Double filter

This is aimed more at stealth growers.

I'm growing in a closet in a gorilla tent. I am using a correct if not oversized fan and phresh filter. I only use a filter for two grows and replace it. Don't let the humidity get to high and during drying push upper 60's with humidifiers for a few days max.

I vent thru the access hatch into the attic and have never smelled anything out doors. However when we are getting late in flower and they smell the strongest I can smell a very slight trace in my garage at the other end of the house when the garage door has been shut for a couple hours or more. It dissipates quickly when I open the door. I doubt it's from the closet because with the tent sealed and closet shut I can't smell anything at all inside until I open the tent for tending plants. Then the whole house smells in minutes. To be expected and as soon as I close the tent and closet door the smell is gone within 10-15 minutes in the house.

Does anyone "double filter"?

I'm thinking of adding another filter where the duct goes into the attic on top. Plus the one on the inlet of the fan. The total length of the run is 6-8 feet at most including the fan. Inlet fan pulls air and exhaust side fan pushes thru which shouldn't matter.

do you have it set up like this?

filter>fan>ducting>attic

Speed of green said:

do you have it set up like this?

filter>fan>ducting>attic

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Worth a thousand words eh? Tent is only 2' deep by 30" wide but we are not growing for more than us and a little friending. Its why I cant cant do clones or waste time on non fem seeds. Did that first grow and it cost me all of veg to find a couple drag queens hiding in my closet.




This the typical access to the attic in many homes. I replaced the insulated hatch with a plywood replacement with the hole and added 6" of insulation to the top. The stack extends about 20 " up and its capped with a mesh screen door material just in case bugs try to flow back down if the fan were off.

I have one 8'' phresh fan into inline phresh filter short ducting to floor into phresh 8'' filter. works well ,lot quieter n running flat out.

noyd666 said:

I have one 8'' phresh fan into inline phresh filter short ducting to floor into phresh 8'' filter. works well ,lot quieter n running flat out.

Click to expand...

So is that two filters if I read that right? Noise is not an issue. The S&P fan is quiet, the oscillating fan makes more noise. Its the telltale small level of odor in the garage that has to be seeping thru the filter when the smell gets to this point. Considering how when I open the tent the smell is like a wall of heaven I just dont need it outside. My clothes smell just from leaning in to water. Its a 2 speed fan and it does not seem to make a diff if its on high or low for smell.

So the issue is that the filter cannot keep up with the smell, there is positive pressure after the fan so no odor could enter the ducting after the fan.

Since you mentioned that there is no difference in odor control regardless of fan speed.

the simplest solution for now would probably be to add another filter in the attic.

While this will fix the symptom the problem is probably that your fan is oversized for the filter.

When exhausting odor through a carbon filter you only get one shot at trying to remove 100% of the odor, if the fan is too strong the reaction time with the carbon filter lessens and some odor escapes. it makes sense that you have only run into this issue when the smell is stronger.

a more permanent solution would be to look at a fan speed controller to slow it down, you should be shooting for about 125cfm max & look for an exhaust rating on your carbon filter.

carbon filters are extremely effective, and since yours is new and ducted correctly, this is the only other variable besides very high RH.


hope this helps