PEX advice

[sands35]

So, getting ready to install PEX for detached garage radiant floor. 26x32 footprint on the structure.

Since things are moving fast, I needed to buy 250' rolls of PEX rather then order 300' rolls. Oh well.

Anyway, I have 4 loops at 170, 169, 167 and 163 (at least on graph paper). The 163 loop services the area in front of the garage door so that might work out better.

Sorry, not at a place where I can scan in the drawing yet. Perhaps later today.

I'll be doing the install on the 8th and 9th. Concrete pour is the 10th.

Question - is the ~5% difference in loop length OK? (I plan on laying out the pex and likely will need to tweek it a bit to get is closer to even loops)

Planning on vapor barrier then 2" XEPS foam. Pex stapled to the foam then wire mesh. GC recommended the mesh on top of the pex to hold it down during the poor.

 

[rburke65]

5% will be fine....in my opinion.

 

[matouse3]

up to 10%, from what I have researched, is considered acceptable.

I would "suggest" to the GC that he put the mesh on chairs to ensure even height of the mesh and protect against accidentally pulling up the pex when they try to pull up the mesh.

There should be no issues with the pex rising if its stapled to the foam.

 

[Highbeam]

Your pipe lengths are fine. Head loss will be lower with the shorter runs.

Here's the problem, you don't have enough pex. 832 SF building and only 669 LF of pex means you aren't holding the 12" spacing. You could fit a whole additional 170 foot loop in there somewhere.

On the mesh, laying on the pex is perfect. The bottom 1/3 of the slab is where you want the mesh since that's where the tension is. The PEX won't float after being attached to the foam. The mesh won't need chairs because it will be held up by all the PEX.

Your method sounds great.

 

[jlckmj]

I have a 24 x 32 and I used 4 loops between 210 foot and 230 foot and I have no issues with flow, it seems to work well.

If nothing else, run it a little closer together around the outside edge to help combat heat loss (or cold infiltration) from the sides.
Jim

 

[matouse3]

On the mesh, laying on the pex is perfect. The bottom 1/3 of the slab is where you want the mesh since that's where the tension is. The PEX won't float after being attached to the foam. The mesh won't need chairs because it will be held up by all the PEX.

Your method sounds great.

Shouldn't the mesh be closer to the middle of the slab? Setting on the Pex it will only be +/- 1/2 inch from the bottom- or am I missing something?

I guess I'm assuming 1/2 inch pex and 4" slab.

 

[sands35]

I may add in a few extra loops and see what happens on the layout. I have a few days to think it over.

It's 26x32 on the outside, so effectively the slab is 25x31. I can fit one more loop in there, so need to think about it.

 

[Highbeam]

Shouldn't the mesh be closer to the middle of the slab? Setting on the Pex it will only be +/- 1/2 inch from the bottom- or am I missing something?

I guess I'm assuming 1/2 inch pex and 4" slab.

So concrete is great in compression, poor in tension. When you load a slab, or beam, the top 1/3 is in compression, the middle 1/3 neutral, and the bottom 1/3 is in tension. The reason we add steel to the concrete is to help it with tension. As such, you want the steel in the bottom 1/3. Really, lower the better so long as it is in the mud well enough to get a grip.

Once the slab totally cracks through, the steel in the middle should help prevent the two sides of the crack from separating vertically or horizontally. Steel in the bottom 1/3 will do that too.

 

[matouse3]

you want the steel in the bottom 1/3. Really, lower the better so long as it is in the mud well enough to get a grip.

Do you think laying the mesh on the 1/2" pex at the bottom 1/4 of the slab will be surrounded by enough mud to get a grip?

 

[matouse3]

Sands- did you have a chance to get a copy of your diagram scanned yet?

You're probably all in on the install today since its the 8th?

 

[Highbeam]

Do you think laying the mesh on the 1/2" pex at the bottom 1/4 of the slab will be surrounded by enough mud to get a grip?

Better than most. Most mesh sits on the bottom of the pour, I'm as guilty of this as the next guy. If you actually get a full 1/2" emedment then I do believe you will be in great shape.

 

[Mr onetwo]

I may add in a few extra loops and see what happens on the layout. I have a few days to think it over.

It's 26x32 on the outside, so effectively the slab is 25x31. I can fit one more loop in there, so need to think about it.

You will be sorry if you don't add another loop! Pex is cheap...in my experience you can never have too much within reason.You should also should think long and hard about putting in rebar on 12" centers....mesh is a total waste of money!

 

[sands35]

Version 452....

The garage door is at the bottom where the numbers are. Not happy with loop #1 (left hand blue loop). I'll likely take out a loop at the bottom to get a proper loop on the left and add a foot or two to all the other loops. Those zig zags aren't going to work. (frankly, I just ran out of time yesterday to play with it).

The man door is at the top left so the door will swing in front of the wall panel. Wasted space anyway, so might as well use the wall for something useful. For what it's worth, the electrical panel will be at the bottom right (closest corner to the power pole).

The blue square at the bottom left is where an air compressor will go, bolted to the floor. The two dots in the middle is where the bases for a lift will go. I recessed two 4'x4' pieces of 2" extruded poly foam board down another 2" for a total of 6" of concrete in that area. I'll pinch the loops around that to avoid the columns.

 

[sands35]

Version 521....

Cleaned up the left hand loop.

Also, the working floor area is really 30.5 x 24.5, though the outside is 32x26. So the loops will be pinched a bit more than shown on the width.

There is enough fudge that I'll be able to get the loops pretty close during the layout.

 

[matouse3]

Version 521....

Cleaned up the left hand loop.

Also, the working floor area is really 30.5 x 24.5, though the outside is 32x26. So the loops will be pinched a bit more than shown on the width.

There is enough fudge that I'll be able to get the loops pretty close during the layout.

Looks close enough. I'm glad you ditched that wiggle line along the left hand side you had in the previous version- you would have had fits trying to pull that off.

 

[Highbeam]

Any reason that you didn't just run the loops all the way top to bottom and then back home? That whole separate bottom loop could be avoided.

I suppose it doesn't really matter. That's the great thing about these floors. So long as your spacing is right and your loop lengths are close, you are allowed to be creative.

 

[sands35]

Mostly because the panel is not in the middle. Also I wanted a hot loop at higher density running to the garage door area. I'll only do the PEX layout once, but if I put the panel where I don't want it (just to make the tube layout simpler), I'll have to live with that for 20 years.

Loop 4 has 6 passes and a small loop, loop 3 has 8 passes and no extra loop, loop 2 has 8 passes and an extra loop - basically to balance the difference in run from the panel. Conceptually, loop 4 and loop 1 are more or less the same, just turned 90*

I'd rather have done 3 loops, but needed to get the PEX fast and they only have 250 ft coils, not 300 ft coils at Menards.

 

[sands35]

Pex is in. Held 80 PSI for an hour with no issues. Checked it this morning and it was 75 psi, mostly because the temperature dropped 30*F overnight.

The pour was scheduled for today, but we had rain last night and this morning, so it will be Monday.

Pex lines are within ~2 feet of each other. At least what I ended up with at the end (assuming that the 4 coils of PEX started out at the same length...). I did have to tweak two of the loops (both ~6ft too long), but there was enough slack in the layout that it didn't present a problem. Loops a little closer here, a little further there.

I ended up building a quick and dirty board to hold the end of the lines and support them for the pour. I used 3/4" NM electrical conduit elbows for the entry into the slab.

 

[darkk]

When I did my new addition with PEX, It held 120lbs air pressure for 3 weeks. As far as a 5% difference in you layout, I wouldn't worry, you can also up the flow rate with your circulation pumps or increase the feed water temperature a little to compensate if necessary.

 

[TheEquineFencer]

I bought 1000ft rolls when I did mine and put it 6 inches OC. 320 ft max run, all were well below this. I also put 100 PSI for 48 hours and kept it there when doing the pour and for 4 days past. I used PVC over the PEX at the joint cuts.

 

[sands35]

It took me three days to figure out that all i needed to do was dunk the manifold and fittings into a bucket of water to see if they leaked air. (I left the lines ~4 feet long out of the slab). Sure enough, my fill and pressure gauge manifold had a leak. I've been doing home DIY projects for years and I'm still surprised at how much torque it takes to seat an NPT fitting. It's held 80 psi since last Friday.

 

[Highbeam]

Especially a crappy foreign made NPT fitting.

 

[TheEquineFencer]

It only took me two days to keep everything from leaking. I'd check it around 5 am, start tracing the leak, find it and start again at 5pm, then 11pm. they were minute leaks, proably would never leak water, but I felt better when they quit.

 

[wildlife]

Especially a crappy foreign made NPT fitting.

highbeam and others,

what are the better fittings to use?
i will only have a handful and might as well order the better ones?
thanks,
wildlife

 

[TheEquineFencer]

highbeam and others,

what are the better fittings to use?
i will only have a handful and might as well order the better ones?
thanks,
wildlife

Most of my leaks were self inflicted. I didn't use quailty, or enough Teflon tape or any pipe dope at my connectons to start with...

 

[Highbeam]

The folks that do lots of plumbing have grown particularly unfond of the now common chinese black iron fittings. Porous castings, and pinholes are the common complaint.

Apparently, in the olden days the US was better at making them.