Urban gardeners can use carbon filters to purify the air in their grow rooms making them free of dust, pollen, foreign particulates, organic compounds, and offensive odors. Filters should be used during the entire grow and matched correctly to an inline fan ducting air outside.

Carbon filters are used anywhere it's important to have purified air. For example, you'll find them used in research labs, schools, hospitals, and of course, indoor gardens. They're even used in people's homes to alleviate allergies.

When choosing a carbon filter, the most important thing to consider is the grade of the carbon. The best filters use granulated carbon which has more surface area than the pelletized type. The result is a filter that requires less carbon and is much lighter.

Carbon filters work by trapping airborne particles in the pores of the activated carbon inside the filter. To accomplish this, you need to draw air through the outside of the filter so it passes through the carbon and then out through the internal exhaust of the filter itself.

One common set-up is to hang the filter horizontally near the top of your grow room since warm air rising in the room often carries the stinkiest particles.

You would run ducting this way: Carbon filter [http://www.pchydro.com/atmosphere-filters-ozone-c-72_65/phresh-filter-14x48-inch-p-4760] > Lights > Fan > Outside. In this way, you'll be air-cooling your lights and scrubbing the air by pulling it outside. Furthermore, you'll be creating negative pressure in the room, keeping the air clean and odorless.

To make this work, you must properly match the sizes of your filter and inline fan. The fan you choose should be able to exchange the air in your grow room in under five minutes. Determine how many cubic feet your room is by multiplying its width x length x height. Once you have this number, divide it by 4. Next, choose a fan and filter that closely matches the number, rounding up.

Once you have everything set up correctly, be sure to replace the charcoal in your filter every four to eight months.