It would be a totally wasted investment to try to heat up the outdoors. Whether there is a breeze or not, the air is a huge heat sink which will suck away the energy and dispel it broadly to the neighborhood. Radiant heat is great inside — I have it — but it takes a long time to heat up the slab, and the slab does not even feel that warm when it is working. Radiant heat works by heating the volume of air contained in a confined space. If you had a really drafty house, it would cost a lot for the radiant heat to maintain a comfortable inside temperature. Outside, you would be wasting an enormous amount of energy and I doubt that you would feel much warmer than ambient temperature. if you want to feel comfortable outside, invest in one or two standard patio heaters.