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Cold water return for a hot water line Bob 07-20-2005
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Posted by Jeff Wisnia on July 20, 2005, 11:21 pm


Bob wrote:
> This is my first visit to this group, so the question may be a repeat.
> I am thinking about installing a return pipe on my hot water feed to the
> kitchen to reduce the amount of cold water that is wasted before the hot
> water has reached the sink.
> Where is the best place to make the connection close to the hot water
> tank? It takes nearly four litres of cold water to run through the pipes
> before the hot water arrives. I have lots of pipe and connections left
> over from different projects and I might as well use them for this. My
> ceiling is easy to access. My problem is knowing where to connect near
> the tank.
> I have also read that some people have installed a "U" near the tank to
> reduce the loss of heat when hot water is not being drawn for use.
> Anyone have any details about this idea?
> Many thanks for your ideas.
>
> Bob

You can create a thermosyphon by bringing a return back from the hot
water line near the faucet and connecting it to the bottom of the water
heater through a "swing check valve". That valve will prevent cold water
from moving towards the faucet.

But keep in mind that unless you insulate the piping you'll be
constantly leaking quite a bit of thermal energy from the system which
will have to be replaced by using additional electric or gas.

You can use a amall circulating pump controlled by a timer or proximity
switch and also a temperature sensor so that it only runs when the water
near the faucet is below a preset temperature and when you expect to be
in the kitchen (timer) or when you are actually in it and moving around
(proximity sensor). Again, insulation of the piping will avoid wasting
too much energy.

There are some systems which use a small pump under the sink controlled
by a similar temperature sensor and timer or proximity switch which push
the water from the hot water line back down the cold water line. These
do work, but if you want to draw a glass of cold water, you have to
waste water while you drain off the warm water in the cold water pipe.
Again, insulation of at least the hot water pipe will help save energy.

All in all, I'd suggest you do the math and try and calculate how much
the water you are wasting will actually cost, and compare that with the
added energy you use and the amortization and maintenance costs of
whatever "immediate hot water" recirculating system you decide to use.

Chances are a "local" point of use instant electric water heater will
end up costing you less in the long run, and won't "waste" any water.

Jeff

Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."


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Posted by kevin on July 20, 2005, 8:56 pm


I really have to wonder if any of these solutions would save any money,
even in the long term. Water is typically very very cheap. Electricity
& gas not so cheap. Buying instant electric heaters and what not are
even less cheap. And paying for repairs, even if it is just one leak in
a lifetime, could put you forever in the red on this project.

I have seen claims that the average family wastes 27 gal of water a day
waiting for hot water. I can't even fathom that. We waste, maybe, 2 gal
tops a day. E.g., I wait about 10 seconds before getting in the shower.
When washing dishes (2-3 times a day), I rarely ever wait at all, as
the water isn't that cold to begin with.

On the environmental side, pouring a gallon of water down the drain
once or twice a day might not be such a big deal when compared with
manufacturing a hot water heater, or drilling for gas, or burning coal
for electricity, etc. In many cases, the water will just go right to a
septic or greywater system anyway.

Why not just go get some cheap pipe insulation, put it on your hot
water lines, and see how it works? This is doable for probably less
than $10, and 15 minutes of effort.



Posted by Bob on July 21, 2005, 8:54 am


kevin wrote:

> I really have to wonder if any of these solutions would save any money,
> even in the long term. Water is typically very very cheap. Electricity
> & gas not so cheap. Buying instant electric heaters and what not are
> even less cheap. And paying for repairs, even if it is just one leak in
> a lifetime, could put you forever in the red on this project.
>
> I have seen claims that the average family wastes 27 gal of water a day
> waiting for hot water. I can't even fathom that. We waste, maybe, 2 gal
> tops a day. E.g., I wait about 10 seconds before getting in the shower.
> When washing dishes (2-3 times a day), I rarely ever wait at all, as
> the water isn't that cold to begin with.
>
> On the environmental side, pouring a gallon of water down the drain
> once or twice a day might not be such a big deal when compared with
> manufacturing a hot water heater, or drilling for gas, or burning coal
> for electricity, etc. In many cases, the water will just go right to a
> septic or greywater system anyway.
>
Good comments. I often try to calculate the total "cost" for
my actions from the environmental side. I can not justify
buying a new or newer car to save a small amount of gas. I
just drive a little less. As for this idea, it is not
critical - the little water that I "waste" dilutes some of
the real waste water that is in the system so it does serve
a purpose.
> Why not just go get some cheap pipe insulation, put it on your hot
> water lines, and see how it works? This is doable for probably less
> than $10, and 15 minutes of effort.
>
The hot water line is already insulated. Whatever heat
escapes ends up contributing to the heating of the house so
the energy is not lost completely.

thanks for the comments.

Bob


Posted by on July 23, 2005, 3:27 am


> the little water that I "waste" dilutes some of
> the real waste water that is in the system so it does serve
> a purpose.

if you have city sewers, the water-treatment-plant operators would
tell you a different story. The more water becoming septic, the higher
everyone's taxes will be.

In other fora is discussed the fact that, it not only is cost-effective
to keep water away from human excrement, but it's actually
cost-effective to keep urine separated from #2, right from the git-go.



Posted by Edwin Pawlowski on July 21, 2005, 2:07 am



> I am thinking about installing a return pipe on my hot water feed to the
> kitchen to reduce the amount of cold water that is wasted before the hot
> water has reached the sink.


Do you meat a re-curculting line that keeps the water in the line hot all
the time?

There will be a net lo$$ in the end. Having instant hot water is nice, but
the little bit that goes down the drain is cheaper than keeping the pipe hot
all the time.

If you are somehow using this only when the water is turned on, there may be
some saving.






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