"yourname" wrote in message
...


I laid down 2" Certifoam and used the plastic chairs made for this
purpose
that screw into the styro to clip on the tubing. I also insulated the
edge
of the slab as they say that is where the biggest heat loss is. Best
investment I ever made!
Steve




Yes I should mention that I have 2 inch foam under my garage floor, a
bit of a leap of faith but it hasn't cracked yet....spose you wouldn't
think twice at pouring concrete over compacted sand, and it will squish
underfoot, but foam seems wrong. If you are concerned about point
loading [a punch press or something] you could insulate well[deep]
around the perimeter. I loses some efficiency over insulating under but
you have a large increase in thermal mass[all the dirt]


Typical foam insulation found in building supply houses runs from 15 to 25
PSI. It is available as high as 100 PSI compression, so there's no good
reason to not use it. I installed 40 PSI stuff under my 6¼" thick floor,
which has ½" rebar @ 18" centers both ways, to which I tied my heating
hoses. The rebar sits on thin dobies, so the heating hoses (mine are
rubber---a Heatway/Watts product) are down about 4". I run a forklift
that weighs 5 tons, along with a 3 ton load, and have NO cracking aside from
the original scores that were intentionally placed for controlled cracking.
The rebar, which I highly recommend, prevents any settling and shifting of
the cracks.

There is no better way to heat a shop---especially if you don't like cold
feet.

Harold