One of the handiest things in my g/h is an automatic vent which opens when it is hot. The mechanism is available from Lee Valley. I use my g/h which is very small, for overwintering some plants and for spring starts. I have a fan going 24/7 -- if you don't do this you will get mildew and if the temp is going much below freezing, I turn on an electric heater. I think that if plants are aclimatised to such cold conditions, they can stand a few degrees of frost. We haven't had a really prolonged cold spell since I have had the g/h. It is so small, I think if a real arctic blast was predicted, I would move the plants I really cared about. It is fun though to be out there in early spring when it is still cold and watch the seedlings coming along so well.

There is a greenhouse forum here at Garden Web. I've found it very helpful. DH just bought me a greenhouse.

Here is a link that might be useful: Greenhouse forum

Charley's Greenhouse(www.charleysgreenhouse.com), based in Bellingham, by the way, is the absolute best at explaining the mysteries of a greenhouse to a beginner. They also sell accessories.

Thanks for your suggestions. I'll check them all out. I'm excited!

As you should be!