A device is disclosed providing an adjustable endcap for use with distribution conduits in a greenhouse. The device provides a solution to seal off the end of a distribution tube while providing further means to regulate the distribution of substances such as air or gas. The device comprises a structure for sealing the end of a greenhouse distribution tube wherein the sealing structure can be freely adjusted to allow variable amounts of air or gas to escape from the sealed end. The device allows for further regulation of pressure and temperature inside the conduit, extension of climate control over a greater distance and the ability to regulate conduits on an individual basis.
