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Old 05-17-2008, 11:41 AM   #1
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Hot water recirculation


I'm wanting to install a Grundfos Comfort System pump in my Sister's house. I've used this pump before and have been very pleased with them. My concern is that her house is built on a slab, so her copper water pipes are underneath. Would any of you be hesitant to use one of these pumps on the timer, set to run the pump for most of the daylight hours, and worry about damage to the copper pipes?

Here is a link to the pump.

http://www.grundfos.com/web/HomeUs.n...ag/PAVA-56TMVA

Thanks

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Old 05-17-2008, 02:15 PM   #2
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Being on a slab, if not already present, how would you plumb the return feed?

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Old 05-17-2008, 03:37 PM   #3
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Hot water recirculation


If you look at the link provided, it shows the piece that goes under the lav sink at the longest run from the water heater. Thats the great thing about this setup, no return line needed. Just not sure on possible damage to pipes.
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Old 05-17-2008, 04:42 PM   #4
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My bad. I clicked on the "how it works" link and saw this:
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Old 05-17-2008, 06:33 PM   #5
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Cjett,
Those Grundfos pumps work great, don't they? Unless your sister's pipes are in really bad shape I wouldn't be concerned about damage to the piping.

The only problems I've seen with these pumps on slab houses have been when the cold water comes out warm due to heat transfer. I know this sounds crazy and I have only seen it once or twice but the I have seen it. There are so many variables that could contribute to this that there's no way to know what actually caused it. It's just something to watch out for.
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Old 05-17-2008, 06:37 PM   #6
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I personally wouldn't reccomend it in this situation.... We ALWAYS use L copper for recirc systems. Even if you do have L copper under the slab, there is no telling what shape it is in down there, whether joints were wiped when they were soldered, or if cut ends were reamed. Flux left on joints can contribute to premature corrosion, and unreamed cuts cause turbulence in the line and wear out the line much more rapidly.
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Old 05-17-2008, 06:49 PM   #7
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These retro fit circulation systems only move the water for a brief period of time per cycle. There is a thermostatic bypass valve that opens when the hot water temperature at the fixture has dropped and closes as soon as the cooled water in the hot side has been pumped into the cold side. In addition, the flow velocity is fairly slow when it is moving, so it's probably harmless.
Alan is right, most plumbers use Type "L" copper under slabs. The good news is that much of the time "soft" copper is used and there are no joints underground to be affected.
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Old 05-18-2008, 09:48 AM   #8
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Angus, you are right, that picture was for the system for new construction.
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Old 05-18-2008, 09:57 AM   #9
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mstplumber, are you sure about the thermostatic bypass valve? I was assuming that the part that goes under the lav sink was basically just a check valve, and hot water flowed any time that the timer on the pump was active, am I wrong?

Yes they work great and I have not seen a big problem with warm water on the cold side. These would be a big seller if more people knew about them, especially in drought areas, saving all of the wasted water waiting on it to get hot.
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Old 05-18-2008, 11:13 AM   #10
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Quote:
Originally Posted by cjett View Post
mstplumber, are you sure about the thermostatic bypass valve? I was assuming that the part that goes under the lav sink was basically just a check valve, and hot water flowed any time that the timer on the pump was active, am I wrong?
Thats what i thought too. Maybe there are other kinds that I haven't heard of.
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Old 05-18-2008, 12:38 PM   #11
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I tried this is my house which is slab. it was a total waste of money. The hot water was cold after about 30 sec of turning off the faucet.I would recomment a small tank under the sink or some type of electric tankless water heater under the sink.
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Old 05-18-2008, 02:05 PM   #12
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According to the installation documentation on Grundfos' website, when the water at the bypass valve, they call it a "thermal bypass", the flow should stop. I can't find the exact temperature range on the website but I seem to remember it is somewhere around 95 - 100 degrees.

One thing to remember, if the pump isn't running the water will cool off pretty quickly. I think the timer can be set for 3 different periods. I have installed several of these systems and, while not quite as effective as an actual circulation system with a separate return line, they are a huge improvement over nothing at all.
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Old 05-19-2008, 03:11 PM   #13
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mstplumber, are you saying that the adapter under the sink stops the flow of water? Then does the pump still try to pump anyway? I'm getting a bit confused at this point.
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Old 05-20-2008, 08:02 AM   #14
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cjett,
That is exactly what I'm saying. Just to be sure I called Grundfos (1-800-333-1366). The way the system works is that the Thermal Bypass has a heat sensitive plastic plug inside. When the water temperature at the bypass drops to 98 degrees (+/- 5 degrees) the plug shrinks and allows the water in the hot line to be pumped into the cold line, as long as the pump is on. As the water temperature at the bypass increases the plug gradually swells, blocking the bypass. The plug never completely blocks the bypass, allowing a "trickle" of water through the whole time the pump is running, which is apparently enough to keep the pump from overheating but not enough to keep the water hot.

So, yep, the pump runs even when the valve is "closed".

I can tell you that on the ones I've installed, when you turn the cold side on it's only warm for a second or two, so it must be a very small "trickle" that gets through.

Also, since the system is static when the pump is off, there is no problem if the plug shrinks.

One other thing. If you are comfortable soldering this is a pretty easy DIY project. Just make sure to follow th instructions with the pump. The pump goes on the Hot water pipe with the direction of flow AWAY from the Water Heater. The bypass valve is a piece of cake to install.

Hope this helps.
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Last edited by mstplumber; 05-20-2008 at 08:04 AM. Reason: bad typist
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Old 05-20-2008, 08:40 AM   #15
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mstplumber, thanks that is great to hear. I emailed Grundfos two or three months ago with questions about this pump but never heard back. I wasn't ready to use one at the time so I never pursued it. I wish Grundfos would include all of that info on their site.

That trickle should not be hard on the pipes at all. I doubt that it would hurt anything to run the pump 24/7 when that would be all it's doing most of the time, although I don't plan on doing so.

I am in the HVAC biz and have no problems sweating pipe or installing the pump. Thank you very much for going out of your way to obtain all the answers to my questions.

Yes, it helped a lot!

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