DIY, that's great! I love building stuff it looks fantastic (of course)! [img]http://www.**********.com/iB_html/non-cgi/emoticons/smile.gif[/img]
Carnivorous Newbie the sun beating through the glass or poly plastic sheeting will warm a greenhouse during the day even in winter. It's mainly nighttime when you need a heater to keep the space warm. In a smaller room like 8 x 12 or so you would probably be able to use an electric space heater or two from Walmart or something. Big freestanding structures (like I wanna build - at least 30 x 100 sq ft) will need a huge heating system of 200,000-300,000 BTUs.
Nep G there are some plans for a swamp cooler in Orthos "All About Greenhouses". They aren't very detailed but it looks pretty easy to setup based on the diagram. Did you find the plans for yours online? I'd like to look them over if you have a URL to post.