Looks like the way this one works, when the timer is sets the unit to
'on', the motor always runs and creates a pressure differential
between the hot line and the cold line (it pressurizes the hot line
relative to the cold line).
Then, the sensor-bypass thing is a thermostatic valve that just lets
water pass from hot to cold as long as the 'hot' side is below some
Neat! Wastes some energy in the pump, and having the hot line always
'hot' wastes some energy too.That's arguable if the pipe is in a space
you'd like to heat, since the wasted heat will just go into a space
you're trying to heat anyway.
It looks like as long as you have only one hot water heater, you only
need one pump, and can add the bypass valve to multiple faucets. If
your hot line from the heater branches, you put the pump before the
branch, and then install a bypass valve at the end of each branch.
If I was going to build something, I'd prefer the pump that sits at
the end of the line, and only activates when you push a button. The
pump runs until 'hot' water shows up. Hit the button on your way in,
when you're ready to wash up, the water's warm. If you're heading in
to just use the hot water, you still have to wait though...
Anyway, the pump you linked to looks like serious overkill- you want
something that can tolerate no flow ( a blocked pipe).
The way I understand it to work is that it turns the pump "ON" when
the low temp sensor detects 85deg. The pump sucks cool/cold water from
the hot line and pushes it into the cold line which in turn goes back
into the heater, closed system. When the "OFF" sensor detects 95deg it
turns the pump off.
I believe the timer is to stop circulating during un-needed times like
between 11:30pm and 5:00am.
The way my system is here I would need two pumps or another 200 feet
of pipes for the second sensor with that commercial system. I'd also
have top lag all those pipes. Tooooo hard.
Why not just let the water run until it gets hot? Should take no more
than a gallon and costs zero to set up and wastes no energy until you
need it ;)
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
** Posted from
The systems that I have seen depend on natural convection. The main hot water
pipe is ran under the floor, and a smaller return pipe is ran along the ceiling.
Any of these systems are huge energy wasters.
That's why I favor the one that pumps the cold water from the hot line
into the cold line only when you push the button. The 'hot' line
doesn't stay hot when you don't use any hot water.
It wastes a small amount less energy than just running the water
because the 'cold' water you're pumping into the water heater is
(probably) warmer than water drawn fresh from the mains, or from the
Thanks for th thoughts...
Dave, that is no different to running the tap other than it will
happen faster. I would still be putting a slug of hot water between
the water heater and the tap. The only thing is I would not be wasting
the water and that is not a huge concern with a well.
Looks like back to plan A, run the tap.
I recall a demand based pump from 20 years or so ago. It was
attached between the hot & cold lines at the farthest point of use
from the water heater. When a sensor detected a drop in the hot
line pressure the pump would turn on and pump from the hot line
into the cold line until another sensor detected that the hot line temp
was up to some setpoint. The thing was fully automatic, no timers, no
manual switches, and would trigger if any hot faucet was momentarily
I can't remember the name or manufacturer. Googling is left as an
exercise for the OP.
"Dave, I can't do that" wrote >
You're probably right about the timer costing less. But the sensor
couldn't be a flow switch as it was installed at the furthest point from
the water heater and the spigots closer to the heater couldn't trigger
it. I'm pretty sure it has to be a pressure sensor that could detect a
momentary drop in pressure. I do remember that it only took a
momentary on-off of any hot spigot to trigger the pump to turn on.
"Dave, I can't do that" wrote ...
If this was my house with a long-pipe problem, the timer would be a
15-minute wind-up Intermatic. You wake up and start your morning
ritual and allow 5 minutes for the pump to get the hot water to the
far end (without wasting any water down the drain) and then hop in the
nice hot shower.
If you keep the hot water pipes hot all the time with a circulating
pump at the far end, you waste a lot of the energy savings of an
instant water heater - as in, the system isn't supposed to be heating
the water /at all/ except when it is actually being used. Might as
well go back to an old style storage tank heater.
We split the house in two a long time ago, so there's no longer one
big electric water heater (and to raise the stupidity level it was in
the attic...) but two medium sized gas water heaters, one at each end
with fairly short runs.
One has 1 and 1/2 baths, the other has one bath, laundry, laundry
sink, dishwasher and kitchen sink.
First one that dies gets replaced with an instant - the kitchen and
laundry end gets the "large" unit, the 1 and 1/2 bath end can get a
"small". And during the process we can use the shower that still has
hot water, so it doesn't have to be done /right that moment/.