Jeff Wisnia wrote:

...if you have to have this, I'd add a tankless unit in the bathroom.

I don't have to or want to, but if I did, I'd want a lower-energy solution.

They cost a lot and keep a small amount of water hot all the time.
You might compare the capital and energy costs of the tankless and
Taco solutions, with a motion detector that moves hot water for 30
seconds, using actual numbers.

Yes, but if it's in a john, howya gonna keep that motion detector from
causing it to waste energy for 30 seconds every time you go in the to
take a leak?

You aren't, and the pump would only run long enough to warm the pipe
to the distant fixture, which might be less than 30 seconds. I suggest
you compare that energy to the standby energy used by a typical tankless,
over a day, using actual numbers. This might require an actual phone call
to an actual tankless manufacturer. It's my impression that most tankless
heaters keep a small volume of water hot 100% of the time, so the standby
loss is not zero, and it may be more than the energy lost by pumping a
half-gallon of hot water 6X(?) per day.

Well, you are wrong about that Nick, or Bosch is guilty of saying what
the native americans used to call, "that which is not so".

Maybe the latter. I see a number of Bosch units have standing pilots.

Take the "Interactive tour" and you'll see that they confirm there's NO
standby energy use.

That's what they say...

http://www.globecomsoftware.com/vend...ess/index.html

They use FLOW to trigger the heating, so, except for the little bit of
heated water left in the coils when you close the faucet, there's
minimal "standby losses".

There's one loss. The Bosch distributor CEC also mentioned a "5 to 10
second delay" between the start of water flow and actual hot water in
the HX water ignition system.

The closest thing I found to a zero-standby-loss instant heater was
the $200 Powerstream RP12T... 240 V at 50 amps to heat 1.5 gpm "in
a cold climate." But that seemed to have other problems, eg poor temp
control with varying pressure, eg in a house with a well vs city water.

That probably would tip it in favor of the cheapo "jam it down the cold
pipe" designs from an overall cost perspective, but that wasn't my
original point. I was saying that I think those cheap systems are a
stupid way to solve what isn't a very big problem anyway. And, that if
you want to do it "right" then a separate return pipe with insulation or
a tankless heater is the proper engineering solution.

In my opinion, that's "not proven," and likely untrue.

Nice meeting you,

Likewise.

Nick (ex K3VZW, BSEE '68, MSEE '87)