I asked for advice and got it, didn't I? The trouble is, I didn't use it! I went to the Johnny's site and saw the premium model, but like Goldilocks, it was toooooo big. (I measured the footprint of where I want it to go, and even the smaller ones seemed really big.) I went to the other places where posters provided links and looked.... I didn't want to have to drag tables or shelving out and an 8' dimension (eiher way) is too big because there are roses right there with some SERIOUS canes. I only plant to keep it up in March and April, possibly into May, but that would be to keep plants dry rather than warm. Then I looked at some simple little upright ones. I think you could put one flat on each of the three or 4 shelves, but they were tooooo small. A heater would probably burn the plants closest to it. Then I went to Ebay and looked at all theirs and looked and looked and finally decided on a little 4 x 6 with shelves. It is NOT a good one. The plastic is reinforced, but there is no venting. Not real sure that was too bright, but we'll see. There is no anchoring at the bottom so it could also blow over (often times these come with little ground stakes) On the other hand, the price was right and I really just wanted a large germinator. It is a walk in model, so in a pinch I could put a heater in it without melting the plastic. I love wintersowing except for two things: the milk jugs look like hell and now that I am midway into it, people are talking about taking the tops of the jugs when the sun is shining & it's warm out, and then putting them back on when it's cold! I thought you could leave them out there on their own! No way I am babysitting 300 jugs next year! If only it had some vents, I would be really, really happy, but as it is, I just want to see what kinds of temperatures I can expect. As cheap as it was, maybe the reinformced plastic will rip right off the bat and those will be my vents :) Thnaks for all the insight, though. I enjoyed all your posts and collective thinking. Lime

soycandle, I might not even ought to post because I am not in your climate zone (I am in zone 8B) and have no experience with the type of winter you have, but...that said... I have had a portable greenhouse for 5 years. Its the same basic type as yours, from a different company. Mine is called a "Groenhaus" and it came from a company in I believe Norway (may have been Sweden, but its one of the Scandanavian countries where they have an actual winter with snow, ice and wind.) Mine has a steel frame in a hex design, air vents, and zipper door. Its made of 12 mil woven poly fabric, and conducts about 83% of available sunlight. The cover is thick and insulates very well. I myself live in Northern Florida where there is no snow, no ice, but it does occasionally get down to 20F once or twice a winter. I have had GREAT SUCCESS with my portable greenhouse. I have used it to overwinter tropical plants that were containerized (plants like heliconias, Ti leaves, gingers, aroids like anthuriums, orchids, bromeliads....) I have also used it one winter to cover a 6 x 6 raised pond that had tropical water lilies in it, I also stacked in a bunch of containerized plants in with the pond and they loved the humidity...currently, I leave the base of the frame on the ground year round, surrounding an outdoor inground planting of tropical plants that would freeze even in our relatively mild winters (Alpinia purpurata, Heliconia, bromelaids, Ti leaves, birdsnest fern, etc) and erect the cover over the bed in winter, then take it off in spring. These little portables work GREAT. All you need is to put a portable ceramic space heater (the kind with a thermostat) inside the grennhouse. For your size house, 6 x 8, one 5120 BTU heater will make it toasty for all your stuff. I have the type that you can set the temp, the range is 55,60,65,70,75 and 80. The heater goes on and off automatically to keep the GH at the temp you choose. The heater has a built in fan and blows warm air out, and it oscilates to help distribute the heated air more evenly. Its also helpful to have a small oscillating fan that you can hang from the frame in the roof to circulate air and heat. This cuts down on consolidation and also on algal growth and pests. I see you are in zone 5...it will of course take you more electricity usage to heat your greenhouse than it does me, but it also depends on what you are growing....I keep mine at a minimum of 60F, but the plants you are growing may only need above 32, or the 40-50 range. I would think you could go on and set the thing up and start using it now. The only advice I would offer additionally is, if your winter storms include WINDY CONDITIONS, be certain you use any tie down apparatus (stakes, guy wires etc) that they offered you. Without them you run a risk of the whole thing blowing over in a high wind. I think of mine as a big, almost clear TENT that my plants are camping out in.

Forgot the little decimal. I thought that was a lot. I only used 3 - 1500 watt heaters for my greenhouse. But of course I had solar pool covers, and extra layers of plastic and 7 - 55 gallon rain barrels with water. I had ice on the inside of the windows a few nights. Even in my zone 7, 34 for an outside low temperature is stretching it. And we often have a lower wind chill factor. So for a zone 5 area it can get down to -20 and the greenhouse needs to be above 32 or 34 because that is not enough of a buffer before freezing. So using those figures: 177 Area of greenhouse -20 Outside temperature 38 Inside temperature 1.20 Heat loss factor ------ 12,219 BTU's One 1500 Watt heater produces approx. 5200 BTU's(varies). So that means approx 2 1500 watts and one 750 watt. My three (3) 1500 watt heaters and a ceiling fan cost me $100+/- per month. I can justify that for my 32x37 greenhouse filled with collectible tropicals(AeAe banana, Amorphopallus Titanium(The worlds largest florescent), Rare gingers, citrus, palms, etc). But that would be some expensive tomatoes. And the 3 heaters would take up the space of three pots, plus there would need to be space away from the walls and plants so they don't catch fire. But IMO the heaters would ignite the cover or melt it. Anyone want to try it and report back in the spring??? LOL

I use a 29k vent free propane heater as my sole source of heat in my greenhouse.It's one of those "Wall Mounted" heaters they sell at home depot.I guess you could buy a 9k btu ventfree heater,and it should work perfect.I went with propane because of the ice storms we get here every few years.