Hi All, Thanks for your response. Cactusfreak - where did you purchase your pool cover? I have been planning on getting one of those eventually. When I bought the greenhouse I thought it was much more insulated and a lot of people (including the distributor), told me it would be more than warm enough with two oil radiators. It sounded like I would need more heat than that, but I thought it would work out. I think what I will do for this winter is insulate the greenhouse like crazy, get a good heating system and hope for the best. I'll have to look up Pittsburgh's weather records as well for the winter. If it doesn't work I'll just use it as a cold frame. I will be growing a bunch of orchids in the greenhouse and a handful of 'annuals' including Fushia, hibiscus, mandavilla and more. Some of the orchids are probably the most sensitive to the cold.

Bruce, thanks for the info. . . it looks like I can let the lizards stay in the greenhouse without threatening any ladybugs I put in there. I have seen the cats catch mice at times, and once in a while a gopher, and I assume they have caught much more. I have brought down a lot of flat rocks stacked here and there, for landscaping and retaining walls and so on. There are so many openings that the lizards dart in and out of that I don't think the cats can catch them, but likely I have just not seen it happen. If they are catching the lizards they are only partially successful as there are so many of them. I did not see so many of them before I began to bring the rocks in from the surrounding hills so it may be that they were being caught before but now have an environment that protects them somewhat. We have more gophers than I can count and that is a constant battle with maintaining a lawn, and have many squirrels, and snakes of many kinds. I am told that when the gopher and squirrel population is high that it will cause more snakes to stay around (we have rattlesnakes) but then they will go away when the population is reduced. I don't know if that is true, but have noticed that the number of rattlesnakes is down from when we moved here 22 years ago. I have also been told that they stay away if there is a lot of outside activity. . and we are outside a lot. And we have a lot of wild pigs which I am told will kill the rattlesnakes. . .but I don't know if any of this is true. The coyotes took out the chickens and try to get the cats. It's an interesting life.

The rose isn't the same as the tomato. For one thing, one isn't trying to "ripen" a rose. In the rose greenhouse, such high temperatures could not be tolerated. 85 was as high as the greenhouses were allowed to go. Overnight, winter and summer, temperatures may drop as low as 60 before the furnaces would come on. (I think I'm all dun trying to use the degree symbol. GW doesn't know what it is usually. I could say something about GW being as archaic as the Imperial system of measurement but I suppose I'd be off by centuries. ;o) Before the marketing industry turned to Columbia for the majority of our roses, Colorado was thought to be an important center for rose production. Your abundant winter sunshine, makes the state a very good choice for winter growing. Ventilation is important. When outdoor temperatures are low but the sun is bright, roof venting is the way to go. Often, it takes very little for the warm air to escape. Steve

I know it has been a long time, but I think the calculation used is to determine if you do not need any make up air or not. If you are under that then you use the separate calculation to determine the amount of make up air for combustion. For a single supply for combustion air it is 1 sqr inch per 3000 BTUs of your appliances. For 2 supplies, 1 within a foot of the ceiling and the other a foot of the floor it is 1 sqr inch per 4000 BTUs. For example a single supply 225,000/3000 = 75 sqr inches. A 10" pipe has 79 sqr inches.