Tuesday, November 16, 2010

Pressure testing the radiant floor plumbing and discussion of pex tubing

When you work with this sort of tubing, the tools they make are very expensive.  With the expensive tools you can use the cheaper fittings  - a crimp coupling is about $1.  The tool to crimp is around a hundred dollars.  You can circumvent that by buying fittings that don't require crimping but each fitting, like the couplers pictured below -- are $6-9.  So the math is pretty simple:  if you're going to do just one radiant floor and don't plan on doing it ever again, just buy the more expensive fittings.  If you're going to do it in the future, invest in the tools.  I don't do this often enough to make purchasing the tools worthwhile. 

The other issue with radiant floor systems that isn't obvious is that there are two grades of tubing.  The least expensive tubing is what is used for water supply lines in mobile homes and other construction.  It's simply a plastic tube.  For burying in a slab they make a more-expensive tubing that has an additional coating on the outside of the tube.  The oxygen barrier pex tubing is usually 30-50% more expensive.

Here's a quote "The oxygen barrier, ethylene vinyl alcohol (EVOH), is applied to the PEX tubing during the extrusion process.  Typically used in hydronic radiant heating piping systems, the additional oxygen barrier layer is added to limit the amount of oxygen that can permeate into the system through the tubing, thus preventing rust from forming on any ferrous metal parts.  "

What this means is that if your heating system has metal parts in it that can rust the oxygen barrier tubing will retard that rust.  Functionally it's the same as the untreated stuff.  In this application I used the untreated tubing.   In this installation no metal parts are buried in the slab.   So if I do have a metal fitting that fails at some point in the future, I can cut it off and replace it in a few minutes.   If I were doing a system where I was burying metal couplings and stuff in the slab itself, I'd be inclined to use the treated tubing.   By using this cheaper tubing I've probably saved $300 between the higher tubing and tool cost. 

After installing the tubing and zip-tying it to the reinforcing mesh, it's important to test it.  It's pretty simple.  I've got two lengths of tubing here; so I install coupling and cap one end to make it a single tube. 
 On the other end I install a pressure gauge.  It's designed to allow you to pressurize the tubing, and after that you can look at the gauge to determine if there's any leaks.  I pressurized the tubing to 25lbs and left it overnight to make sure that everything was intact and good for the concrete pour. 
Left overnight, no loss of pressure.  We're good for the pour. 

Source of quote related to oxygen barrier pex tubing: 


Alexander said...

Good post, thanks for the info.

Anonymous said...

Ive installed a lot of heating and pots with pex. You really should have used the right stuff. It isnt just the fittings that are at issue but also parts in the heating units and valves and other areas. Closed loop issues. This is going to come back to bite you in the ass. Save a little now but you will regret it later in much higher costs.

Bruce King said...

Each pex loop is a single run of tubing. No valves or fittings in the slab. The pump may have some metal in it, and the water heater may, and those might fail, but if it does have a problem it's all stuff that is above the surface and accessible for repair or replacement. This is an experiment; if it fails, I'll update this post.

Anonymous said...

No it is the valves pumps and other metal that is outside the slab which is going to be suffering because you used the wrong type of pex. Yes you can repair it but it is going to cost a lot of money. Too bad you already poured. I hope you pulled up the wires so they are not sitting at the bottom of the slab. Failure to do that is a common error and something many contractors dont bother with. Walking all over the wires makes it worse.

Bruce King said...

Ya, we pulled up the mesh to center it in the slab. You can't see it, but there were wire loops tied in every 4 feet or so so that you could lift it after the scree had passed, and then clipped off a little under the surface after that.

I appreciate the input, and if other folks are putting in floors there's now reasoning for them to use the more-expensive tubing. I think you bring up a good point. For me, if it turns out to be too much trouble I'll just stop using it and just have a slab, and be out 1 day of my labor and a few hundred bucks. low cost experiement.

Plumbing said...

PEX tubings are the best pipes and tubes that you can possibly find. These tubes can withstand time and weather and be of use to you until you have 2 generations of grandchildren! That is, if cared for properly.