When I woke this morning it was 15F with a wind chill of -5F. My lettuce made it through the night in my greenhouse.The temp in the greenhouse was 31F. Soon as the sun comes out the temp in the greenhouse goes up fast. Right know its 21F outside and the temperature in the greenhouse is 62F (wind isn't helping much today) Here is a pic I took this morning.

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This post was edited by hartford on Sun, Nov 24, 13 at 16:04

If your GH is located in PA, I'd say that's pretty amazing! Looks to be about 6' x 8'? Have you done anything to winterize it?

Its a Harbor Freight 6 X 8 Greenhouse. I didn't do anything to winterize it. I put 2 - Black 30 gallon trash cans filled with water in it. I also have an electric oil heater I keep on low at night when the temps drop below 32F. The temp in the greenhouse during the day is usually around 85F degrees when the sun is out it warms up the water in the cans pretty good.

I have the same GH & have done some foam/sheet (on floor) insulating & caulking plus run a 1500 watt elec heater and an overhead fan......... Our winters are mild compared to yours & my results aren't nearly as good..... Seems my heater has to run full blast when temps drop into the teens, just to stay above freezing at night...... Guess I need to rethink my strategy.....

If I were to install this GH, I would position it such that the entrance end ( or alternatively the opposite end) is facing NORTHWEST(one of the 8ft side facing NE)
Then I would make the side to the left (NE) solid insulated structure, that would include that side of the roof as well. I would do the same on the NW facing end as well, but have two small windows, one on each side for visual effect.

To me this is a winter greenhouse. If it is sunny, you will get plenty of solar heat from the remaining 50% glass structure. ((That is where most of the solar heat is coming))Maybe even more than what is needed. But even during that sunny period you will be having considerable heat loss through the NORTHEAST wall and the roof, if it is glass. This design, that I recommend, will further curtail heat loss/cooling during the long hours of night and you can better manage to provide a backup emergency heating system.

It's been below 15 several times already this fall (almost to 10 once) and still going strong in the open garden, covered over with double row covers are winter lettuces, savoy cabbage, collards and kale. Covered with hay and remay are beets, carrots and turnips. Spinach is going stron with no cover at all.

We've been down to 23 here, and also had snow. Assuredly the coldest earliest weather since I have been here since 1981.

Very pleased with my collards. I had left about ten unpicked outside the hoop houses, they suffered through multiple sub-15 nights, with 96 consecutive hours of freezing weather. But yesterday afternoon it went above freezing for about 5 hrs. They popped back up and were promptly picked, about 40 lbs before cleaning. Lots of greens, obviously I will not go under the hoop houses until after Christmas.