True or False?
A hot water recirculating pump won't decrease the amount of time it
takes to get hot water to a fixture, it will only eliminate the waste
caused by the water running down the drain.
(Another Ask This Old House inspired question)
a. runs all the time or
b. is a passive gravity system
the whole idea of the passive system which will work in any house with a
water heater below the level the fixtures are on, is INSTANT hot water.
We had it introduced to us in 1970 when my parents built on to their
house. It worked (and still works) great!
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But these waste a lot of heat because they are continuously
circulating. We have a second home in Fl and the water heater is at
one end of the house and 3 bathrooms at the other. it can be a pretty
good wait for the hot water to come up so I installed one that you hit
a switch to call up the hot water. I mounted the switch by the the
light switch in the bedroom figuring this would give the pump a bit of
a head start before you made it to the bathroom.
the 'waste' is minimal during cooling season. and zero during heating
season. It's about instant hot water, not about energy. I could really
give a big rats ass if my gas bill goes up by 85 cents a month to have
instant hot. Thanks for your input. The pump setups don't save anything.
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Here's the situation shown on Ask This Old House:
The homeowner had a tankless water heater installed. It was installed
at the opposite end of the house from the second floor bathroom and
the plumber used 3/4" pipe from the unit to the bathroom. The
homeowner used a stop watch to show that it took a full minute to
drain all of the cold water out of the pipe before there was hot water
at the fixture.
A recirculating pump with a push-button control (and a remote for a
second bathroom) was installed under the bathroom sink.
How would a recirculating pump speed up the emptying of the pipes? It
still has to pull all of the cold water out of the pipes before hot
water could reach the faucet. Does it move the water at a rate much
faster than the normal water pressure in the house can move it? If so,
wouldn't that faster flow rate be too fast for the tankless water
heater to heat it up?
I don't know that one would work with a tankless heater because the
tankless needs flow for the heat to come on. The type of loop I
generally see is connected to a standard hot water tank. It has a bronze
circulator pump controlled by an aquastat. In circulating the hot water
off of the top of the tank, it keeps the entire loop hot
Agree with RBM. If it's connected to a button, then I
doubt there is going to be a huge difference in the time
it takes for the hot water to arrive. The pump could
move the water a bit faster than just running the tap,
but it's still going to take time to get there.
If it has a timer and temp sensor, then it can have
hot water there during the hours you set it for with
zero wait. Always thought this would be a good
application for a motion sensor. As soon as you
walk in the bathroom it gets the pump going.
when watching that episode it took approximately 60 seconds without the pump and
what seemed to me to be much, much less time after she pushed the button
of course if the recirculating pump pumps more gpms than the tankless produces
then it doesn't make sense
Modern faucets are infected with Energy Star disease. This means they only pass
water at 2.5gpm, or if they have the particularly virulent Water Sense disease,
A recirculating pump can move much more than that.
Wow, sounds like you're talking about over age 50 prostates. "Only delivers
zzz flow rate, and empties in xxx minutes while standing over the bowl."
I'm soon to be needing one of them recirculating pumps. Cut down on my
Christopher A. Young
Learn more about Jesus
Modern faucets are infected with Energy Star disease. This means they only
water at 2.5gpm, or if they have the particularly virulent Water Sense
A recirculating pump can move much more than that.
On Sat, 11 Feb 2012 12:10:41 -0800 (PST), DerbyDad03
I think the idea is that you press the button when you first enter the
bathroom. By the time you have... umm.... taken care of business, or
are ready to get in the shower, the pump has done it's job and you
have hot water.
You could also use a timer to run the pump for your normal shower
time, with the button as a secondary trigger. Some of the recirc
pumps sense the water temp and stop pumping when the hot water
arrives, so it wouldn't run continuously during the timed perior.
Could also tie to the light switch or even a motion sensor.
As far as flow rate, you could easily double the rate of a typical
shower head and not be an issue with a tankless, as they are always
sized to handle multiple fixtures at the same time. That would cut the
time in half.
Iit's just as appropriate to tankless as to storage type
heaters. It's just an issue of where the heater is located. If
you have a storage type at the far end of the house from a
bathroom, it's going to take a long time for hot water to get there.
Replace it with a tankless and you have exactly the same
How can one guy be wrong on so many things?
You scurrilous pile of shit! To you, everything outside your four walls is
devoid of merit.
I'm going to Manchester on October 15th. I will find you and make you curse
the day you were born, asshole! You will rue the day you embraced
anti-Semitism, anti-Americanism, and all of the rest of the things you
But "dislike" on your part is pretty mild when compared to the hatred on
mine. If I were you, I'd donate a unit of blood to the Red Cross today so
you'll be covered for transfusions later in the year.
True - but as in most things in life, it's a trade off. A recirculating pump
keeps the water in the hot water line hot so that when you open a faucet on that
line you get hot water immediately and don't have to let the faucet run for a
You can also do things to minimize the energy use. Ours is on a timer so that
hot water is available immediately in the morning and evening. The rest of teh
day you have to run the tap for a period of time. You can also wire push button
timers at each location.
Timers, buttons, pumps, valves we have come a long ways from the old
days when water was heated in buckets on the stove top for the once a
I solved my wait for faster hot water in the kitchen by running one
line under the floor to the kitchen sink straight as possible from the
HWT. Looks like its about 25 feet of pipe run now, 1/2 inch CPVC.
instead of maybe 40 feet of old steel pipe that had lots of deposit
build up. I just timed it, 15-20 seconds for the hot water to show up
another 3 seconds for it to be as hot as it's gonna be.
Works for me.
A friend of mine has a setup exactly like the one installed in Ask
TOH but with some extras. It is important to understand that it is
NOT a recirculationg pump one would normally think of. It does
recirculate the wayer, but NOT directly back to the water heater,
but vack into the plumbing system of the house. A few years back IIRC
onASkTOH, a recirculating pump was installed for a tank type hot
water heater. That system did send water back to the heater's tank.
(Someone correct me on this if I am wrong)
My friend's contractor gave him this expplanation on using the
The button (and remote button inthe next bathroom) is there for you
to push IN ANTICIPATION of hot water. It causes water to flow thru
the water heater, thus causing the heat exchanger to begin heating
water and then moving toward the point of demand. The cold water it
is displacing is sent back into the house's plumbing system and not
down the drain. My friend's pump is set to shut off when the pump
input water temp is at the desired temperature. He also had an
indicator light (not sure where) put in to indicate pump activity.
(He had a failure of something in the heater such that the heat never
came on and the pump ran on and on, but since it was hidden behind
towels and such, he never heard it running).
The system does save money, but mostly on gas to heat the water, and
less on water coming into the house and then down the drain.
Which is one of the big problems with them. You wind up with
tepid water from the water heater in the cold water lines. Not
a problem if it's feeding a shower, but if it's the cold water line
for the kitchen that it winds up in, then when you draw what
you think is fresh water you could be in for a surprise. Where
the water winds up depends on the path the water takes
back and what else is on that path.
A few years back IIRC
Don't know about TOH, but it's certainly been done. During
it would be very easy to do.
I guess you save some gas from the fact that the water that's been
sitting in the line and is at say 65F goes back to the water heater
instead of using say 50F incoming water. But in the grand scheme
of things, I don't think it amounts to much. And of course if you
a timer or keep it available 24/7, then you wind up using more energy.
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