Remember, you are going to have to have an external pump to do this because the pressure in the cold water line is the same as the pressure in the hot water line.
To have instant hot water, the pump must operate continuously. This is a valid technical solution to your problem, but a costly one.
I would suggest that you put a flash hot water heater at the point of use. That way you wouldn't need to use energy until you are ready to use water.
On the other hand, 4 litres of water doesn't cost much. It is about the same as flushing a toilet.
In my house, I have installed a smaller hot water heater in series with the hot water line at the point of use. It doesn't work nearly as well as a flash heater, or the recirculating pump that you propose, but it works well enough....
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.
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.
That connection doesn't necessarily need to be hooked near the hot water tank. A short run straight to the cold feed for the kitchen and a pump in that run would work and could potentially be much easier to install. The pump would move the 'stale' water from the hot water line through the cold water line back to the heater. I believe there are kits with thermostat controlled pumps even for this kind of hookup. Then the pump doesn't have to run all the time.
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."
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.
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.
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.
Interesting little machine, but not economical for me. I don't pay for the volume of water that I use - flat annual fee and electricity to heat the water is about $0.07 per kw hour (cdn) so I would have to llive a long while to pay for the little hot one. Thanks for the link. It never hurts to know what is on the market.
On mine, I had a nipple put between the tank and the drain, and plumbed the return line into that. Yes, it will mean a little extra work when the heater has to be replaced. I save a lot of water because the supply line across the basement is 3/4 inch, and around here the water rates have gone up far more that gas or electricity. I insulated the supply line and left the return uninsulated, and it works well without a pump, but I have a lot of vertical line to the upstairs bathroom where the crossover is, and I'm sure that helps.
Its true that there is some heat loss, but where I live we have far more heat> This is my first visit to this group, so the question may be a repeat.
If you're only recirculating the kitchen line, I doubt you'll save enough water to matter.
I installed a recirculating system in our house, for convenience, not energy savings. With long 3/4" supply lines and low flow shower heads, we were waiting well over a minute each morning for hot water to reach the far shower. While it did waste a lot of water, it simply wasn't convenient. After installing the recirculating system, we have hot water in about 5 seconds (nearly instantaneous on the full flow tub faucet).
Usually, the return line is plumbed into the drain valve at the bottom of the hot water tank, with a tee for the drain so you can still empty the tank. But, my tank sits in a small alcove down in a deep drip pan. So, I couldn't make a connection there. Instead, I put a tee on the cold water inlet, and tied my recirculation line in there. It requires a check valve in the return line, valves to turn off and bleed air out of the return line, and of course a pump (though there are methods of making thermosyphon recirculators). My recirculation line is 1/2" and I used a Grundfos pump with a built-in timer. It runs a few hours in the morning, and a few hours in the evening to cover most of our likely showering times.
Other than the regular insulation in our floor, I did not insulate our hot water lines. When the pump is running, it's easy to tell there is heat loss from the hot water and recirculation lines. The floors above the pipe runs are warm, like radiant heat. Feels nice on cold mornings. :) But, it is an energy loss. It also warms the cold water lines a bit that run close to the hot water lines. So, we have to run the cold water a few seconds when we want really cold water. Compared to the rest of our energy use I haven't noticed any major change in our electric bill (we're all electric here).
We're on a private well, so I have to think the energy loss from the recirculation system is offset by not having to run our well pump as often.
Heat rises, so if your tank is lower than your fixtures, it might be a smart idea. In my case, the hot water tank sits above all the plumbing runs in the crawlspace. So, it makes a "U" naturally by coming up out of the top of the tank, and heading down to the crawlspace below.
Without going into the invoice pile, I recall that it is $120 or $180 per year for a single dwelling. Enough for us because we don't waste/use a lot of water, but for people who want everything to be green ans clean (cars, driveways), it is not enough.
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.
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