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.)

Did we come to an end on this thread? ""Let's brain storm: thermal mass materials"" I think we agree for all practical purposes then water is the best for thermal storage. Several interesting issues emerged and I think they are important. "Seems to me is we may be switching our night time heating bill to a day time heating bill..." Yes, that may be a bonus in an unconventially heated greenhouse. During the day it may involve stoking up a wood, corn, straw bale, oil fired furnace to build enough heat to get through the night. In gbrendemuehls scenario you just have to do the "burn" once every three days. ""3 day storage reserve and and 50 degree termperature range, the needed volume of water is about 4600 cubic ft. or 34,500 gallons"" In the test greenhouse that is just under 2 feet deep. Why is that not practical? I admit that retro fitting a 34,500 gallon under floor holding tank in this case is not possible bit in the next one...... ""Large greenhouses are built on a grade of about 1 to 2ft per 100. Insuring the any water on the floor/ground will run out of the house."" You heard the latest the EPA are throwing at us? Greenhouse waste water is going to be classed as toxic waste. (as it should be.....) Don't ask me for a link to verify this because I have not looked. However I do know I am the only one in this area with a greenhouse because the other guy who ran a commercial setup quit when he got slapped with a $17,000 water treatment bill. Storing and re-using the run off may be a side benefit. The most important issue for us may be the fact that this thermal mass, free heat concept does not scale up to large commercial operations. We all know it works down to the "Wall-O-Water" level and up as far as 150 gallons of water under a 4x8 bench but to take it past that point you are looking at some really big heat exchangers and pumps. For Mylu, For you, the only benefit a water based heating system with the water under the benches would be is that with a prolonged power failure you would not lose your crop.

A couple or three possible FAQ questions: What are the recommended procedures for preparing the foundation for a greenhouse or greenhouse kit? (depth of excavation, burying foam insulating panels to restrict heat conduction into the ground, installing hardware cloth as a barrier to rodents, sand, crushed rock, perforated plastic pipes for drainage, etc.) How do I keep the copper in the pressure treated timbers from attacking, corroding, and even dissolving the attached framework of aluminum greenhouses? How do I protect a lean-to or attached greenhouse from falling icicles and snow slides from the eaves of the house? MM