I was watching this old house and they were installing a tankless water
heater. And to over come the delay a recirculating pump. The solution to
having the pump run all the time was to install a motion detector in the
bathroom which would signal the pump to start.
What was it recirculating? Cold water?
If it was truly tankless, the idea is not to have the burner or
electric coils come on unless you need hot water. There is nothing to
keep the water hot for long periods of time when the burner is off.
The unit should be installed close enough to the point of use so that
the delay is minimized.
Recirculating loops work OK for conventional (tank) systems, although
they should be insulated unless you like spending money to heat the
interior walls 24/7/365.
Personally, I prefer a conventional system with the design of the hot
water heater as close as possible to the critical points of use
(bathroom - kitchen, etc.)
No, the hot water, the pump removes the standing cooled water in the
pipes between the tankless heater and the point of use. Of course, it
does nothing to deal with the "cold water sandwich".
TOH is doing a totally "green" renovation is Austin. Something we are all
going to have to do someday. We have a drought situation in California now
with voluntary conservation being sought and with the cost of energy always
going up the tankless heater will be used more and more. Someone a few
weeks ago was asking how to deal with the delay of getting hot water I just
thought I'd share a solution. It also reduces the cost of running the recirc
pump to when someone enters the bathroom.
On May 2, 12:43 am, firstname.lastname@example.org (Beachcomber) wrote:
Unless you are going to have multiple units, which is cost and install
prohibitive, in many cases in a typical house it's not going to be
possible to locate a single unit close enough to all the important use
areas. That's why the pump makes sense, just as it does for houses
with a conventional water heater.
The system under discussion doesn't circulate water 24/7. It starts
the pump when someone enters the bathroom. Other systems use a push
button. So, they are not that different in the need for insualtion
than a system without the pump.
Sounds more like a convenience rather than something that is
energy efficient. So there is a 5 second delay to your hot water.
What's the big deal? The cost of polluted water is still cheap in
most areas. Adding a circulation system and the extra copper
(or plastic if you like) seems more like a loss in the long run.
Not to mention the added price of its repair over the years.
If your house is so large that it takes even longer than that, your
going to have to install multiple units because of your water demands
cant be handled by only one machine.
On May 3, 8:26 am, email@example.com wrote:
If it was only 5 secs, it wouldn't be much of a deal at all. In
fact, even with the pump system under discussion, it's likely still
longer than that. However, it's very common to have delays of many
times that in a large 2 story house.
The cost of polluted water is still cheap in
The pump systems like the one being discussed go close to the faucet,
like under the vanity. The only extra piping is between the cold and
hot water lines under the sink.
No different than most other home convenience items.
An upstairs bath in a typical mid range 2 story home commonly takes
longer than 5 secs to get hot water. And tankless are available that
will deliver 10+ gal a min, which is a lot of water. At that rate, a
50 gal conventional would be gone in 5 mins and you see lots of
3000-4000 sqft homes with only one 50 gal tank. So, you can certainly
have a fairly big house with only one unit. However, using 2 units
would be an option and could help reduce the delay.
Using 2 units will almost always reduce the delay, because the units
are then almost always located closer to the faucets. For example,
you'd typically have one unit in the basement close to the downstairs
baths and then another one upstairs or in the attic, close to the
We have a one story house, with the water heater about 40' from our master
With low-flow shower heads and 3/4" main supply lines, it takes well over a
minute for the hot water to reach the shower head.
Thankfully, I installed a recirculation system when I plumbed our house,
which circulates the water to a point just under the shower floor. Even
with the recirculation system running, it can take 5-10 seconds for hot
water to make the trip from under the floor to the shower head.
Our recirculation pump runs on a timer, so if we take a shower during the
usual "off" time, it's a long cold wait for hot water, with a lot of water
just going down the drain.
If you have a basement, you might be able to use a recirculating
thermal siphon instead of a pump. (For possibly less energy and
maintenance costs). The idea is that hot water rises because it is
less dense and by the time it gets to the top of the riser pipe, it
will cool and sink down the recirculating pipe. Of course, good pipe
insulation is recommended.
Many multi-story apartments and condos are plumbed this way.
I already have the pump installed and working well, so I don't have much
reason to change it now. Compared to the rest of our energy use, the recirc
system doesn't use much.
In any case, I thought thermal systems relied on the water heater being at
the bottom of the loop. In other words, the hot water rises from the water
heater, up through the pipe, then comes back down the recirc line as it
cools on the other end.
Assuming that's the case, we don't have a basement, so the water heater is
higher than most of the fixtures using the hot water. And we have vaulted
ceilings throughout the house, so we don't have an attic to run the recirc
line up through either.
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