wrote:
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.


Well Nick, since you encouraged me to "do the numbers", I just did.

We'll use your 6 times a day "waiting for hot water" figure.

Our city water (combined with a sewage charge that's more than the water
charge!) costs us very close to $5.00 per hundred cubic feet. I know
that's high, but we live in one of the 40 cities and towns that is still
paying for the cleanup of Boston Harbor, claimed to have been polluted
by over a hundred years of those 40 municipalities depositing their
sewage into it.

I just used a gallon milk jug to check what it took to "get hot water"
in the bathroom in our home furthest from the water heater. The jug was
nearly filled when the water got "as hot as she gets" and it took 25
seconds to get there. Normally, I'd find the water was warm enough to
start using in about half that time, but let's play it conservative.
BTW, no one had been there to run any water for at least six hours
before my great experiment.

That computes Captain, because that bathroom is maybe 50 linear feet
from the heater, and assuming maybe 30 feet of 3/4" pipe and 20 feet of
1/2" pipe worst case, there's about 0.8 gallons of water in the hot
water piping to sweep out, and the pipe itself needs to get heated in
the process.

So, if we "waste" that one gallon of water down the drain six times a
day, 365 days a year, the cost to do that, even at my outrageous water
rates, will be less than $15 per year. If you live where water costs
less than $5.00 per hundred cubic feet the cost will obviously be
proportionally lower.

That's gonna take a long time to pay off the purchase and installation
costs of an undersink unit. Say Nick, how many vanity cabinets have you
seen with a power outlets inside 'em? Have you priced what an
electrician would charge to install one there for you?

All the other factors cancel out, save for the cost of power to run the
circulating pump and the cost of the water you "waste" waiting to get a
glass of "cool" water to drink because warm water has just been pushed
into the cold line. Of course, there's also some additional savings from
decreased waiting times for hot water at other nearby faucets IF the
motion detectored pump had recently been activated.

The pump power cost, if it really only draws 25 watts, is negligible. I
figured it out to about half a kilowatt hour a year running for 30
seconds 6 times a day. That's nuttin' to worry about.

The "cold water waste" is a function of your thirst and taste of course,
but it's gotta take something away the water you save by not wasting
that water from the hot water faucet.

I suppose that if you're an impatient type and put a price on your
discretionary time then the total waiting time for the hot water to warm
up enough to use, which I make to be about 10 hours a year, would easily
swamp all the other cost calculations. But, I try hard not to think
about stuff like that while I'm waiting for traffic lights to change and
supermarket checkout lines to move.

I think I've about "saucered and blowed" this one, Nick. Do what you
want about it, Thank G-d it's a free country.

Cheers,

Jeff

--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

http://home.comcast.net/~jwisnia18/jeff/

"As long as there are final exams, there will be prayer in public
schools"