There is no shortage of carbon scrubbing exhaust filters for cannabis growers. Even the most basic grow setups typically have a carbon scrubber to eliminate exhaust smell.

For some reason, air intake filters are an afterthought in most grow space designs. I think this is because intake filters are difficult to incorporate into grow tents that do not have the same type of airtight seal a rigid plywood grow-box does. As we enter an era of legalization the air intake filter should become more important than the carbon-scrubbing exhaust filter that was designed to hide smells during the prohibition.

Air intake filters remove pollen, mold spores and dust mites. They will even filter bacteria (if you buy a filter with an MER of 13+). I recommend a filter with a MERV of 8 or more (MPR 600+) to filter out mold spores.

In my initial design, I used a waffle style filter that you find in most living room air purifiers.

This worked well but these filters are expensive and even in a small 2 plant 240 Watt grow I found it to be too restrictive on airflow. I upgraded to furnace filters which are actually cheaper, I guess due to mass production. On Amazon and Costco you can readily find them for under $10 each. Get a filter with an MER of 8+ in order to properly filter out mold spores.

I decided to make a frame around the furnace filter for easy removal and so that I could add some light-blocking shutters. This is entirely optional as you could just tape the filter on to the side of your box for installation.

My grow box has ambient light around it 24/7 so for good measure I installed light blocking shutters. If you are worried about light leaks you could also get a thicker filter. The filter above is 1″ thick but you can get them up to 4″ thick.

Remember this is why we use air intake filters. Buds are sticky and this dust would otherwise have been stuck in your precious nugs!

I have applied this same idea to many types of grow spaces.

Air Filter Micron Levels Explained: