PEX stapling - Floor or Joist?

Tom Rothe

Pex tubing – Attach directly to the floor, or to the joists, or zip tie to hangars that span the joists????? I need to finish and possibly improve on the job that my heating contractor did. I’ve gotten conflicting advice. Our home is a 52-year-old remodel that water heat was the only solution. The original house is concrete block on the first floor, 2 X 4 second floor construction. An addition is 2 X 6 construction and concrete slab where a garage was. This leaves very different heating requirements and our seven zone system should work. The second floor has baseboard radiators. The boiler is set at 160 degrees with a mixing valve to cool the water to the pex areas. There is only one pump. The pex areas end up with between 120 and 160-degree water. The area that I need to finish up yet is the first floor. It has a ¾ inch pine board underlayment laid diagonally. The finish layer is ¾ inch maple “original” hardwood flooring over 75 % of the area, with tile over concrete board in the kitchen and entry areas. The contractor stapled the pex tubing to the floor with one-inch staples. The floor is noisy, but that is not my biggest concern. The noise is of coarse from the pipes moving as they heat. I am concerned that this movement will eventually cause the tightly stapled metal staples to wear through the pipe as it shifts. The staples are easy to pull out. Replacing them and moving the pex to the joists would be easy. I would reattach with ¾ inch plastic wiring ties or the official PEX talon clips. We did not use the metal heat dispersion plates (that most web sites seam to recommend) because there are numerous nails coming thru the underlayment wood from the hardwood floor. I suppose we could bend all the nails over, if the plates are the far better way to go. However, I have seen some references out there that heating a “pocket” of air under the floor is better anyway. A disadvantage of this is that the system needs to be run a higher temperature, which is happening here anyway. No matter what we do, I intend to place the Reflectix (aluminum foil and air-bubble) insulation below the PEX tubing. In my hunt for the right solution this website was mentioned as “the” place to go. HELP!

Perplexed homeowner needs experienced professional advice.

Tom Rothe
920-235-6789 Work
920-426-2090 Home
tomrothe505@yahoo.com

kevin coppinger_4

Tom....

where are you? And more important where is your contractor!Was there a heat loss done? If there are nails , plates will help at least the wirsbo joist trac extruded plates will help. You need to keep even pipe layout lest you get stripping. What size tube? We need a lot more info...it might be better to get your contactor back or get another heating contractor out to where you are...kpc

Mark Eatherton1

He's in Oshkosh,

b'Gosh!

ME

hr

It's not to late

to do a heat loss and design. Only then will you know how many btus per square foot you need to heat the space.

I'd keep an eye out for those rooms with 3/4" sub floor and 3/4" finish. That 1-1/2" thickness will take some energy to penetrate. That combo is a 1.8 r value for your calcs.

By far conduction (transfer plates) is the most powerful way to get the heat to the space. If at all possible I'd go with transfer plates.

Hate to see you go to the trouble of a redo and still not meet the load on desidn, or below, days

I'm not a big fan of stapleling pex directly to the sub floor. As you noted the expansion of the pex creates a lot of wear points!

hot rod

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Mark Wolff

True staple-up

I only do staple up style. To me the underfloor convectors are a marketing gimmick and a waste of money.

Stapling tubing to the underside of plywood with metal staples though is NOT true staple up. First you should at least use plastic coated staples (like the manufacturer provides and recommends!) OR you can use 2 hole suspension clamps to allow more movement and eliminate expansion noise. The 2" air space is vital to allow the heated air to warm the whole surface area of the floor, not just right above the tubing. Otherwise you will feel hot and cold spots on the floor above.

Pull all the metal staples and start over with the right fastening system. Don't zip tie it to the roll block bars. Besides the tubing is supposed to be supported at a MAXIMUM interval of 32". Hope all this helps.

Floyd_5

It depends.....

What do you want... a nice even heat or stripping... if you put he tubing on the joists you will get malor stripping...put in on the floor and it will be better....add plates and you can lower your water temps. and get even better more even heat.....you'll get out of it what yur willing to invest in it!
First off though you better have an accurate heat loss done and see if you can even get enough heat out of the staple up to meet your demands and THEN decide what type of system you need to install.

Alos, you said another thing that concerns me... you said that you have 1 pump and a mixing valve in the system.....if you have a three way thermstatic mixing valve and only one pump then you have a major piping problem right off the bat.... there is no way that you can make that system work right. Check it out!

Just my 2c worth

Floyd

Dak

true staple up

Mark,
You said a 2" airspace is vital to allow the air to heat. So what would you put under the tubes.......metal transfer plates, reflective bubble foil......both, or something else?
thanks.

Mark Wolff

Nothing

The tubes are attached to the underside of the plywood on the floor. There is a 2" airgap that they sit in to allow free air movement. In the rest of the floor joist space is batt insulation. The most R-value you can fit in the remaining space. Under that is the drywall lid for the room below. If below is a suspended ceiling, put sheetrock up anyways. You want to stop the heat from being driven downward by the solid mass of plywood above it.

As for not enough btu's out of plain tubing, get real. Up until recently (when the plate craze wound up) that was all that was available other than slab style. If you run your tubing on 8" centers (down and back in each joist bay) you should NEVER have problems with too little btu output. Double check your heat loss calculations to be on the safe side, but I have never needed more and I'm in cold country (Alaska).

Mark Wolff

?

I have never heard of people attaching tubing to the actual floor joist. Does that happen much in your area? What kind of logic is used to justify it?

Wayco Wayne_2

I've done staple up

and plates. Plates are the safest way to get the heat you need. They inject the heat directly into the sub-floor. I have used a hand grinder to remove all of the nail points from hardwood. I have also used staple up using talons to attach the PEX to the sides of the joists. Works fine and brings the PEX down where nails can't reach it. I know use Wirsbo Pex clips. They work even better. Something new I'm doing is installing a product called Thermopan to create the 2 inch air space. It's a board made of cardboard with foil on one side that is used by some HVAC contractors to make return air passages out of floor joists. It comes in 16 and 24 inch widths, with bend down wings that are used to staple it to the joists. I have heard it makes for a nice definite air space so the insulators can push the insulation up against it and not have to worry about leaving the 2 inch air space. I've seen insulators eyes glaze over as I tell them of the 2 inch air space requirement and have had to take the time to follow them up and correct any short-comings. This product sounds like it will give me piece of mind. It also has a foil face that will help heating initially, but as with any foil product it's reflectability will be compromised with the years as dust builds up and covers the foil. Hope this helps. WW

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hr

Confusing terms

Staple up means the tube is STAPLED to the bottom of the subfloor, in direct contact with, for some conduction transfer. It started with the rubber tube manufactures, solar roll, Heatway. It is a method best used with rubber as the tube movement is not a concern. Of course rubber is an insulator, and transfer through the wall is a concern.

Next would be Suspended tube or Joist bay heating. Here the tube is suspended below the subfloor. There is no conductive transfer! Clips brackets, coated staples are all attachment methods. I fasten the tube to the sides of the joist with Sioux Chief fullcir circle clamps. A 2" space is good for the insulation position. Rim joist insulation detail is CRITICAL.

Next would be transfer plates. By far the best way to transfer the energy to the floor, in a below floor application. Conduction transfer is by far the strongest and allows lowest supply temperatures. Also eliminates noise issues, when quality extruded plates are used!

There are a number of studies that show the output and limitations of the various methods.

Perhaps the KSU/ ASHRAE/ RPA study is one to look at as it was not done by a manufacture

Siggy has done plenty of research and FEA modeling of the various methods, also.

The RPA has infared video and stills of the three methods also to show the difference in actual operation.

Pick the method that suits your application and BTU load requirements. Ther is a big difference in the three methods!

hot rod

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Dak

batt insulation under pex

Mark Wolff,
Thanks for answering that question I haven't heard of using just the insulation under the tubes and nothing else.
Let me just ask one more detail to that answer..... when you apply the bat insulation do you apply it with any of the paper vapor barrier on it that comes on it or do you apply it without the paper? If you do leave that paper barrier on the insulation does the paper side go toward the tubes or the other way around?
thanks.