tankless electric water heater [RE-wrenches]

Bill Loesch, Saint Louis Solar bill_loesch at compuserve.com
Tue Jun 7 05:50:04 PDT 2005


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Message text written by INTERNET:RE-wrenches at topica.com (Kurt Albershardt)
>
Thanks for all the responses, guys.




--On Tuesday, May 31, 2005 12:34 PM -0400 "Bill Loesch, Saint Louis Solar"
<bill_loesch at compuserve.com> wrote:
>
> There are two major distinctions between all tankless electric
> manufacturers (and there are a _lot_ more elec tankless than gas
tankless):
>
> Some of the manufacturers (like Eemax) use a bare wire immersed in the
> water flow to directly heat the water.
>
> Others (Redring, Stiebel Eltron) use a heating wire covered by a copper
> jacket.
>
> Probably not a lot of difference between the two techniques unless water
> scale becomes an issue. The bare wire sheds the scale much better than
the
> jacketed wire.


Do you happen to know which category the Bosch units fall into?

Kurt, I am unaware of any Bosch manufactured electric tankless imported
into this country. Controlled Energy Corporation (CEC) was the exclusive US
importer of Bosch gas tankless until earlier this year when they were taken
over by Bosch. Over the past few years CEC has sold both the EEMax whole
house units and the Redring whole house electric tankless heaters under
their own label of PowerStar. The current offering from Bosch (nee CEC) is
the Redring model which uses the copper jacketed heating wire technique. As
of this date a failure of any of the 6 heating elements (in the 120 Amp
model) 4 heating elements (in the 80 Amp model) would require a changeout
of the entire box (which is one very good reason to put proper unions on
the installlation). The Redring does offer an external adjustment for
temperature control (a nice feature if you are operating in a climate where
the ground water temperature will change markedly between the summer and
winter).

The EEMax whole house electric tankless heater uses the bare wire immersed
in the water (better water scale resistance) and additionally uses only one
independently replaceable heating element for each two circuit 40 Amp leg.
My experience is that EEMax has always provided these replacement elements
at no cost. Their design also provides a temperature adjustment; however
you must take off the cover to get to it. I have not recommended to any of
my customers to do this as if they don't shut off power to the unit they
can create a lot of smoke and sparks by shorting the case to the heating
elements.

One of the best features of any well designed tankless heater (gas or
electric) is the potential to create the hot water at the temperature you
use it. Simply stated - if you want hot water turn on _only_ the hot water
tap - no need to blend cold water with the hot water. This becomes
especially important if there are single handle faucets in the house
plumbing. Especially older (worn) single handle faucets (or some newer
temperature and pressure balancing valves) where the cartridge or module or
??? may be worn or doesn't incorporate checkvalves into the design) and
allows bleeding of the cold water pressure into the tankless hot water.  


> Kurt, you have not identified what you want to do with the water (sink,
> shower, washing machine, etc. which will determine flow rate) nor have
you
> identified what the temperature rise you need for your climate. Both
> important considerations if you want to have satisfied hot water users
when
> winter comes with a potential for much colder inlet water than sumertime
> inlet water temperatures.
>
> If you have limited electric capacity, the only real variable you have is
> flow reduction to give the heater the time necessary to heat during the
> colder winter months. I'm told that 1.3GPM showers exist, I have not yet
> experienced them.


This will need to handle a shower and a sink for a bathroom.

Again with the limitation of the "two element" heater (two dedicated two
circuit 40 Amp breakers, 80 Amps total, 17.25kWatt) will be hard pressed to
deliver a 2 GPM in winter in Reno. Naturally, another "load" operating
simultaneously decreases the temperature rise to both users. I would
recommend sequential uses rather than simultaneous uses, especially in
winter.



> Any room for a temperating tank ahead of the tankless? Solar assisted
> temperating tank?


It's one of about 105 bathrooms in the building, which is being renovated. 
When it's complete, the south facing wall of the tower will be covered with
hot water collectors and there will be two 1500-gallon storage tanks in the
basement (one for DHW and one for radiant floor heat.)  Right now we just
need to provide for the caretaker and an occasional guest.




<

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