I hate to bring this to your attention,greenhouses are not really used for growing,well not this plant anyway,I live in ohio and start all my meds in my little 12x12x9,I have 2 exhaust fans at roof level one intake at floor level,and 2 fans moving air,all controlled from a central greenhouse controller,it checks temp,humidity,co2 levels,it is a very tough grow in a closed space,but hell aren't you from oregon,aren't you a legal state,why the greenhouse,temps in the 199's are going to bring you extermely long leggy plants,with no where near the size needed to pack on flowers,anyway you will need at least a good exhaust fan on a temp control box,that will at least part way there,you can also set up a misting system close to the roof that comes on in sink with your exaust,good luck,and enjoy,hope I was some help,it is alot of work