I had it set to 76F last summer and had no problem maintaining a constant temperature. My electric bill went down by almost $100/month in the summer of 2006.
I highly recommend the radiant barrier as a solution to Florida's hot attics and high electric bills.
Callie, the crete-heat install was so easy. My wife and I did this on our own with no experience whatsoever. The 2x4 panels our very easy to handle, wind or no wind. I can only imagine what a pain it would be to have to measure out where to put the tubing, (which by the way was so easy to install due to the molded knobs of the crete-heat) much less have to use wire staples of some sort to hold the tubing in place. There were only 2 locations on somewhat of a tight turn that we had to watch when we poured the concrete to make sure the tubing stayed down. Not a cheap product pricewise, however, not in quality either. I had some pretty big boys helping with the pour and to the best of my knowledge, we did not poke or tear through the tough outer coating at all. Awesome, awesome, product!!! Would recommend to anyone installing in floor radiant heat.
If the next product I get from you is comparable at all, I am looking forward to seeing it.