand:

(using local east coast prices)

30KW of electricity costs about $2.10 for an hour.
One gallon of fuel oil costs about $3.75 for that same hour.

The net BTUs produced are roughly the same. I know that oil and gas prices are insane right now, but with nearly a 80% difference, why would there even be an option here?
Posted By: Tesla

Re: Instant Under counter Hot Water Heaters - 05/10/08 04:26 PM

The story is the waste of energy while the hot water is maintained 'at idle'.

Plainly, energy is lost every moment of the day from the hot water system. That's no problem if you're on solar power. Otherwise, the bulk of your energy consumption tends to be for the heat lost while NO WATER IS FLOWING. Tankless gains its merit from that fact.

If three phase power were available, then a single three pole C/B at 208Y120 could power up the three elements when wired delta.

Aiming at the residential market this high power insta-hot stacks three single phase 240V elements into one device.

I pity the poor installer who has to get (6) #8 conductors through a 3/4" KO. My advice: open it up to 1".

As for getting the field wiring in place start thinking of 1" PVC in the underslab/ or 3/4" ENT/SMURF tube (Flex?) with pre-installed conductors in the overhead.

Either way, quite a bump up in effort for the electrician.


Posted By: walrus

Re: Instant Under counter Hot Water Heaters - 05/10/08 11:42 PM

heat pump hot water heater
http://www.nyletherm.com/waterheating.htm
Posted By: Trumpy

Re: Instant Under counter Hot Water Heaters - 05/11/08 12:38 AM

Originally Posted by renosteinke
I suppose we need to get ready to see more point-of-use heaters. The method does have it's advantages.

In "traditional" construction, all the things that used hot water were placed close to each other, and the heater was nearby as well. For example, in a recent building I worked on, the kitchen counter was on the opposite side of the bathroom wall, with the heater placed in the basement directly beneath.

Yet, today homes are not laid out that way. Bedrooms are scattered about, each with it's own bath. The kitchen is often pretty distant from the garage - a common place for the heater. Yesterday's job was in such a home, where the kitchen was the room farthest from the garage.

John,
Do houses in the US no longer have a Laundry room?
Over here, this room is often the most central room of the house (in a single level construction).
Often the hot water cylinder would be installed in there with lagged pipes run to the various plumbing appliances.
I have also seen them installed in roof spaces, but that's a whole thread in itself.
Posted By: renosteinke

Re: Instant Under counter Hot Water Heaters - 05/11/08 02:01 AM

Yes, we still have "laundry rooms." though 'out west' there is a tendency to place the laundry equipment in the garage.

The challenge is that we no longer have any location "central" to the water use, and the distances the pipes run has grown quite a bit over the years.

For example, yesterday's job was a house whose floor plan sort of resembled the letter "F." Bedrooms were in the base of the "F," and the top left part. The kitchen was the top right. The garage the middle "bar." It's almost as if they wanted things to be as far apart as possible.

Another common design these days is the "O", or courtyard design. In this arrangement, one side is a massive garage (imagine it at 6:00) most bedrooms would be at 11:00, with a guest suite at 3:00, and the kitchen/ laundry at 7:00.

Kind of makes you miss the traditional ranch style home.
Posted By: EV607797

Re: Instant Under counter Hot Water Heaters - 05/11/08 04:48 AM

Sounds like as much of a horror show for electricians as it is obviously for the plumbers. That makes our traditional colonial construction around here with basements sound a lot better than I thought. We don't have any equipment in garages here, but then again, we have basements for the HWH, HVAC and laundry facilities. I will admit that my laundry room is on the second floor which is a lot more handy.
Posted By: gfretwell

Re: Instant Under counter Hot Water Heaters - 05/11/08 08:50 AM

Basements are called "indoor swimming pools" in Florida and second stories tend to be called "wind borne debris". Long, low ranchers are the norm. (although we do see piling houses at the beach and some 2 story McMansions) The architects usually put the laundry on the opposite end of the house from the master bedroom so you have a lot of pipe between them.
I do think that if you just had 20-30 gallons of storage in the attic you would have all the hot water you need most of the year here for free.
Posted By: Sixer

Re: Instant Under counter Hot Water Heaters - 05/11/08 02:00 PM

A lot of new homes here have electric heat because they're outside of city limits and there is no natural gas available. Those that want to add an electric on demand hot water system usually back off when we tell them that a 200 amp service won't be enough. At just over 7¢ a kWh, the payback period in energy savings could take decades to cover the additional cost for a 300 or 400 amp service.
Posted By: gfretwell

Re: Instant Under counter Hot Water Heaters - 05/11/08 03:11 PM

If you are using electric heat there is no wasted energy from a regular water heater. It is still heating your house. Add a recovery unit on the A/C and you are getting free hot water in the summer(minus the recycled heat into the space from the tank)
Posted By: renosteinke

Re: Instant Under counter Hot Water Heaters - 05/11/08 03:52 PM

Another factor in the equation is .... increased prosperity.
Where there was once but a single master bath, now homes often have several baths. As are the larger jacuzzi tubs. There are more appliances - like dishwashers - and they're larger. Finally, folks don't want to wait for that hot water to arrive.

So, the old way - having a single big tank of hot water - is looking inefficient. Having multiple heaters, located much closer to the user, starts looking attractive. Even though the new homes are simply massive - the last one I did was 14 times larger than my home - folks also like the compact size of these instant heaters.

Here's one way to look at things .... imagine taking an extension cord into a home, and using a generator set just outside a door. In my place, a 25 ft. cord would let you reach nearly everywhere. In these newer homes, a 100 ft. cord would be needed.
Posted By: sparkyinak

Re: Instant Under counter Hot Water Heaters - 05/11/08 04:27 PM

With more and more items be electrified, I do not see that multiple insti-hot water heaters being viable. Even on a 200 amp service. The one on the tub alone will likel be 100 amps for the large amount of hot that does not leave much for the rest of the house. The HO will not hesitate to use hot water while some one is in the shower and boom, out goes the lights.
Posted By: renosteinke

Re: Instant Under counter Hot Water Heaters - 05/11/08 07:05 PM

Load calculations are one of the things that separates real electricians from the pretenders laugh
Posted By: Sixer

Re: Instant Under counter Hot Water Heaters - 05/11/08 09:06 PM

We ran into this recently. Home totally renovated, 200 amp service already existing. Customer wants electric heat (not central) and he had already bought an on-demand water system. The hot water alone was 24kw (100 amps @ 240 volts)and because the hot water had to be calculated at 100% demand, that left us with 100 amps for the rest of the calculated load. We reduced the total heating to 7kw - not enough (in my opinion) for a 2-storey (600 ft² per floor)with a full basement which also needs to be heated.

Owner is convinced that the on demand system will save him money and that the electric heating for the house will be adequate. We also tested the on demand system and at full volume, it heated the water to luke warm from 36ºF. Owner had to cut back the input valve in order to get the output temperature to an acceptable level. There's no way this tankless heater will be able to keep up with a shower, dishwasher and washing machine at the same time, and space heating had to be sacrificed to boot.

This tankless heater needed a feed of #2 copper (125 amp breaker), which cost the homeowner over $500 for the wire alone (and wire prices have gone up since then) because the tank was closer to the bathroom and kitchen and quite a ways from the panel. This is something else to consider when calculating the payback period.

If a customer wants a tankless system I will recommend a gas unit, not electric. But not everyone has that option when gas isn't available.
Posted By: walrus

Re: Instant Under counter Hot Water Heaters - 05/12/08 10:36 AM

They make propane fired on demand gas hot water heaters.
Posted By: SteveFehr

Re: Instant Under counter Hot Water Heaters - 05/12/08 10:53 AM

Originally Posted by walrus
I was just about to ask why we don't see anything like that on the market! Carnot heat pumps are about 2-3x more efficient than a straight resistance element. And it would essentially do cogen (AC) in the summer, too. The unit in that photo looks far too small to be effective, though. My guess is that the average household simply doesn't use enough hot water to justify the cost.

As for the condensate pump option... water tanks are all required to have catch pans and drains, and they're ALL properly maintained, right??
Posted By: walrus

Re: Instant Under counter Hot Water Heaters - 05/12/08 11:07 PM

I actually have one. Works great, never pay for itself:) but it does dehumidify my walk out basement and I'm ducting it into my living room for the AC. I can't run it all year as I'm in Maine and it would freeze my basement solid in the winter:) Why folks down south aren't using them is baffling. less baffling than folks down south not using solar though, that drives me crazy
BTW it has a COP of 2.5 and cost me 800 bucks
Posted By: gfretwell

Re: Instant Under counter Hot Water Heaters - 05/13/08 02:03 AM

The thing they sell a lot of here is the heat recovery unit on the A/C. That is pretty much free hot water. I still think a 30 gallon tank in the attic would just stay hot enough for most people's needs 6 months of the year.
© 2019 ECN Electrical Forums