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Once I saw on an episode of This Old House that they were putting in hot water return lines: pipes that recirculate idle hot water back to the heater so you get hot water right away, instead of wasting time and water.

My wife and I are looking to getting our first home and I think this might be a beneficial investment to make at some point. I also am skeptical of the cost.

Is it worth it to install them? Or is it a matter of convenience?

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3 Answers 3

up vote 7 down vote accepted

After doing a bit of research on what exactly hot water return lines are I found this page which goes into a lot of detail about how they work and their benefits and drawbacks.

The big drawback I see is that you will need to make sure that all your hot water lines are well lagged to minimise the inevitable heat loss that will occur with the hot water sitting in the pipes. Otherwise you will be heating water for it to go to waste when you aren't using it.

So you will need to add up all the costs:

  • extra pipework
  • lagging to minimise heat loss
  • extra redecoration where you've worked on the pipes
  • the extra heating costs
  • etc.

and decide whether it's a fair price to pay for instant hot water.

Another alternative would be to change the pipework so you don't have any long runs or even install secondary heaters for parts of the house.

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I vote for the 2nd water heater. If your house is big enough that it takes a long enough time that you are worried about water consumption, then it is probably worth it to have 2 water heaters on different sides of the house. –  Kellenjb May 2 '12 at 23:55

"worth" would be your call. How important is it to you that the water is hot instantly when you turn on the tap?

The benefits of a circulating pump is that you aren't wasting water waiting for the hot water to come. The drawbacks are that you are wasting energy constantly circulating and re-heating water you aren't using.

If you use a lot of hot water, one alternative to consider is a tankless on-demand heater installed near the faucet.

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If you have the walls open and access to the pipes anyway (say you're doing a full kitchen reno), it can be a worthy project. Just like ChrisF said, the hot water line must be well-insulated. I actually think the return line SHOULDN'T be insulated, because as it's allowed to cool it will pull heated water through the loop by convection. This will provide hotter water faster at a cost of running your tank heater more.

If you don't have access to the pipes, there are still a couple of options. The Hot Water Lobster is a flow-control valve that goes between the hot and cold supply pipes of the furthest run from the tank. When the water on the hot side drops below a settable temperature threshold, the valve opens to allow the cooled water to return through the cold water leg (which after all is connected to the HWH as well). The downside of this system is that your cold water will be warmer, and it's not as efficient as a dedicated return loop.

You can also use an electric point-of-use heater, like this one. This will hook to the supply line under the sink (or wherever) and keep a small amount of water ready for instant use, which should be enough to last until the hot water from your main HWH gets to that faucet. The one I linked to only draws 1500W, which is just a little more than a 15A breaker should have on it (80% of breaking amperage = 1440W, but theoretically the breaker won't trip until 1800W). So, you'll want a dedicated 20A breaker for a heater like this.

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The problem with the Lobster is that it's circulating water from your HW tank into your cold-water drinking lines. Lots of folks recommend you never drink the water coming from your HW tank due to lead: seattlepi.com/lifestyle/health/article/… –  DA01 May 2 '12 at 15:57
    
Whether that's a concern depends heavily on the age of your house, and what's in the plumbing (and solder). Homes built in the late 80s and later use copper pipes and lead-free solder (though there was a period of a few years where PVC supply pipes were used, and much like lead hot water leaches BPA from the PVC faster than cold). I agree it's a concern, but if you can verify the plumbing materials in your home you can avoid hazards related to drinking hot water. –  KeithS May 2 '12 at 16:15
    
And in any case, a return loop will bring water that's been through the hot water line back to the cold-water line feeding the HWH, and that can result in its use as cold water anyway. That's less likely to introduce significant lead into the cold water supply, but it can still happen. –  KeithS May 2 '12 at 16:16
    
The use of the cold water is a good idea, the affectiveness of convection to get the water to circulate is very dependent on the plumbing in the house , you could look at a pumped system that does the same but with a circulating pump –  UNECS May 2 '12 at 21:26

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