Greenhouse vents from Harbor Freight
So last weekend a couple of nice medium high hoop houses went up. The only item of any significance left to do to finish them off was to build and install vents so that the spaces wouldn’t overheat.
Often it is hard to remember that even when the outside is cool the solar gain in a cold frame or greenhouse can be significant. Now before you’ve got plants growing I think it makes sense to limit air exchange so that you build up the thermal reserve in the soil – especially if that soil was frozen just a few weeks ago. But once the soil is thawed and plants go in it becomes imperative to ensure that they aren’t baked.
There are thermostatically controlled vents of course – but those rely on and use electricity. When I had my solar greenhouse I came to really like the vents that rely on the expansion within in a cylinder pushing on a lever to open vents. These have the advantage of being completely non electric and in my experience completely dependable. They aren’t nearly as controllable as electro-mechanical systems would be but they are pretty fool proof, low cost and get the job done.
Now, they are limited in what they can lift – think plastics not glass. If the bulk of your cold frame or greenhouse is glass just make your vents out of plastic material and you’ll be fine.
For my setup I made a frame to fit a couple of pieces of plexiglass that I was given when I purchases a pantograph from a sign shop in Montreal that had served Zellers stores but when that retailer shut down the sign company closed the associated shop. The owner offered me all the plastic offcuts – some of significant size – and professional paints and hardeners that I wanted. With the pantograph on my trailer I piled the bed of my truck high with the free material. As luck would have it I drove back through a massive police presence – escorts for a Hell’s Angels and Associates motorcycle ride that traveled along with me.
Anyway the frames were built from the remaining used pieces of 2×4 and some plywood offcuts. The plexiglass pieces were hinged at the top, with the screws extending through the sheet into hardwood sections salvaged from hockey sticks. The opener itself is fixed to the lower portion of the window frame and the action arm was bolted with the included bolts through holes drilled in the lower part of the plexiglass window.
By the afternoon the greenhouse was hot enough that the widow had opened, so now I have no more excuses to delay planting… maybe I’ll take that on tomorrow if it’s nice.