C02... but with an intake fan... hmm

I'm building a new cab in a month or so. I have my lighting, exhaust, intake.. basically everything figured out. But I also have a C02 system that I want to employ, but I'm running in to a problem.

My intake fans are two 5" Axial fans (basically bigass computer fans). I want to mount them down low, on the opposite side of the cab as the exhaust. I will set them and the exhaust fan to come on twice and hour and exchange all the air in the cabinet. When the fans are off, I will pump C02 in to the cab (it's a small cab, so getting it to 1500ppm will be quick and easy). However, I cannot think of a way to keep the C02 from escaping through the intake fans. I have shrouds over the fans on the outside of the cabinet to keep light from escaping or getting in, but it's light tight... not air tight.

Does anybody here have a solution for keeping their cabinet air tight when all their fans are off?

Any help is greatly appreciated.

You want a flapper valve. Or a spring loaded butterfly. A flapper would be best for you since your system is low pressure.

Just take a piece of cardboard or hard plastic and cut it to the size of the fan opening, then take a strip of tape and tape it to the top of the opening. Than ass a little weight, to make sure the flap goes down when the fan is off. You will have to experiment with the weight so that the flap shuts but the weight does not hinder your fan. The moving air from the fan should lift the flap, and too much weight will constrict air flow. I recommended adding some window sealing foam around where the flap seats for a better seal. This will not be air tight, it will leak a little, but for your purpose it will work, the flap will stop most of the air flow inside or outside the box.

Home depot has a dryer vent that is very similar to what I described, except it contains many little plastic flaps. I have seen them in 3, 4, and 5 inch.

Good luck
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