We've found these Bayliss Automatic Greenhouse Vent Openers to be the best on the market and are suitable vents for both wooden or aluminum windows and frames. With the two of the most important aspects of successful greenhouse growing being adequate ventilation and preventing excessive temperatures we are sure you will find these Autovents invaluable. Please note that although the XL Autovent will fit the vast majority of greenhouses, some models of Halls and Robinsons may require additional fixings. We also recommend the Bayliss MK7 Autovent for use on any Alton structure.