Terry wrote:

Thanks for your "consumer review", I found it interesting. It's the
first detailed discussion of some of the "side effects" of tankless
water heaters that I have seen.

You say the output is limited to maintaint temperature. Are you able
to take a shower and run the dishwasher and run the washing machine
all at the same time, or does this result in inadequte flow at the
shower?

I don't know. Typically, we wash everything in cold water, so it's rare
that the washing machine would need the hot. The dishwasher, also, is
plumbed to the cold water line, and heats it own water; it's got a heating
element in the bottom (I think all dishwashers are like that).

Alright, I'll go check it. Turning on 2 showers, 1 washing machine (hot), 1
kitchen faucet (hot), 1 bathroom faucet (hot), and dishwasher (I don't
think it'll make a difference, but you asked...). Yes, the flow in the
showers is weakened. But it's still usable, and most importantly, it's
still HOT! OK, now turning on the fill faucet in the jacuzzi tub. (at
full flow, that faucet moves about 13-15 gpm--10 or so showers.) Now,
there's almost NO hot water on the upper floor, and the ground floor is
weak, too. And what's there is still at the correct temperature.


If you set the control point temperature for what you like in the
shower, doesn't this make the water too cold for the washing machine
and dishwasher?
See above washing machine & dishwasher. You can best answer that
question by filling in "what you like", "what temp you want in the w.
mach", and "what temp you want in the dishwahser". But check your
dishwasher first before worrying about it; it may not even be connected to
the hot supply.


How do you descale it?

Short answers (2):
1. Don't. Instead, get a decent water softener and feed the heater good
water.
2. Google for "descaling kit". Follow nose.

Long answer (hey, I warned you):

About water heaters and how they handle scale:
Note that tanked and tankless water heaters both produce scale, and both can
be descaled by pretty much the same process. In a tanked heater, it's not
that noticeable until the heater is FUBAR. Also, newer tanked heaters try
to cause the water flow to flush out the scale before the heater turns into
a block of limestone. Tankless heaters do this because of their
fundamental design (high velocity water flow).

My experiences:
What follows is my experience, along with some guesses as to why and how
these things happen. I'll try to make it clear when I'm speculating and
when I'm reporting what I actually saw.

Three types of water:
You get scale from stuff already in your water:
My wife and I lived in an RV (I'm a consulting Engineer; travel a lot), and
saw two kinds of water go through our RV-500: In Michigan, we saw
orange/red stain everywhere the water touched, and black scale from the hot
water system. Super Iron-Out cleaned up the stain. Conclusion: Iron-rich
water. In Ohio, the scale was white and crusty. Fizzed when mixed with
vinegar. I'm thinking calcium in the water.

Scale is not magically created; it comes from your water. So, if your water
doesn't have dissolved solids in it you won't get any scale.
My wife and I now live in a house (much gratitude to her infinite patience
putting up with living in a RV for 3 years!!). We got an appropriate water
softener for our well supply and we have no scale.

How the scale appears:
Water heater scale is produced when dissolved solids precipitate as the
water is heated. Talk to a chemist or industrial pipefitter (not plumber)
if you want more detail. With a tankless heater, the water flushes *most*
of the scale right out with the hot water. "Scaleless" tanked heaters do
the same thing by designing high-velocity water flow in the places where
scale is likely to accumulate. So, the scale come out of the heater along
with the hot water. And then promptly clogs up every &^%^$##!! screen in
your water system. Typically there are screens in the water feeds to your
washing machine, shower hot water, and sink sprayer. Well, that's where
the grit wound up in our RV.

Avoiding the problem altogether:
I'll say this again, even though it's implied above.
The best solution is to get a good water softener from Home
Depot/Lowes/Sears, etc. That's what my wife and I did in our house. It
works great, and we have not had a single speck of scale. Also, our
showers & bathtubs are clean and shiny, and we don't have to use Comet on
them. When shopping for a softener, I do NOT suggest you consult one of
the hard-sell triple-overpriced used-car salesmen that work for a company
whose name begins with "C"!!
You will NOT need to deal with the scale if you never get any.

Dealing with suspended scale in the hot water lines:
Use a filter. You'll be glad you did. (Remember those screens? It's a lot
easier to clean out ONE filter than a dozen screens. Which are buried in
your appliances) In our RV, I installed an ordinary water filter & used
spun yarn filter cartridges. Every month or so, I'd replace the filter and
pour out the quarter pound of "sand" that accumulated in the housing. If
you want a proper filter, you can get a hot-water rated one from
McMaster-Carr.

Descaling the heater:

Well, you can look up instructions on the internet, but here's what I did to
descale my RV500. I have never had to descale the 250SX.
As the scale forms, some of it will stick to the hot surfaces of the heater,
and it will build up. To descale the heater, first shut off the gas and
power. Then disconnect the heater from the water system and connect hoses
to the inlet and outlet. If you plan on doing this, put in the appropriate
valves during installation. You'll be glad you did! Next, you mix up the
appropriate concentration of acid (I used 10% sulfamic acid by weight.
That's ~1/2 5-gal bucket of water + 2 lbs of sulfamic acid). Use hot water
and dissolve it all. Stick the pump and the other hose into a second
bucket. Use ty-wraps to secure the hoses to the bucket handle so they
don't fall out! Pour the acid solution into the bucket. Plug in the pump.
Acid now flows round and round, and the solution in the bucket fizzes like
crazy. (That's why you only make HALF a bucket of solution!). After a
while, the fizzing peters out. When there's no more fizzy bubbles coming
back from the return hose, the reaction has stopped. At this point, you
have either run out of acid or you have run out of scale. Throw some
baking soda into the bucket. If it fizzes, you have run out of scale.
Otherwise you have run out of acid. If you're not out of scale, mix up
another batch of acid and do it again. When the scale is all gone, connect
up the heater again, and flush the remaining acid out of the lines by
opening up the hot water faucet nearest the heater.

Dealing with scale is a major PITA. Most people don't do it at all, and
just throw out their water heater when it gets ruined. The best solution
is to get your water analyzed and install the appropriate softener or iron
remover.


Finally, do you (or anyone) know if they make these things in electric
versions with reasonable capacity for a whole house? We live where
there is no gas avaialable, and electricity is cheap (so we heat with
all electric -- heat pump and electric backup furnace). We would need
an electric version of the tankless water heater.

Yeah, you can get electric ones, too. I think CEC sells them. The 250FX
outputs (at most) 142,968 Btu/h (41.8 kW). Efficiency is 86.5%, making
maximum input 175,000 Btu/h (51.2kW). For electric with the same
efficiency and output you'd need a little over 230A(RMS) at 220V(RMS).


Thanks,

Terry