Seems one would want to have a good way of monitoring the heat that will build up in the pipe, so as not to boil water in one location and also not to melt the solder at all the joints in the heat run. That would not be fun.
I have seen this welding trick work with underground pipes. I would think the plumber of Hazmat's might know how to do that.
I don't have zone valves in my three heat runs, but have pumps instead. I leave the pumps run a lot to be sure the water doesn't sit too long when it is real cold outside. If I ever have to leave the house, I plug a light into the pump that services the bedroom area and turn the heat down on that thermostat to about 55 degrees, and leave the doors open to the living room. Normal heating of the living room area will keep the bedroom area warmer than 55 degrees. If there is a failure, and that bedroom thermostat calls for heat and that pump kicks on, the light also comes on which is in the living room window. The neighbor knows that if that light is on, there is no heat in the house and calls the heating co. for me. Only needed it once, but sure glad it was in effect when that time came.
