Attaching 1/2\" hePEX Plus for slab heating???

Gasper

jUST THOUGHT I could save when I don't need the whole thing warm.

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Gasper

I'm installing 1/2" hePEX Plus in a 35' X 29' garage floor. I thought I'd put in 4-250' loops in. Also thinking about 2 zones. What do you guys think? (I also had an earlier post on slab insulation.) The cement guys have the wire mesh laying out on my lawn. It's not the beefiest stuff. Will I have a problem keeping the tubing and the wire mesh in place during (or even before) the pour? We're figuring a 6" slab, with saw cuts. So we obviously have to keep the tube down a couple of inches. Any good suggestions on this? Yes I am a licensed/insured/etc. mech./boiler contractor. Just not a lot of infloor experience (mostly due to my location....steam heat, old homes, etc). Thanks Again!

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hr

Wow, why a 6\" slab?

19 yards of concrete! Seems like a bit of overkill unless you work on heavy machinery

hot rod

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Gasper

Saw cut clearance?

Is the 6" going to kill me on fuel bills trying to heat it? The cement guy just figured to have plenty of clearance for his cuts. I figured more is better!???? The garage will be mostly empty for the next four or so years (indoor basketball, etc). After that I'm not sure, probably morph int a regular garage, cars, etc, maybe some of my business equipment (I'm hoping to avoid the last one.

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Unknown

4", staple the tubing to the foam, lay mesh over that. Fastest and easiest install.

All going to 6" does is make your lead/lag issues larger, it won't effect the long term fuel bills (though that initial startup is going to drain some serious fuel!).

Gasper

Tubing in the middle?

That would put the tubing at the bottom of the slab.....no problem, or inefficiency?

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Unknown

No problem, slightly longer reaction time and very slightly higher water temps... concrete doesn't pose a lot of resistance to heat transfer.

Gasper

Ok thanks but what if......

it was your garage and you wanted the best? You mentioned that attaching to the insulation was fastest and easiest. It is my own residence so I'm willing to put in the extra time, effort, and cost to do it the very best (withen reason I guess). So is there a better way to install for the long term comfort, response time, effeciency, etc? Thanks

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Unknown

I understand, and I am not one to cut corners if there is a significant difference.

I would personally staple to foam and control it properly so response time is basically a non-issue. response time is going to be an issue no matter where the tubing is, that will need to be addressed by proper control and usage.

That said, you are technically ever so slightly superior with middle of the slab tubing, but so slightly I would give it no thought whatsoever. Personally, if the choice were between a 6" slab with tubing in the middle and a 4" slab with tubing at the bottom, I would consider the 4" slab superior due to the lesser lead/lag issues unless you are trying to store heat for some reason (off peak electric rates, solar storage, etc), in which case the additional mass is useful.

Gasper

Thanks Rob

Sounds good to me. I'll save on the concrete costs also. And with the tubes at the bottom I guess I'll be fine with cement guy saw cutting for his joints. I do already have the foil bubble wrap, can this be used with the foam? Or should I just return it? Thanks

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Unknown

It's a pretty expensive vapor barrier. I'd take it back and get some 6mil poly.

Edit: and educate the supply house guy while you're there.

Paul Pollets

Foam Clips

I've found that the mason's trip over the tubing and break off the foam clips during the pour.

I'd use a 4" pour, with R10 under the slab and 6x6" welded wire mesh to tie the tubing to. We have the mason order the 6x6 mesh in flat pieces, rather than rolls, so it stays flat. Sometimes we stake the mesh thru the foam to make it secure. We tie the tubing every 18" with 5" nylon ties. The welded wire mesh should be overlapped and secured as each pice is set.

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hr

Same here

foam insulation, 6X6 mesh in sheets if possible, and wire (bar ties) to the mesh. Foam staples are more money and tend to pop out, especially on the loop ends.

The difference between a 6 and 4" pour is about 7 yards. possible 700 bucks or more depending on your local yard cost.

Also 19 yards would be 76,000 lbs of concrete to warm up. 12 yards would be 48,000 lbs. A bit less btus and time to ramp up less mass.

Typically they cut 1/3 the depth of the slab. A 1", or so cut should not reach tube at the bottom of a 4" pour.

If you lift the mesh and tube to center it in the slab, skip the saw cuts, from my experience, as you run a good chance of hitting the tube when it floats.

hot rod

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Gasper

Ok then........

lots of good ideas I have to sort through. I'm thinking 2" Owens Corning Foamular 250 over a good plastic vapor barrier. Then foam clips, dealing with a few broken here and there (I'm guessing the price for the clips one job will be ok, the rep will loan me the tool to set them). Then placing the flat mesh on top of thee tubing. Then watching the heck out of the cement guys. I'm assuming that they will be pressing on the mesh that presses on the tubing. How is it possible for cement guys not step on the tubing even by accident? I do think saw cuts are desirable......but then again I'm not a mason. I know the cement guys pretty well, so I know they will give me the best they can. Then 4-250' loops of 1/2" hePex Plus, with two zones. This isn't the space shuttle but what do you think?

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Unknown

Not a big deal if they step on it.

Why two zones?

hr

The concept of the foam clips

is to do away with the mesh. Really all the mesh does ishold the tube down.

If you use the foam clips or staples, skip the mesh altogether and use #5 rebar on a two foot grid over the pex.

This does several things for you. The bar holds the pex down well should the clips pop out. The rebar adds strength and integerity to the slab. The pex by default holds the rebar up into the pour where it does the most good. And it gets away from the crummy roll mesh which adds little or nothing to the slab strength and poses a trip hazard. Rebar will handle any shifting in the slab should it ever crack, also.

hot rod

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Gasper

Two zones because...

I just figured if I'm working in there on a vehicle or whatever I could save some gas and $ by just heating half. Is this a dumb idea?

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Gasper

The mesh is already onsite...

not a big deal though. They can always use the stuff on the next job. But it is te flat stuff (4'X 8' squares?), not in a roll. But no it isn't re-bar thickness/size.

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Unknown

Is this two rooms? If not, it won't work.

Also, if you are not planning on leaving it half unheated for, oh, about a week at a time, it's not worth turning it down. Slab and setback are not friends. Continuous, low level heating is the name of the game.

Unknown

Nope, you'll never get a real temperature differential, you'll just be making half the floor work twice as hard to maintain the room temp you have dialed in.

hr

but you could

manually shut off two zones and that floor slab area will cool, while the active loop area will keep that slab area warm. Somewhat like a zoned snowmelt

Yes the whole space will still warm as heat goes to cold unless you wall off the two rooms, and at design day the two loops running would probably not meet the load, or satisify the t-stat temperature.

hot rod

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Unknown

But your heat will bleed from the heated side to the unheated side. The end result will be a couple of degrees in difference between room temps on both sides, except half of the slab will be working twice as hard to maintain the room temp it's told it needs to maintain. You're either raising the water temps to meet most of the load with half the tubing, or you're dropping the room temp on the heated side due to excessive "loss" to the unheated side. Pick your poison.

Gasper

What if I use 2 t-stats?

Down the road I may wall a secrion off.

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Unknown

Loop it seperately, add zoning later if you want to.

johnnyd

shutting down half your loops

If you're in a really cold climate that is also subject to sudden cold snaps, be mindful that if you mess with setback and keeping 1/2 of your loops shut down, you could freeze that 1/2. Ask me how I know.

Also I would vote for the 2" rigid over 6 mil poly, tubes stapled, rebar on 2' centers, 4" concrete, seal coat, saw cuts.

Gasper

Glycol? 5\"?

I'm planning on some type of anti freeze. I plan on shutting it down completly from time to time. That should be ok right?

The cement guy prefers 1" deep cuts. Has me a bit worried since I am going to tie to the flat mesh, and we were going to just pull it up a little bit when we pour. Being careful, shouldn't I be ok with the flat mesh? Will the extra 5" really cost me that much more in fuel costs?

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Gasper

Wall stat or in-slab sensor prefered?

What do you think? Thanks

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Unknown

In slab sensor in addition to a wall stat ONLY if you need to maintain a minimum slab temp (areas that get solar gain and shut down, needing to ramp up later, or low load conditions perhaps), or limit a max temp for wood floors.

In your case, wall stat only, though I would use a nice PWM stat like the Tekmar 508, gives better control and better action.

Gasper

Thanks



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