Thanks for your comment! Holes in the plastic are a double edged sword. They certainly will vent excess heat, but also allow any applied heat (which costs $) to escape. The easiest and cheapest option is to simply prop open the greenhouse during those warmer days. But, for a more automated solution, we opted to put our greenhouse on a plywood base and connected temperature controlled fans to a couple of holes in that base. These draw cooler air in, helping to maintain the temperature within the greenhouse. Hope that helps!

I want to build a rectangle shaped green house that you have described/built. However, I would like to use the heating pad instead of space heater. But I am wondering what’s the best way to ventilate such a set up. Is it enough to poke some small holes in the plastic? Would that work? Just curious about your thoughts.

That’s a great question, which I didn’t address in this article. One method would be to use conduit clamps, sized for the PVC you use. (e.g. 1/2″, 1″, 1.25″, etc) One side could be loosely secured, to allow almost like a hinge-like operation. Alternatively, you could secure the entire operation with bricks, rope or some other mechanism. (Like perhaps two weights, say bricks, at either end with a rope tied between.) In general, you’d want something easily removable so the greenhouse is accessible and generally avoid things that will permanently secure the system. We don’t have super high winds here, so it’s not often something I consider. But, as long as you’re not having to secure against tornadoes and hurricanes, a reasonable amount of protection should be adequate.