How do I hook up a hot water gravity return?

[poison_1024]

I just ran some water lines from the basement to the garage - about 75 feet or so. I ran an extra 1/2" line because I want to feed the hot water line back to its source so that you don't have to wait five minutes for the water to become hot.

Do I just tee off the hot water right before it goes to the fixtures and then attach the other side of the return line to the input side of the hot water heater? I guess this would keep both the hot water line and the return line hot when the faucet was on but as the water starts to cool it will return to the hot water heating in the return line when the faucet is off.

Would putting a one-way valve in on the return to the water heater or maybe that will cause problems with the cold side water pressure? Anyone know?

[Grandpa]

Hmm, Google is your friend:

"Gravity hot water recirculating loops that do not require a pump can sometimes be installed after a house is built. They will only work when the water heater is below the water supply lines. This system requires that the hot water line return back to the heater after it services the farthest fixture. The return line connects to the bottom of the water heater at the drain valve. Natural convection drives the system. Energy loss is a minimum if you insulate the entire hot water loop except for the last 15 feet of pipe as it re-enters the water heater."

More info here:

[poison_1024]

here:

I got that much but now my concern is that the path from the heater to the farthest point is not a constant uphill climb. It goes up then down a little then back up around the corners then up then down. The net change is definitely uphill.

[Grandpa]

here:

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Sorry I thought you asked where to connect the return line. The site tells you that it might work if you connect it to the drain valve. That will at least maximize the thermal gradient. Whether it works for you or not depends on how much of a gravity drop you actually have. Think about the flow and try to eliminate any thermal "hills" especially on the return leg, turns left and right aren't much of a concern. The damn transistors burned out on my crystal ball a few years ago, and I haven't been able to find replacements for looking at your set up.

[Steve Barker]

The house I grew up in was done this way. The return "T's" into the drain port, and you should have a flapper type check valve in that vertical line. This will keep cold water from being "pulled" back towards a faucet when you open it. Be sure to get a flapper type and not a spring loaded one. Try to keep the return line headed down hill even if just a slight amount. Most of the "gravity" work will be in the vertical line down the side of the tank. Keep it a few inches from the shell of the tank to allow it to cool better. These are great systems and very nice especially if you return it from your clothes washer also, so it gets hot water the second it comes on.

[trader4]

Having a 150 foot loop of hot water pipe constantly circulating to provide fast hot water to a garage doens't sound like a good idea to me for energy reasons, even if it would work. I'd get one of the small pumps you connect at the garage end with a button you can push that then quickly pumps water from the hot pipe back into the cold pipe until it gets hot water. Using X10, you could also rig this so the pump goes on based on a motion sensor when anyone enters the area, so you don't even have to push a button.

Alternatively, there are pumps that will keep it constantly hot, using similar idea, but also offer timers, so you don't waste energy for most of the day when you don't need it hot on demand.