Radiant Heat Insulation

Mark Hansen

I am a heating novice building a 30X50' garage and putting in radiant heat with a couple of propane ceiling heaters to get a quick jump on the heat when I first go in. I am thinking of putting a 3/8" insulator/barrier extruded polystyrene with 3 mil on each side down before I lay the the cement. I saw this stuff on ebay. It has a K-Value of .019 and an equivalent R-value of 11.7. Does this seem reasonable? Should I put on the inside on the outter walls b4 I backfill? Thanks for your help. Mark

Constantin

Thermal Mass...

Unless your slab is going to be very thin, the thermal mass is going to get in your way of heating it quickly. Your money might be better spent on eliminating the propane heaters and improving the insulation to a point where the propane heaters are not needed.

I find the claims of thin-film radiative barrier coatings hard to believe. They may work in an attic, but I doubt they'll do much more than create a thermal break below ground. I'm sticking with 2" of XPS below our basement slab, which should pretty much insulate the slab from the ground below. Ditto on the exterior of the foundation wall (at least below ground).

Above ground, historic requirements mandate the use of 4" brick, so only interior insulation will be at work there. If you have open cavity walls at the moment, consider foaming them with Icenyne or better. That, along with good doors should cut down your thermal losses significantly.

Considering the cost of all your options, your efforts might be best spent on doing a proper heat loss calc and then evaluating the cost and benefit of each option. If you're serious about radiative film barriers, look no further than Glacier-Bay for a fairly comprehensive trashing of radiative barrier claims versus real-life results. Naturally, one could make the argument that Glacier Bay is somewhat biased since they make $$$ VIP's. However, I have found their claims to make sense.

Justin Gavin

Don't forget the Perimeter

Stick with 2" foam or try Insultarp. We use Insultarp alot with 1" around the perimeter down to the frost line 4' in my neck of the woods.

Insultarp also acts as a vapor barrier.

Also instead of propane heaters get yourself a couple of Hot Water Fan Coils (Sterling or Modine come to mind) if you have a suitable heat source. You won't need to vent which means less holes in the roof. Also you may consider using a heat exchanger with glycol to stop the tubes from bursting. I had a boiler failure this fall on a cold day
(-15) and we had a section of Pex Burst. Nasty business. Had to chip the concrete and throw in a coupler.

Good Luck,
Justin

Good Luck,
Justin