So I ran into a problem where my 4 inch exhaust fan (runs 24/7) ended up being too powerful for my 2x4 tent causing a lot of negative pressure even on its lowest setting. This wasn't too much of a concern until I realized that it was also taking away too much heat (tent is in basement) and the grow itself was sitting at a high of 67 degrees with my 1000w led ON, with only being able to get the temp up by shutting the fan off. I looked online and sure enough they had heat sensing timers but they were extremely expensive and the cheaper ones (~$80) had bad reviews with possible risk of harming the fan itself. On top of this, many of the timers leave the fan completely off which is not ideal as there won't be any air exchange occurring. After a little thinking I thought of this "brilliant" idea! ________________________________________________ THE LOGIC At its core the duct fan is a vacuum, much like a house-hold cleaning vacuum it creates pressure/suction. Most cleaning vacuums come equip with a suction vent on the nossle that allows one to change the amount of suction the vacuum has. PRESENTING DIY VARIBLE SUCTION Exact same idea as the variable suction on a vacuum. This modification will allow you decrease the pressure of your duct fan giving you complete control of how much air is exhausted! *I know this might not be the best solution, but it worked fantastic for me (cheap) so I figured I would share it with you guys in-case someone has a similar problem. (tent now sits comfortable around 71 degrees, 4 degree difference) YOU WILL NEED - two steel duct clamps - spare drier duct piece - foam tape (optional) - scissors - xacto-knife _______________________________________________ EXAMPLE DIAGRAM STEP 1: Take your scissors and knife and cut the desired hole in your ducting. Make sure you start small and make larger if needed. *DO NOT cut hole close to fan, the closer to the tent the better. STEP 2: Take the spare piece of ducting and cut it in half so it is a half circle. The size you cut is up to you just make sure it is large enough to cover the hole you made. Take your *optional foam tape and cut it into strips long enough to line the inside of the half piece of ducting. This step is not completely necessary but it will allow for a better seal if / when you want to close the hole. STEP 3: Place the spare half of the ducting over the hole to the amount desired and install both clamps. STEP 4: Slide the "vent" around the ducting to increase and decrease the pressure/temperature inside the tent and tighten! STEP 5*: If concerned of large debris entering duct hole and damaging fan you can go a step further and add a screen, just be sure it is held securely in place as you don't want it to get lodged inside! ___________________________________________ Additional pictures:
Credit for nice pics Russian method here like on space station is to undo one of those pipe clamps loosing it off until you have achieved a balance mark it with tag to remind self later or insert pot scrubber from kitchen to vent pipe ..lol good luck