I am curious to hear what has been going on with these or other passive heat systems since this discussion started.
The past couple winters, I've used an electric hot oil heater, which heats well, but the heat is lost so quickly, it has trouble keeping the temp more than 10° higher than outside. That was enough the past couple winters, with the season low in the mid-20's, but if a really cold night hits, probably night. This season, I'm going to build a wall of water bottles painted black around the 3 sides in the sun and will report back here about the progress and the results.
I chose this material because we have these bottles in abundance (once I stopped taking them to the recycle bin, which I will do with these once they have performed a re-use first.) I plan to lay them flat on the ground, and stack them up between stacks of bricks at the ends to hold them in place. I don't expect this to heat the GH because it will be on the outside, but to help reduce the speed at which the heat is lost, more like insulation.
