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Old 08-21-2007, 03:39 PM   #1
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Hot Water Recirculating Loop


I'm interested in installing a hot water recirculating loop. The location that my current plumping runs in the basement is primarily below the joists (aka, it's attached below them) but it makes a step up between them to run over the HVAC ducting. My return hot water run will need to make this same step. It will therefore be the high spot in the run.

In an ideal world I'd like to go with a gravity system, but as I understand it you have to have to be careful of high spots that collect air. If I installed a pump (like a Grundos UP10-16) do I still have the same problem? Is there a way around this (an no, there is not any reasonable way to avoid the way the pipes are routed.)?

Thanks in advance.


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Old 08-21-2007, 04:16 PM   #2
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One solution may be an auto-bleeder. Installed in the high area, they allow air to bleed off but close when hit with water. Just a thought.


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Old 08-21-2007, 05:50 PM   #3
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This would only be a problem that would work itself out in a short time. If you have air trapped in the line when you fill it, it will soon become dissolved in the water in the line. This is why the old air cushion type water hammer arresters quit working after a short time. The air dissolves into the water. Don't worry about the air. You might worry about being able to drain the pipe completely if it is one that you must do to avoid freeze damage if water is trapped in the loop.
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Old 08-21-2007, 08:06 PM   #4
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If you use a pump and check valve to keep it flowing in the right direction you don't have to worry about "traps" in the piping. Don't use an autovent on potable water.
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Old 08-22-2007, 05:44 AM   #5
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Travis, re my post yesterday to your question, I assumed that you were speaking of an open system, i.e. domestic hot water recirculation system. If so, my post stands as is. If you are speaking of a closed system however, the air must be removed as you fill the piping system since there will be no additional water added that can "absorb" the air trapped in the loop. This can be done with a small manual valve located at the highest point, or with an air removal fitting that is designed for this [a pricey way of doing this for something so seldom used, only if you drain and refill your piping[.
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