You betcha, C6. Vegetable production is a way of life for me, second only to guns. Cold frames (under glass) require constant, and I mean constant, monitoring to avoid overheating. I know from experience, having fried my share of expensive seedlings. No room for error; it can happen literally in seconds when one is lulled into the false sense of security of a cloudy day and then have the sun come out, even if briefly. I quit using glass years ago as a result, instead, I use uncovered frames which still offer protection for germination and the emerging seedlings. To provide heat for the frames I once built a pile of dampened compost materials mixed with purchased blood meal for an oxidizer. When I turned the pile a few days later to speed decomposition, steam billowed out, the pile was spread to make a bed perhaps ten inches deep, and seeded flats were then placed on the heating compost rather than planting directly into the bed thus formed. Lots of monkey business but one can indeed get a bit of a head start without the danger of a glass-covered frame. I can't stress enough how tricky covered frames can be; one may cover the frames for overnight protection but must uncover promptly at sunrise! Old storm widows are often tried, but screens are actually more useful, providing some protection without the danger of overheating. Of course, I'm talking about seed starting here, not "growing out." Those I know who've tried growing to a larger size under glass report even more challenges. The tunnels shown in the Williamsburg link are actually all the rage as of late, termed "low tunnels" and "row covers." You may find Johnny's Selected Seeds catalog helpful regarding those items.
