[hippylee]

I have a 8 x 6 ft foot grow room in the back porch of my house vented with a 6 inch vortex exhaust fan (450 cfm), with a dimmer switch, blowing outside. I need stealth because I have a child who I would rather not know about my grow room and, around here, thieves breaking in and stealing plants, equipment, etc are a very real threat. The only place I could see to vent the room discreetly was out the back wall behind a giant bush/shrub. But, even with the switch turned right down, the fan makes a humming sound that is clearly audible when near that corner of the house outside. And with it on full speed, the roar can be heard from the street at the front of the house!

My first attempt at reducing the noise was to build a box insulated with layers of both blue styrofoam insulation and noise-reducing pink fiberglass insulation and fit it around the vent. That helped, but not enough. Last night, I built a second insulated box to put over the first, thinking that might do the trick, but it was very disappointing -- did not make a bit of difference to the sound. Obviously these boxes have to be open at the bottom for the air to blow out and I`m guessing that is why I`m not getting good results.

I have a couple of 90w UFO LEDs which don`t give off much heat, but the big problem is my 1000w HPS and as you know, those are HOT! Even though I`ve now got the HPS in a CoolTube, which has helped quite a bit with the heat problem, the temp is still in the 88 degree range when the lights are on.

I need to turn up the fan, but I can`t unless I can come up with a way to quieten it. I used resilient channeling and sound-reducing insulation when I built the wall to partition the new grow room from the laundry room and that worked well -- can`t hear the exhaust fan or other fans in the rest of the house (faintly when standing right outside the door). But outside is a problem!

Is there any point in cutting a bigger vent hole in the exterior wall for the exhaust fan and cushioning the fan with something that would absorb any vibrations (I`m thinking a `pool noodle` might actually work well, wrapped around the edge of the hole)? I`m not sure how much of the sound is rushing air and how much is the sound of the motor/fan-housing vibrating.

So far, I`ve been masking the sound by turning the clothes dryer on whenever anyone is around outside (the dryer vent is about 8 ft away from the grow room vent), but this is obviously not a good long-term solution!

Incidentally, the fan is mounted to the exterior wall (actually, the interior wall of the two-layer exterior wall - hopefully you follow me!) that it is blowing through. Would it help to move the fan further inside the grow room and have a longer pipe/vent-hose between the fan and the vent to the outside?

Does anyone have any other suggestions?

(BTW, I can`t afford to buy another fan & vortex is the only brand available where I live, & I`m not a fan of ordering this kind of thing over the internet... no pun intended :P )

Thanks!

-Lee