Yep I have power, run fans and a soil heating cable on it now. I try to overwinter some sub-trops every year, and they don't like it much when temps go below 45. I don't want to pay to heat it that much. This seemed like a fun project (SHCS), I was wondering if anyone in a mild climate had experience with using one, and how well it worked.

6x8 is pretty small. You really need to be bigger. University of Vermont has some good info on "high tunnel" greenhouses. An HT is low tech greenhouse. University of Missouri has a good design for a barrel moderated greenhouse. Barrels don't stratify as much as you'd think. During the part of the year you want heat, the light is striking them on the side. With the warmer water on the side, it powers the circulation. If they are open top barrels, put a divider in them. Coreplast works well for this. It should fit the diameter of the barrel, and about 2" from the bottom and top. (Put 'ears' on the bottom to keep it from sliding down.) This divides the barrel into a front and back half. Now water has to rise on the front and fall on the back. May have to play with that 2" dimension. (You want 2" of water over the top edge, and under the bottom edge.)

I'm in the same boat as you Dave. I certainly don't need the heat and I'd rather have the space. I was wondering if they might help keep things cooler during the heat of the day, but it doesn't seem like it would be all that effective. So I've been emptying them over the last couple weeks, whenever I need some extra water for the lawn.

Thanks for your response Robert. I'm not looking for quantity in my GH, just quality and economy. Heating a GH with fossil fuels or electricity costs too much in my opinion. I only have 2 mouths to feed! I want to grow some lettuce and stuff for fresh salads, without worrying about salmonella. Use it for starting tomatoes, peppers, ETC. Extending some tender veggies later in the fall. When I was younger, and had my really great greenhouse, I had tomatoes almost year round. I had a tomato that lived for 3 years! It might have lived longer, but I had to move. I drove by about 6 months after I sold the house and the new owner had tore it down!!!!!! I felt really sad!