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Noisy Radiant Floor Heat

When remodeling a room on the first floor of my house, I added radiant floor heat to the room. To do this, I added a layer of 3/4" OSB on top of the original subfloor and routed a 3/4" groove to accept 1/2" pex pipe. After installing the pex pipe, I added a layer of 7/16" OSB to the top before installing a laminate floor. This heats well and is quiet. I have now done the same heating arrangement to my second floor. While it heats well, it is noisy. This is a problem because our bedrooms are on the second floor. While the boiler is running, the noise is a nearly constant light popping sound. When the boiler stops and the floor starts to cool down, the noise is less frequent. I attempted to bleed all of the air out of the lines, but do not know if I have been successful. Is air in the lines a possible cause of the noise, or is it more likely that the noise is a result of expansion and contraction of the PEX pipe? Any help you can offer would be greatly appreciated.

Thank you

Re: Noisy Radiant Floor Heat

This sounds like expansion noise rather than air noise, and has become a persistent problem in installing radiant floor heat; air noise sounds like water flowing thru a pipe or a "gushing" sound as the air & water inside the PEX fight each other to get thru the pipe.

Expansion noise is caused by the expansion of the outer surface of the PEX rubbing against the OSB as the PEX expands (as all PEX does) when it is heated.

In response to this common problem, the PEX mfgrs have come out with PEX tubing that has a low friction outer layer that alleviates this problem; Watts brand makes a RadiantPex for this purpose :


There are aluminum channel strips that are supposed to be used when installing floor radiant & are usually inlaid into the cut groove in the OSB & serve as a heat reflector, as well as a slippery surface that greatly reduces expansion noises.

I don't know if there is a remedy short of ripping out the floor & starting over, but you deserve a lot of credit for the work you've done to install this yourself---do some further research before you give up on the upstairs floors; there is a dedicated forum for radiant floor heat at:


Click onto "Ask Questions" then scroll down the options & click onto the radiant heat forum.

Likewise, at:


Also Google "radiant in-floor heat noise"

scroll down to the "heating help" entry for an article on this problem.

Also Google "contact noise in radiant floor"

Also Google "expansion noise" radiant floor heat

Also Google "radiant floor heat forums"

I don't know if the noise will abate over time, unless you lower the water temp in the upstairs PEX zone & using longer heat sequences for the upstairs will help--you should be able to zone off the upstairs using a separate t-stat for the bedrooms, and a 3-way mixing valve that mixes cool water with boiler hot water without too much trouble:

Google "A little floor warming please"

by John Siegenthaler for his article & diagrams on how to zone off part of the house at reduced water temp; Google "the Glitch & the Fix" to view his excellent forum on these issues.

Another strategy widely used is to run the heating system at a lower temp (100-120 degrees) with constant circulation during the heating season using an outdoor reset (ODR); this tends to keep the water temp inside the PEX at a constant level & thus reduce expansion noise; since the smaller boiler circulators used now draw very little amperage, the electric expense is surprisingly low over the heating season.

Please post back to advise what your boiler temp reaches when the system is running, as well as if you have a split system of baseboard/radiators/radiant, or if everything's radiant throughout the house; also advise the model # of the circulator (pump) on the boiler, or if you have several small circulators for several zones in the house---usually, the smaller the pump the better in regards to noise reduction.

For example, if you've got one large powerful circulator on your boiler that's pumping out 180 degree water whenever the system calls for heat, you'll get a lot more noise than if the bedroom zone had its own dedicated small circulator that would GRADUALLY heat the PEX at a lower water velocity.

If you DO have such a single large circulator, try turning down the boiler water temp to 140 degrees to see if there is any improvement in noise reduction.

It might be a good idea to consult the Yellow Pages under "Heating Contractors" and have 1 or 2 experts who specialize in radiant take a look at the system; they should be able to steer you in the right direction at least expense.

Let us know of your progress & click onto my name & advise via a PM of anything you find as a remedy---
there is usually a way to skin this cat.

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