I posted earlier about a subslab insulation barrier using closed cell spray foam.  Here's a few pics if you want to see.  I am  happy with the way it turned out, and it was easy to staple the radiant tubes to. 

I used 3/4" tube, spaced 16" apart for one loop, and 14" apart for the other loop.  Both loops are a full 300'.

I'm interested in what you guys think.  The foam layer was more even than the gravel bed I gave them to spray to, I think they really did a nice job.  960 square ft, $1800, 1 hour, 3 guys,  but you ought to see the machine that runs it.

Ben

Interesting. How thick and what R value?

I never heard of 16" spacing or 3/4" tube for basement radiant before. Have only seen 1/2" and no more than 12" spacing to avoid striping. But I'm not a radiant expert so I'm not saying it's wrong. Just different than my limited exposure.

Greg,

The foam is a 2 inch minimum thickness, and I believe that translates to R10, but I'm not real sure about that number. 

We poured the basement floor today and  the guys said the crete didn't dry as fast as they're used to.  I wonder if it's because all the water had to come to the surface since it couldn't get through the sprayfoam.  Just a guess, but I didn't know what to expect since my flatwork experience is very limited.  We got it done though, I'll see how it looks in daylight.  Next time I think I'll just hire that done.

I'm interested in how the 16" spacing works.   My tube supplier says that's what he always puts down, but he is Amish and they're not known for indulging in comfort. 

Ben

12" o.c. max and smaller pipe is generally a better idea. You'll have some heat striping. That's not the end of the world, but it's not ideal either. You'll heat the space fine, you'll just be able to tell where the pipes are (and you spent more on pipe than you had to).

The product I use would cost About $1.40 per sq ft, check out Crete-Heat at  Sip Energy Systems.com

that is urethane, should be around R7 per inch. good stuff, i used to work for a urethane roofer, sounds like a decent price for urethane, we use to charge $5 a square foot for roofing 3" thick, but it had a uv resistant coating applied as well.