Between Joist Hydronic Heating

RLF

I'm building a new home and plan on installing hydronic heating between the joists in select areas of the home. The pex tubing will run through holes drilled in the engineered joist. Do I need to install grommets to prevent the wood from rubbing against the tubing? Is there a risk the integrety of the pex tubing will be reduced at the points it may rub against the wood as the tubing expands and contracts? I'm using heat transfer plates 12" from curves to hold the pex tubing to the underside of the floor. What is the best thing to use at the curves to hold the tubing to the underside of the floor?

Chris Maderia

Joist Heating/Transfer Plates

If your running 3/8" Pex which is recommended for joist heating your drill holes should be atleast 1 1/4" minimum. Seems like you are doing this 12" on center. Have you had a heatloss/radiant design done for you? I just designed a system identical to this application and my water temps were much to high at 12" on center(170 degrees). My floor R-Value was 1.4. What is your floor surface R-Value? You shouldn't need any clip at your bends and is you do use them they will most likely snap anyway.

hr

Some insulators I use

These drive into a 1-3/8" drilled hole, which is a common plumbing bit size. I use one size larger than the tube. ie. 3/4" for 1/2" tube. This allows the pex to squirm noise free.

If I have multiple runs, through a joist, I drill a 2-1/8" hole and run four tubes in the same hole. Cuts down on the number of holes and keeps all the tube grouped together.

I use the insulator with the ears for this and a zip screw to hold them in place. If I drill a bunch of joist in a row, I usually use the insulators in every other joist.

Generally TJI type joists will allow up to an 1-1/2" hole anywhere in the web, even at bearing points. For larger holes consult the hole drilling chart available from the lumber supplier. For dimensional lumber drilling, consult your local building code. They have hole drilling tables in them.

hot rod

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Duncan_2

Noise.

Personally, I sleeve EVERY pex-through-wood hole, using hangers like hot rod shows. If you're going though nominal lumber, a hanger on each side of the stud pretty much sleeves the entire tubing inside the drilled hole.

It's not just an integrity issue. PEX expands and contracts an inch per 10°F per hundred feet. As it expands and contracts during heating cycles, it can creak and moan like a ghost ship. Or snap crackle pop like Rice Crispies the size of basketballs.

If you sleeve the tubing properly, and give it room to expand and contract (use expansion loops on long runs), it will be the quietest, most comfortable system you've ever loved.

By the way... Kitec doesn't expand and contract as much as pex. And it's made in Canada.

Whose heat transfer plates are you using?