What parameters was that based on? Like RBM said,
I think those are just nuts. First, if you're comparing
using a push button type pump with no pump at all,
the savings in gas is minimal.
With no pump, you have to heat enough incoming cold
water to replace the water that is in the hot water pipe
between the water heater and the point of use. That's
not a lot of water.
With a pump, you have to heat enough returned water
to replace the water that is in the hot water pipe.
So, the difference is in heating a gallon or two of water
either from about 45F or about 65F. The other small
savings would be in the cost of the gallon or two of
water that goes down the drain.
My whole gas bill in summer, which is just for
the water heater, is only $17 or so.
If you're comparing a push button system to one that
already has a pump and keeps it circulating 24/7,
then it would be more substantial, but still, those
numbers are hard to believe.
The biggest drawback to these systems, which I bet
TOH never mentioned, is that unless you install a
seperate return line from the points of use back to
the water heater, the stale, tepid water is going back
into the cold water line. There it will be available for
anyone who draws a glass of what they think is cold
fresh water. That person could be at the point-of-use
where the pump is or anywhere else along the path
of the cold water pipe going back to the water heater.
Meaning if you're drawing a pitcher of water to mix
the kids some Koolaide in the kitchen, you could be
in for a surprise. Before installing one, I'd analyze
what else is on the cold water line and figure out
hot to install a new line if necessary,.
In addition. no one (including ATOH) ever mentions the cost of running
power for the pump.
On the ATOH episode in question, there was clearly a brand new
receptacle shown inside the vanity where the pump was placed.
Depending on the current electrical situation and homeowner's skill
level, the installation of the receptacle could add significant cost
(percentage wise and payback wise) to the installation.
That's a good point. I guess in some cases you could
manage to get the pump cord to a nearby outlet without
it looking like hell. But as you say, in the ones I've seen
installed, they always seem to have that receptacle right
there in the vanity. Another problem could be if you don't
have a vanity, ie pedestal sinks.
I was going to mention pedestal sinks (since I have one) but I chose
That adds another level of complexity since you now need to figure out
where to put the pump (in a closet? in the basement?) and then figure
out how to plumb it so that it turns off when hot water is at the sink
(not just at the pump) and run the wires for the push button or hope
the remote (Honey, where is the remote for the sink?) can turn it on
My apologies.... I don't believe their "savings numbers" either.
I was just throwing out some general concepts about where the savings
would come from.
I think they might have been double dipping on their energy savings.
Looks like no one visited
the author did a decent energy analysis
24/7 small recirc pump ~ 500 to 1000 kwh per year
~200 gallons of propane per year (about 256 therms equivalent)
About a 1/3 of this waste can be eliminated by using a timer, more by
having some sort of temp sensor.
Even more by doing the push button thing.
A lot of work & expense to have "instant water".
The "best" solution is thermo-syphon with well insulated hot water
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