Jeff Wisnia wrote:

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

Good.

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

OK.

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 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...

At about 2 gpm? Not much...

that bathroom is maybe 50 linear feet from the heater, and assuming maybe
30 feet of 3/4" pipe and 20 feet of1/2" pipe worst case, there's about
0.8 gallons of water in the hot water piping to sweep out...

OK.

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.

....O.8x6x365 = 1752 gal or 219 ft^3/year, about $11. Heating it takes
1752x8(120-60) = 841K Btu or 247kWh/year, about $25 at 10 cents/kWh.

That's gonna take a long time to pay off the purchase and installation
costs of an undersink unit...

IMO, the question is" "If a body desired instant hot water,
which is cheaper, a) Grundfos, b) Taco, or c) Bosch?

Bosch may not be a good solution, with standing pilots or 5-10 sec delays.
Taco is a better solution than Grundfos, with temp sensing and a motion
detector vs a timer.

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 Grundfos pump on a timer with no temp sensing would run a lot more
than that. Running for a mere 2 hours per day, eg 8-9 AM and 9-10 PM,
it might use 50 Wh of electricity plus about 2 kWh for pipe heat losses,
totaling 2.05 kWh/day or 749 kWh/year, ie $75 at 10 cents/kWh. The Taco
system might run for 3 minutes per day, filling half the pipe (only the
hot pipe) at a cost of $36/year, about the same as the manual method,
ignoring trips to the loo or the kitchen without hot water use.

Nick