Continuous circulation to avoid pex noise!

Sammy_dogson · April 2021

Hello All, I’m a big fan of the forum and have learned a ton from all you here, so thanks in advance for your help. THIS SHOULD BE A FUN ONE!

I recently installed a radiant heating system in my house. The ground floor has a warmboard type system (eco warm) and the second floor is traditional staple up with some flimsy aluminum plates that went in after the pex tubing (1/2” oxygen barrier pex). The good news is that both kept my house warm all winter, the bad news is that the second floor system snap crackle pops to hell and back. Whenever the boiler turns on.

To save everyone on here some time, I know why it’s happening . I also know that the only way to minimize this, short of moving out of my ground floor, ripping out the ceiling/Insulation and inspecting each of the 20+ clicking areas and fixing them (likely resulting in replacing all 6 runs of tubing) is to run the system on continuous circlulation with an outdoor reset.

Sounds simple right? Well, maybe for some systems, but I have a Navien NCB-240. On top of that, I have a 1800sqft house in Long Island, NY and from my understanding, this boiler is far too powerful for my house, at least on the space heating side.

For all asking WHY that size boiler, the plumbing contractor claims that he didn’t need to do a heat loss calc because he sizes these combi boilers based on the hot water demand. Now...he never went over my DHW demands with me but his company was sick of callbacks relating to people not being able to run two showers at a time, or a washing machine and a shower and a sink etc etc....so they just oversize, thinking nobody is close enough to their boiler room to realize they short cycle day and night (especially night in my case)!

So, all in all, I have tried to ride the curve and set the built-in outdoor reset the lowest settings possible to keep my house the perfect temp but never hit the set point on the thermostat. HOWEVER, the boiler is just too powerful and it can’t actually produce such a low deltaT (9-11) over the 9 loops totaling 1600+ feet in my house, so the boiler starts to creep up from its set point, one degree at a time, until it shuts it self off. This can happen every 5+ minutes or so at its worst, which means, yes, you guessed it, a 2 minute symphony of clicking that can happen like clockwork nearly 10 times an hour. It’s like trying to sleep through that feels like some distant cousin of Chinese Water Torture. Each time I start to drift off, it’s back again. Luckily my wife sleeps like a rock but me...I’m struggling fellas!

My plumber is not of the caliber to help me on this, and he’s the best in town sadly. I’ve asked many local plumbers to help and none have came up with anything. I’ve called Navien and tried to adjust all the settings surrounding shut off but to no avail.

I thought maybe a buffer tank might be a solution? Anything would be welcomed and appreciated. Thank you all!

-IHB

Dave H_2 · April 2021

I would suggest a buffer tank, that's what they are designed for. The boiler will only fire (and fire for a long time) to maintain a temp in that tank. The heating will then draw off that tank rather than the boiler that has a very small amount of fluid in it. Buffer tank size will depend upon several factors as in smallest firing rate of the boiler and the smallest zone in the system.
Here's the good thing, they can never be too big but if the tank is too small, you can still achieve the short cycling issues.
Take a look here, this webinar discusses piping these boilers in and also sizing a buffer tank towards the end

hot_rod · April 2021

Determine the load of the smallest zone. Can the boiler be locked at the lowest firing rate in heat mode?

So to address the short cycling use the buffer sizing formula for a sizing suggestion.

A couple of piping examples for true constant circulation.

You may not completely eliminate the ticking, as anytime you have a temperature change the plates will squirm somewhat, the constant circ would be you best "after the fact" correction attempt.

I guess it comes down to how much you want to spend to minimize the cycling and noises?

Jamie Hall · April 2021

All of the above. Plus -- use recirculation on the second floor loops. Have a thermostatic mixing valve with the cold inlet being the loop return, the hot inlet being from the buffer tank, and the outlet going to the loops through a dedicated circulator (doesn't have to be huge pump!). The rest of the return goes back to the buffer tank. Ideally the mixing valve would be controlled by the outdoor reset -- or a different one -- but in practice you can probably dial the thing in to maintain comfort almost all the time with a constant thermostatic setting.

HomerJSmith · April 2021

When I used plates, I always used Talcum powder on the tube guides so that the pex could slide on the plates as the pex expanded. Talcum is gone, so I have used corn starch, instead.

I have entertained the idea of using Silicone spray, without petroleum distillates on the plates, such as Sprayway Silicone spray. However, I wonder if it would affect the pex.

Not much you can do except live with the noise.

hot_rod · April 2021

Ideally the tube should not move in the plate and the expansion should be in the loop ends. The ends need to be free and have room to move.
That was always the best feature of the Radiant Design ThermoFin, a very tight fit. It takes some force to snap the tube all the way into the channel.

A soft tip on a palm nailer is the way to go, if you do a lot of footage.

Zman · April 2021

I suspect that your noise is being caused by the boiler's internal on/off differential of 20 degrees or higher.

I would suggest a buffer tank with a smart mixing assembly that is carefully designed to hold a very precise and steady supply water temp. You could try just using constant circ and ODR and see if you could dial it in.
Another option would be to introduce indoor temp feedback to the system so that the water temp could be adjusted for both outdoor temps and what is really happening indoors. The trick here is to keep the water temp very stable. Careful valve selection, perfect water sensor placement (in a well with thermal paste) and smart controls are the key.

@Mike_Breault from Tekmar has been spending some time on the forum. I'll bet he has a solution

As they say back East, those Tekmar folks "Ahh Wicked Smaaat"

Mike_Breault · June 2021

Thanks @Zman the wall has a great variety of "wicked Smaat" folks..

Hot rod had a great post, and a buffer tank would indeed help, tightening the DeltaT could help, but remember it will change the required flow rate for BTU delivery,

plates should have 6-12" between them, so some expansion happens there, not just at the ends. alternatives are Onix by watts radiant (0 expansion- just remember to have the right water chemistry. clean distilled and proper Ph. there is a wholesaler in TO that sells more Onix than anyone, and for high end homes in Toronto as they only do radiant,and never want noise. you will hear mixed reviews on Onix. but generally, its a good product when done right)

if you cant get it tight enough, loosen the plates a hair. generally the noise is more from the wood floor agains PEX.

ultimately, drop the combi. get a boiler and an indirect for Domestic and right size those items

Best

Continuous circulation to avoid pex noise!

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