PEX-AL-PEX vs oxygen barrier PEX

mtliving

I'm seeing conflicting information on this. I'm planning an above subfloor install with plywood sleepers and aluminum fins.

The main benefits of PEX-AL-PEX seem to be decreased/minimal expansion noise and ease of installation… but I'm seeing horror stories of about delamination and leaking.

On the other hand, oxygen barrier PEX can be louder but seems to be more stable over time. Would using silicone in the aluminum fin channels eliminate the expansion noise?

As an owner-builder who doesn't do this professionally I'm having a hard time knowing which to choose and would welcome any input folks have who have been down this road before.

Thanks!

hot_rod

Properly installed either tube will be 100% noise free. For a first time DIYer, PAP is trickier to work with and you may end up with a lot of repair couplings! The PAP that is still available has been around for many years now, and well proven.

In theory PAP should be a 100% O2 barrier, where standard pex allows a % of O2 ingress based on operating temperature, the DIN 4726 standard.

The easiest tube to use is a 3/8" "A" type pex. Very flexible easy to heat kinks out of. Loops would be limited to 200- 225'.

Noisy plates come from, the tube moving in the plate, usually that will be squeaking noise. I'm not convinced silicone adheres to pex very well. But any other adhesive would need to be approved by the manufacturer. Water based foamboard adhesive seems to be fairly benign, and it sticks to plastics better.

The plate expanding and contracting, sometimes called oil canning. The thin flashing thickness plates are prone to this noise, a click, click, click every time the circulator starts sending the heated water out..

A tap noise could be where the tube rises up and touches the flooring, not properly fastened loop ends, for example.

Yet another option is sleepers with concrete or gyp poured over the tube. The tube will not move and it adds some mass. We called it a medium mass system, between a slab and a dry system.

This was the system we used when the customer wanted a nail down hardwood over radiant.

Depending on the square footage you can mix gypcrete onsite.

Gyp, sand and water basically. If you go this route you need a lot of staples as the gyp will float the tube up. Like every 12"! I have other tips for gyp pours from making all the mistakes 😳

Noise issues, as well as comfort can be helped by ODR or an actual constant circulation piping arrangement. The less the temperature swing the better radiant feels and less it talks to you.

mtliving

Thanks for your input and detailed reply Bob. I'm going to try to get my hands on some 1/2" PAP to see what it feels like. Repair couplings sounds like a nightmare! Side note - I'm now working through some of your Shop Talk content and I'm finding it very thorough and helpful - thank you.

Kaos

Regular barrier pex works just fine and much easier to run. Make sure the pipe has a PE layer over the oxygen barrier, the ones without PE layer are near impossible to install noise free.

Pex Al Pex is good for an install where you need to form the tube to stay in a certain shape like snow melt under stairs.

RascalOrnery

for me the standard oxygen barrier was like trying to wrestle a snake. Probably took four hours or more to pipe a room due to cross bracing between joists and wiring being in the way.

AlaskaDick

I'm just a home owner installing my own underfloor staple up-using thin heat transfer plates, but my 70+ years working with mechanical things has given me some familiarity with heat transfer and sliding surfaces.

I have to agree with Hotrod's belief that silicone doesn't stick to PEX very well. (I've been using silicone for better heat transfer on 250' of C groove plates given to me by my neighbor. The plates I bought are omega groove which contacts the PEX much better and I won't be using silicone on them.) Silicone is also elastic, so it's unlikely that there is a mechanical reason that using silicone could significantly control the expansion of the PEX. I can think of three other reasons silicone adhesive would decrease noise as the temperature changes.

• Silicone improves heat transfer from tubing to the plates, so the temperature difference would be less, decreasing the difference in expansion between the two as temperatures change.
• The silicone would tend to dampen noises from the thin aluminum plates.
• A thin layer of flexible silicone between the two surfaces would avoid a direct PEX to aluminum sliding surface and decrease the stick-slip phenomenon which I suggest is the likely source of most of the noise. (Some noise may also come from oil canning and the expansion of the plate against the subfloor.)

hot_rod

The whole design concept behind the ThermoFin brand was the thicker aluminum in the groove channel and the plate itself.

Of course aluminum is $$, sold by the pound. So the heavier plates will tend to be more expensive.

The thin flashing gauge really need to be pinched between two wood layers to keep them quiet.

The "king" of heat transfer is copper tube in ThermoFin😀

Kaos

The best way to reduce noise, no matter the setup is to run a good outdoor reset. If the loop temperature doesn't change much, there is no thermal expansion and no noise.