Carbon Filter Question

I am growing in a closed environment. The room was air-tight. During the day hours, my CO2 levels run between 1100 and 1200 ppm. At night, they run the same. This is a problem. My plants take a noticeable hit after 2-3 days.

My solution was to install a vent fan for the night hours. The vent fan is attached to a carbon filter (for smell). The fan is a 6" inline, that feeds into 4" ducting. I drilled a 4" hole in the wall and secured a washer/dryer vent hood to the outside of the room/ attached the hose on the fan to the tail end of the hood. The idea is that at night, the fan will turn on, pull air through the carbon filter, and pass that air out of the grow room. The carbon filter is vertical with the fan on top (and the setup is on the floor because CO2 weighs more than air).

Here is my problem: even with the fan off, there is air being pushed out of my grow room (evidenced by the flaps on the vent hood).
Any suggestions to solve this problem?

Much thanks in advance.

a backdraft damper should solve that

slowbus said:

a backdraft damper should solve that

Click to expand...

I think you misunderstand what he is saying.... or I am.

hey op are you saying that even when the fan is off that the flapper on the exhaust hood/dryer flapper is still opening? AS in your room has pressure on it somehow?

Have you checked the open vent outside for air flow??
Or is the flap stuck... New flaps tend to stick
(usually sucks more in the beginning and end of summer when bees and hornets fly in....)

You have fans running in the space for circulation, this is all it takes to produce enough positive pressure to create a bit of flow, even through a filter, as long as it is passing through the filter, I would not sweat it. it is hard to have a room 100% air tight, and not really needed, and as you can see, has drawbacks. Everything that is alive, breathes, your grow environment is no different. I have also read a bit that a couple of "cycles" of C02 had equal and or better results than a constant CO2 during lights on and is cheaper in the long run, so the ppms dropping a bit during lights on is ok.

I have a very tight room as well, 100% light tight, but nowhere near 100% air tight, but if you are in there and pull the door closed a bit quick, it will box your ears for sure and makes all the ductwork jump. All the air that leaves passes through a filter. I have several small (circ) fans in my room and it is more than enough to open a cloth backdraft damper through a 4x18 filter.

Hope this helps.

Peace and Great Grows

Asmallvoice

Thanks so much all for the responses!

@slowbus, Joe Macclennan has the right idea. Even with the fan off, the air pressure in the room is enough to push air out through the vent. I have been looking at dampers, but the way I figure, unless a damper is rated to open only when say, 450 cfm is applied, then a damper will be pretty much useless (i.e. it will still keep open when the lights are on and the exhaust fan is off).

@Mr. Ganja, this is very helpful information. Much thanks. And you're correct: I do have fans running inside the room, as well as A/C, so there is pressure in the room to push air out. My CO2 is digital, so it maintains the room at 1100 to 1200 ppm. From what you're saying, though, I'm not losing significant amounts of CO2 during the day hours through the vent. This is a definite relief!