How far under the concrete can I go?

eluv8

The thicker the concrete the more mass you have to heat, the closer to the surface the better, Ideally 2 to 3 inches below finished floor.IMO. I have installed tubing as deep as 7-8 inches placing wire mesh on top of the abc and tying the tube down to it with a concrete overpour. The tube was at the bottom of the slab with no insulation, except the perimeter 2 ft in. In reality with no insulation the heat is going to migrate down anyways. If you place the tube in the abc layer there will be, in a sense, a thermal break in conductive heat transfer,I would stay in the bottom of the concrete pad minimum. This was for a residential home. It responds slow so I had to use outdoor reset and 10 degree delta T. It works fine MOST of the time. If weather changes fast it cant keep up very well with the changes. Dow Chemical makes a hi density blue board for commercial applications and have a psi rating for underslab use. Comes in 2x8 and 4x8 sheets I highly recommend its use at least around the perimeter of the building structure stemwall and 4-6 feet in underslab to control heat loss to the outside of the building. GoodLuck sometimes the end user or other subs can be difficult to work with when it comes to putting tube and insulation in or under concrete, yet can offer no verifiable problems with doing so when done correctly, except when the insulation is placed between the abc and the concrete, it creates a vapor barrier and the moisture doesnt obsorb into the ground. Creates the potential for hairline fractures in the top of the concrete. A layer of sand on top works great or putting the insulation below the compacted abc base also works well but increases your thermal mass. ON EDIT; That is an incredible article, goes right with what I have been seeing in the field. Having a copy of that article will help immensly. THANK YOU SIGGY

Rich L.

Way under slab heat

I have a customer looking at building a new sheet metal shop that's interested in radiant floors. They have lots of heavy equipment that he moves around from time to time as well as anchors to the floor. He plans on pouring an 8 inch slab. He has heard of a local job that was done by another contractor where the tubes were placed in the rock below the slab, covered by 1-1/2 inches in fine rock and then the thick slab poured over that. Has anyone here done this? If so, any advice or photos?

Thanks in advance for any help, Rich L

ALH_4

Shallow

That doesn't sound like a very good idea. You might talk to the structural engineer and see how shallow he will let you put the tubes. You could use a wider tube spacing (possibly 24" spacing and tighter at the perimeter) and a simple tube layout for a shop like that, and document the location of the tubes very accurately. There is high compressive strength foam available for below-slab insulation, although standard XPS foam is probably more than strong enough.

A little effort now will save a lot of fuel later.

hot_rod

Bad idea

got to www.pmmag.com and look up the article "Depth Perception"

Siggy modeled the performance difference with tube placed at different depths in concrete.

Even in the bottom of an 8" pour would really require much higher temperatures, not to mention huge lag and wind down times.

hot rod

ALH_4

Siggy

There's also a Siggy article out there that models the performance of tubing in a slab at wider spacing. I know it was in the Jan/Feb 2005 issue of HPAC. Wider spacing will make it easier to miss the tube later if they drill for concrete anchors.