This is how I am doing it this year. I only have enough room on my McSuburb parcel to have small-scale structures, so this year for experimentation one of the things I have is a 4 x 6 coldframe (walls insulated at ~R-5) with a below-ground insulated structure, a water-tubing subsoil heating system and ~30 liters of water for thermal mass. The glazing is 8mm twinwall polycarb at a 30º angle and at night I cover the glazing with an old sleeping bag. Further, I take some of the heated water and put it in the soil, which is insulated @ R-6 - down to 10" in a raised bed next to the house. Despite numerous days with highs in the single digits F (-15ºC ) and several lows well below 0ºF (-25ºC), last time I checked my soil was 64ºF in the sun and 58ºF in the shade (~18ºC and ~14ºC). Air temps during the day always need to be vented on sunny days and at night I have never dropped below 35ºF (2ºC), even on the night we hit -14F (-26C). So my dark-colored water and soil are my thermal masses. So, to reinforce anecdotally what is above, IMHO the original link had inadequate mass to keep from freezing for that volume. The glazing insulation is important. Any text on solar houses or solar greenhouses spend considerable time on solar access and solar mass, as well as insulating the glazing at night and opening the glazing to the sky as soon as the sun is up. For example, right now the coldframe has heated up ~4ºF in 3/4 of an hour's exposure despite cloud cover allowing only ~40% of the expected cloud-free solar radiation through. The sun is free energy. We must do more than just collect it to make it work for us. We must store it, distribute it, and insulate our glazing. Dan

I got my louvered fan at ventilationdirect.com. I got a 10", but they sell larger ones. I think my fan was under $90. I found a great deal for my automatic louver on ebay. I got my thermostat from kkontrols.com, but Farmtek is cheaper. I have both my fan and louver hooked up the the same thermostat. The louver draws very little power and can easily be hooked up to open with the fan. Stuart

Fuzzy, it may be time for you to do a "desired lifestyle & available time to enjoy it" check. You built a GH for pleasure. Please don't tell us it was to feed your family, because the simple truth is that building and operating a small home GH is far more expensive than simply buying fresh veggies and if you are into all natural, there are plenty of shops around these days to accomodate you. In fact, you could shop exclusively at Whole Foods and still not spend what it costs to build and operate a small home GH. Ergo: you built it to ENJOY it and unless you are independently wealthy, the TIME available to you to ENJOY it is when you are NOT working to earn the $ it will cost to operate it. So don't get so wrapped up in gadgets that you end up spending as much if not more TIME messing with the mechanicals than you do puttering with plants. Perhaps it's my age, but the older one gets, the more one appreciates TIME- The Great Thief.

Probably too late to post this info now but.... I have been playing around with inflation blowers and my extensive research has shown that a shop-vac, although spectacular to watch in action is way too big!!! On the other end of the scale a small 12v PC fan inflates the poly but cannot provide enough pressure to inflate it tight enough. However, because I was bored I hooked up an old one of these things I found. http://www.performance-pcs.com/catalog/index.php?main_page=product_info&cPath=145&products_id=1150 It is slow to inflate but once the poly is inflated it maintains a decent pressure. It draws 0.15 amps at 12v. I have it experementally hooked up to a 17Ah battery so in theory (yeah numbers again!!) If I let the battery go down to 50% capacity it should run for 57 hours. Hook it up to a truck battery and it should run a month. If anyone is interested I have pictures but at the moment I can't FTP. Here is a link that might be useful: The blower I have.