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Domestic Hot Water Recirc - rattle rattle rattle

Just completed a DIY domestic hot water recirculation system and it's working well...except for the rattle rattle. It's most noticeable at the hot water outlet pipe, but reverberates throughout the house and is most noticeable in the bathrooms. BTW, this is an 80 gallon concrete tank with a bottom cold water inlet. Questions:
- Is it air? I don't think so, as that would ultimately come out of the faucets, right? I also don't see any bubbles in the transulucent PEX I used.
- The tank states it has a cold water diffuser on the input, so that could potentially be the source.
- I can minimize the rattle by reducing the flow with the ball valves on either side of the pump, that seems to help, but at some point that will impair the functionality, i.e. it will take a long time to distribute HW after the system turns on, or the water may cool down on its way through the system. Am I harming the pump? (Grundfos UP10-16)
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- Can I reduce the transmission of the rattle by inserting a few feet of PEX on the hot water outlet? That should minimize the sound transmission throughout the house. Does that make any sense?
Thanks,
Kyle
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Comments
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
The reason it reduces when I throttle the flow is that with reduced flow, whatever is causing the rattle is moving with less energy.
I doubt I can eliminate the rattle, except for really reducing flow, or limiting its transmission somehow, perhaps with some PEX in the HW line.
or vice versa, too small of a check and gravity flow opening and closing the check valve.
or could be a swing check and should be a spring check......
Dave H.
trainer for Caleffi NA
Living the hydronic dream
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
Yours, Larry
"The Vaughn water heater is constructed with a heat trap installed within the water heater’s hot water outlet connection. This device helps prevent heat from escaping through the storage tank’s hot water outlet during standby periods, resulting in improved operating efficiency. The heat trap is constructed from a specially designed bronze nipple with an internal floating ball that during standby periods of no flow settles and closes off the storage tank thereby preventing thermal conduction of hot water radiating through the hot water outlet."
The heat trap is inside the envelope of the tank, within the foam insulation. So a non-serviceable design - stupid.
Unless anyone has any brighter ideas, at this point I'm going to live with it (noise is not an issue at the heater itself), and insert a section of PEX just after the heater to minimize the transmission of the rattling throughout the HW pipes in the house.
Thanks!
Rick
On some of those old tanks, not much of the nipple extended above the jacket, sometimes just the thread. So removing may damage the nipple.
trainer for Caleffi NA
Living the hydronic dream
Seems risky though. I don't know what the other end of the nipple looks like, and if I can't get it out, and destroy the threads in the process, I'm screwed.
I lobbed an email into the manufacturer about removing the heat trap. We'll see if I hear back.
Yes it is possible to collapse that end and still not have it removed.
I suppose a long punch could drive the ball into oblivion
trainer for Caleffi NA
Living the hydronic dream
Rick