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?
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:
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.
"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.
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.
I plumbed my entire 3 flat myself and put a return line to the bottom of each tank. Sweated copper. Completely well worth it. Anyone that tells you differently is foolish. With pex tubing & connections, the job is significantly easier and cheap.
