Leafy Creations Replacement Piston for Greenhouse Window Openers Automatic. Temperature Controlled Greenhouse Spares and Accessories for Cold Frame and Greenhouse Vent Opener.2 Pack. Simple self installation, please watch the video in the images and read the product description below for a simple to follow guide on your replacement greenhouse window opener. If your greenhouse automatic window opener has stopped working, simply replacing the cylinder will restore it to normal operation, no need to replace the whole vent opener. Compare with your existing opener, if the piston looks and measures the same, then its the same.