Installing Radiant PEX. . .Lessons Learned

[SmokeEater]

Plan to install single runs of 7/8" PEX between solid floor joists in older home. I mapped the runs all out, located the manifolds, counted number and size of holes to be drilled, and asked some friends over for a PEX party to help install after all the holes (1 1/2") were drilled. The joists were all rough lumber and about a full 2 1/4" thick. Many were doubled. Long story, but all help showed and the "expert" began to place the PEX. Suddenly, after his comments that had to do with alignment, I shrunk in a bit of embarrassment. Some of the holes were aligned because I used a template, but many were not. I did not know that the PEX could not withstand a sudden turn in any direction. The PEX had been stored in the boxes that it came in so the amount of flexibility was not known. My hard lesson taught me several things; have a real experienced installer check out the plan on site, ALIGN all the holes as best you can, keep the PEX warm, don't attempt to exceed the bending radius, and only invite your friends and neighbors when you are certain about the installation.

 

[Hunderliggur]

...and build your house with wood web trusses. We installed 5700 feet of 7/8" PEX with just one kink. Ditto everything else.

 

[huffdawg]

I felt your pain also. I installed 5/8" kitec for the second floor base board . That stuff doesn't like to bend very much. If I would of known the stuff was such a pain .


I would of predrilled all the second floor joists before I installed them. I had quite a few doubled for cantelever purposes . Boy! what a pain trying to drill those. trying fit drill into joist bays.

Huff.

 

[bpirger]

A good trick drilling in the bays, especially a double up version, is having a right angle drill and the spade bit extension rod....

 

[Frozen Canuck]

Radius bending tool...worth every penny. Ditto for a hole hawg for drilling joists....prob better for most members to rent that one.

One question, why such large diam tube for radiant staple up? Smaller tube is so much easier to work with. Yes you need more of it to deliver the load but the grief level goes way down. Frankly if I asked an HVAC pro here to use 7/8 tube for a underfloor radiant install he would likely tell me (exactly) where to stick that tubing. Now that would really be a pain.....

Hunderliggur hit the nail square on the head. If you plan to do radiant in a new build or addition use web trusses & avoid all the grief entirely. For that matter use them anytime you can......so much easier=less money, for the other trades if you do.

 

[SmokeEater]

Hunderliggur, don't I wish I had it as good as you. My old home was built before the truss joist. Though my newer garage does have them clear span for 28 feet. You could install 3" flex PEX in that thing. Envy.

 

[SmokeEater]

Bpirger, if I had to use a spade bit I would have put in radiant, it would have be baseboard or rads. I used the self feeding bits by Irwin, wicked good bit.

 

[SmokeEater]

Frozen Canuck, I'd be a Frozen New Yorker (live near Montreal) if I installed 1/2" PEX. That 7/8" is a current pain-in-the-u-know-what to install, but it will carry a lot of btus and that's what I'll need when the wind is at 30 knots and temps around -30. I have an old house, but it's well insulated and now it needs to be well heated. I agree that the 1/2" is much nicer and easier to work with, produces fewer curse words during the install, but.

 

[huffdawg]

Whats sort of heat tranfer plates are you using for this?

 

[heaterman]

7/8" ???

 

[DaveBP]

7/8†???

Well, I guess that I'm not the only one wondering...

Are we talking about 3/4" PEX called by its O.D. dimension?

 

[Hunderliggur]

7/8" PEX from The Radiant Company. Aluminium plates formed over the tubes, all of it stapled up, then a radiant barrier below that. For the second floor I have R13 Denim insulation (primarily for sound) below the radiant barrier above the drywall. 1" copper header to 7 300' loops for each of two zones. 3rd zone has 5 300' loops. For the 1st floor, the basement is open (100%) so it is just radiant for now. Eventually a drop ceiling with foil backed fiberglass ceiling panels.

 

[SmokeEater]

To answer Heaterman's and DaveBP's question, the PEX is 7/8" ID and is supplied by Radiantec at http://www.radiantec.com/index.php. They also supply the PEX to manifold adapters and preformed conduction plates.

 

[DaveBP]

So it's more like 1" PEX named for its ID.

No wonder you didn't think it was fun snaking it through holes in the joists. After running just a few 3/4" header feeds I can't imagine using 1". Congratulations on a battle hard won.

 

[Frozen Canuck]

So it's more like 1" PEX named for its ID.

No wonder you didn't think it was fun snaking it through holes in the joists. After running just a few 3/4" header feeds I can't imagine using 1". Congratulations on a battle hard won.

For sure that much pex of that diameter, woven through joist bays without a major kink fest is deserving of some sofa time, beverages included. No way I or any HVAC contractor here would even try. It would be back to pencil & paper time to find a way to meet those loads with smaller diam tube for sure. Congrats on still having hair left at the end of that project. Can't imagine even trying that on 24" O.C. joists, must have been an absolute nightmare getting those radius bends as you transitioned from one bay to another.

 

[SmokeEater]

Frozen, most of the transitions skipped a bay. Some were in adjacent bays, but not too many. To prevent from pulling too long a run through the same holes, we split the runs conveniently and I will splice with connectors later this week. The connectors are pricey -- $10 USD each. No runs were over 250'.

 

[SmokeEater]

You guys are right!! What a job, I'm plum still tired out from pulling and pushing that 7/8" PEX. We did put in 250' and did skip a bay, but that was more difficult than putting the PEX in the adjacent bays. It's too long a reach for a short armed guy or girl. All the other runs we put in adjacent bays. That stuff does not have a small bend radius. I also notice that near the manifolds, I'm going to have to use a heat gun or hair dryer to soften that big PEX up to bend it into the manifold ports. Just put 1 pair of them together today, the low temp radiant pair. I still have to put the high temp pair together. With info from the forum members, I decided to custom build the manifolds to fit right and save bucks. On a 6 port pair I figured I have about $220 in the 1 1/4" pair with a boiler drain, air vent, temp gauge, valves, and PEX fittings.