Tubing installation question

[Evilcactuar]

Hey guys, I 'm doing a 6" slab with 1/2" pex, on 2.5" of rigid foam. I was planning to staple the pex to the foam, but my contractor is giving me serious kickback and insisting that it should be tied to the wire mesh halfway up the slab. He's also telling me that they should do shallow cuts to accommodate it (like under an inch), and the slab will take forever to warm up with the pex at the bottom. Am I nuts? I don't feel like it's going to make much difference, as the heat is going to radiate both directions, and its not really an instant on solution anyway. If the end result is the same I feel foolish digging in my heels, but I feel like putting it at the bottom of the slab eliminates any chance of them puncturing it during the pour, and they can do 2" cuts.

 

[beatuptruck]

I'm getting ready to pour a 5" slab. My plan is the same as yours, staple the pex directly to 2" foam. My research sugested that having the pex at the bottom of the concrete may make the hydronic heat slower to react to adjustments in temperature. I'm doing rebar on chairs ontop of the pex. If you're planning on using mesh anyway it might also be easier/cheaper to zip tie the pex to the mesh? Will the mesh be properly supported or "pulled up" while concrete is poured? Is your contractor a plumber or a concrete contractor?

 

[Evilcactuar]

The guy I was talking with is a GC, there's a concrete sub coming in for the pour, but the GC would be doing the site prep. I'm willing to put down the pex myself, I'm not really worried about the time, more the end result.
I'm going to make them do chairs.

 

[yeldogt]

I normally do the mesh -- just so I can keep the PEX uniform as I lay it out --- I'm OCD and can see it down there after the pour.

It's all about heat transfer. More tubing = faster response. Most important: more tubing = lower water temp.

If the tubing is near the surface it stands to reason that when you first turn on the floor-- as the heat radiates out the top will see heat faster ..... but, you must get the whole slab up to temp eventually. Slab radiant is all about constant circulation .. lowest possible water temp always going around in the floor. IMO -- the tubing is fine lower .... but 6" is a lot of mass.

I do a good plastic sheet -- proper foam insulation and as I said above I like the mesh as I always do some type of sub zoning within the project. I never just run the PEX back and forth. I also never go above 8" apart.

Why are you doing a 6" slab ? Make sure you used enough tubing and don't have long runs

 

[Evilcactuar]

The plan is 12" spacing 1/2" pex, i'm going to do a 2 post lift and a 4 post lift, and I'm always buying something heavy (like a diesel skid steer), so I thought 6" would be good at 4000psi. I'm not looking for the shop to ever be "warm", i'll be pretty content at 50 degrees in the winter. This business where I lay in some ice and my pants freeze to the ground again is for the birds. I have it laid out to 7 235-265 ft loops. (1800 sq ft building). The loops are laid out to circle around the perimeter and work inwards, and I planned to alternate the direction. I also don't plan to shut it off all winter after its turned on, so i'm not really concerned about the speed to warm up. My understanding was that the thermal mass of the slab will reheat the building quickly after you open and close a door, obviously it will use some energy, but I don't think the overall comfort of the room takes a big hit, like if it was blown air.

 

[Evilcactuar]

obviously not running any pex under the 2 post, but I was planning under the 4 post (since I'm not sure where i'll be putting it, and don't have any plans to bolt it down)

 

[Sawlog]

We always use 6in wire mesh to tie the apex down to. It helps to keep things nice and straight. Take a ton of pictures when your done with a tape measure stretched out. I just had to look up pictures from a job we did 15 years ago because a guy was wanting to add some walls in his basement. Holes in apex can be fixed but who wants a radiant system with a coupling in the floor.

 

[Evilcactuar]

That's a great point

 

[stingry]

Try not to overthink this. A radiant floor is very forgiving. I have 3600 sq ft of 5” concrete. I stapled the pex to 2” XPS with mesh laid over the top. I tried to maintain 12” spacing but it wasn’t uniform and varied in spacing in spots. I have two zones controlled by eye level air temp thermometers. I keep the air temperature at 65 degrees all winter. This will be my 3 rd season and couldn’t be more pleased with the results. There are no cold or hot spots in the building and the floor surface temperature is constant over the entire floor. The most amazing thing to me is the fact that I can open an overhead door and when closed I can stand by it and immediately feel warm because of heat radiating from the floor.
I installed the XPS and pex myself. Definitely a two person job but not that difficult.

 

[yeldogt]

Try not to overthink this. A radiant floor is very forgiving. I have 3600 sq ft of 5” concrete. I stapled the pex to 2” XPS with mesh laid over the top. I tried to maintain 12” spacing but it wasn’t uniform and varied in spacing in spots. I have two zones controlled by eye level air temp thermometers. I keep the air temperature at 65 degrees all winter. This will be my 3 rd season and couldn’t be more pleased with the results. There are no cold or hot spots in the building and the floor surface temperature is constant over the entire floor. The most amazing thing to me is the fact that I can open an overhead door and when closed I can stand by it and immediately feel warm because of heat radiating from the floor.
I installed the XPS and pex myself. Definitely a two person job but not that difficult.

You are not heating the air -- it's like standing by a fire outside.

 

[yeldogt]

The plan is 12" spacing 1/2" pex, i'm going to do a 2 post lift and a 4 post lift, and I'm always buying something heavy (like a diesel skid steer), so I thought 6" would be good at 4000psi. I'm not looking for the shop to ever be "warm", i'll be pretty content at 50 degrees in the winter. This business where I lay in some ice and my pants freeze to the ground again is for the birds. I have it laid out to 7 235-265 ft loops. (1800 sq ft building). The loops are laid out to circle around the perimeter and work inwards, and I planned to alternate the direction. I also don't plan to shut it off all winter after its turned on, so i'm not really concerned about the speed to warm up. My understanding was that the thermal mass of the slab will reheat the building quickly after you open and close a door, obviously it will use some energy, but I don't think the overall comfort of the room takes a big hit, like if it was blown air.

You want to think about the water in the tube -- it starts out hot and gets cold as it goes around. The problem with a very cold slab --- is the delta T (temp going in vs Temp coming out) is large.

You want to have the hotter water near areas where it will need more BTU's -- or you want it to be hotter. The nice thing about radiant is you can control the temps with the tubing ... A part of the shop where you can be all the time can done with twin tubing.

Radiant is forgiving --- but, doing it correctly will give you max comfort for the least money. Tubing in 1000 or 1200 ft rolls is cheap and the cost of an extra loop on a manifold is almost nothing. More tubing with thoughtful layout is the way to go

 

[stingry]

You are not heating the air -- it's like standing by a fire outside.

Yes and no! Ultimately the air is heated but you feel warmer than you would normally at a given air temp due to heat radiating from the floor. I keep the air temp at 65 degrees at 5 ft above the floor but feel as comfortable as in my house at 73 degrees with forced air heat.

 

[extropic]

No one has mentioned what energy source you're using to heat the water?
Please elaborate.

 

[yeldogt]

Yes and no! Ultimately the air is heated but you feel warmer than you would normally at a given air temp due to heat radiating from the floor. I keep the air temp at 65 degrees at 5 ft above the floor but feel as comfortable as in my house at 73 degrees with forced air heat.

It's the way the body feels eat ,,,, there is convection and radiation.

BTU's are BTU's

Radiation will effect a tstat


Warm air rises ...

 

[69gp]

First off im not an expert in plumbing or heating. This is my take. First I see that you are from CT. There is a company in West Brookfield MA that make the Crete heat panels https://crete-heat.com/. They sell the 2" 2nds for $4.00 each cash. I bought all my insulation from them. The defect is the plastic sheet is not lined up square on the insulation. Lay the tubing in between the knobs step on it and your done. I did put down 8mil plastic under all the insulation.

I think the theory here is you want to have the tubing on the bottom as heat rises and the more concrete on top of the tubing the greater mass for heat storage. I did put mesh over the tubing after it was all laid in just in case it popped out of the knobs.

Also don't forget to install a conduit into the concrete for monitoring the concrete temperature.

 

[Evilcactuar]

Oh man, wish I knew that before! I bought 2 1/2 reclaimed foam, I would have gone for the creteheat for that kind of money!

The heat source has yet to be determined, but the concensus seems to be a propane system would be less costly

 

[like2wheel]

First off im not an expert in plumbing or heating. This is my take. First I see that you are from CT. There is a company in West Brookfield MA that make the Crete heat panels https://crete-heat.com/. They sell the 2" 2nds for $4.00 each cash. I bought all my insulation from them. The defect is the plastic sheet is not lined up square on the insulation. Lay the tubing in between the knobs step on it and your done. I did put down 8mil plastic under all the insulation.

I think the theory here is you want to have the tubing on the bottom as heat rises and the more concrete on top of the tubing the greater mass for heat storage.

Actually hot AIR rises, but I'm pretty sure conductive heat radiates in all directions equally. They say it's better to have the tubing closer to the middle of the slab but that's not always practical.

I'd be more concerned with how much of the tubing is NOT in contact with the concrete where it conducting instead to the insulation on the bottom & the sides at each nub.

I'm not an expert either, so this is just my personal take.



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