Hmmm, out of curiousity, what kind of turtle is it that it needs additional heat over the winter? I take it that it is not a native species?

A cautionary note: small green houses tend to build up heat rapidly. In no time at all, unless you have it set up to vent off the heat once a certain temp is reached, a small greenhouse can quickly reach temps that will be lethal to her turtles.

The old way of making hot beds was to dig a pit maybe three feet deep, fill with two feet of manure and top with a foot of soil. then cover that with a frame.

I knew someone who kept finding turtle skeletons in his compost pile - they would crawl in there to hibernate and get cooked.

I figured if it got too hot they would just stay near the side. I guess it makes sense, they can do dumb things. Apearently they think if they can get their head through an opening that their body will fit also. Hows that for an out of whack body self image:) I was thinking of letting only a side or 2 of his house be heated so he doesn't get cooked.
So birdgardner, will that hotbed also stinkup the greenhouse and does it need to use the whole floor?
Thanks, Damon

turtles go dormant in the winter just like plants do.

Actually he is an african tortise and getting near 60 lbs. He will be getting over 200 lbs over the next several years. Eventually I may not need to ever mow my bermuda grass with him around. He doesn't hibernate and when we tried an unheated house he caught a cold and had a snotty nose and was wheezing. I found a mother earth news solar regulating greenhouse design that looks good. It seems that most of the greenhouses use a fortune in energy heating during the winter and then nearly as much in the summer cooling. Its nuts. Any one here ever make a passive solar greenhouse? I've been collecting old windows for a year now.
Thanks, Damon
PS I may be heating parakeets now also.