How to Use a Carbon Filter in Your Duct Fan

When growing plants in an enclosed space, it’s important to maintain good air quality to keep odors to a minimum and ensure that your plants are clear of mold and other pathogens. Whether you decide to DIY or hire a local pro for help, learning how to use a carbon filter in your duct fan can improve the air quality in your home.

Why Use a Carbon Filter in a Duct Fan

If you grow a lot of plants indoors, a carbon filter can help eliminate pollen odors and reduce mold spores. Plants tend to be healthier overall in a space with good air quality, and you can expect higher yields from healthier plants.

Carbon filters can benefit homeowners without a green thumb, too. Adding a carbon filter to your air system helps remove household odors, pet dander, allergens, and pollutants. 

How Much Does It Cost to Install a Carbon Filter in a Duct Fan?

In most cases, installing a carbon filter for a duct fan will cost between $120 and $200, depending on the size of your fan. Replacing an existing filter costs between $10 and $50.

How to Install a Carbon Filter in a Duct Fan

Improving air quality and minimizing odors in an indoor hydroponic or tented grow space can be tough. Here’s how to use a carbon filter in line with a duct fan to circulate and clean the air.

1. Size Your Fan and Filter

The first step in installing a carbon filter is deciding what size filter you need. Filter size is measured in cubic feet per minute (CFM). While we recommend consulting an HVAC technician for their recommendation, it’s easy to figure out the right CFM yourself with a little math. 

1. Calculate the cubic footage of the room by multiplying its length, width, and height. For example, a room that measures 10 x 12 x 8 has 960 cubic feet. 

2. Divide the room’s cubic footage by the frequency (in minutes) that you want the air to be exchanged. The recommended air turnover rate is every 1 to 3 minutes, with 3 minutes being the most common. This means you would divide 960 cubic feet by three, which equals 320.

3. Purchase a carbon filter with a corresponding CFM. In the example we used, you would purchase a filter with a CFM of 320.

Below, we’ve laid out several CFM recommendations based on different room sizes.

2. Choose a Spot for Your Filter

Place your carbon filter as close to the source of any odors as possible. Positioning the filter at the top-center of your plant growing space will allow it to collect particles before they can spread throughout your space.

3. Run Your Ducting

Your carbon filter must be ducted to ensure proper ventilation and air purification. This can be done a couple of different ways, and it varies widely in complexity.

Most often, a carbon filter is connected to an exposed exhaust fan and set up in a grow tent. This is the easiest option because all parts are accessible by hand. To install, simply connect the carbon filter to a fan and run ductwork from the fan through a vent in the tent. Just make sure the carbon filter and the fan have the same diameter ahead of time; that way you know the ductwork fits both parts.

If you plan to connect a carbon filter to an inline duct fan, the process is more complicated. For this, we recommend hiring a professional because it requires cutting ductwork by hand and running it directly to your HVAC system. 

4. Attach Your Filter

Ensure your filter is properly sealed to the ductwork, or you won’t see any benefits. To achieve a tight seal, consider two attachment methods.

Foil Tape

Join your carbon filter with your duct using metal foil ducting tape. Wrap the tape continuously around the joint and overlap the ends by at least one inch to ensure an airtight seal.

Hose Clamps

Measure your duct fan opening and select a clamp with the same diameter. Tighten the hose clamp with a flathead screwdriver to prevent air leaks.

5. Check for Leaks

Once installed, turn on the fan. If you notice any air moving around the joints, you may need to redo your tape or tighten your hose clamps to seal up the system and keep the air moving through the filter.

Duct Fan With Carbon Filter Maintenance

Here are a few tips for maintaining your carbon filter duct fan to ensure peak performance.

• Keep the humidity down: Although some plants thrive in a humid environment, a carbon filter loses effectiveness above 80% humidity. Monitor the moisture in the air to keep your carbon filter working well.

• Replace filter annually: Although filters can last up to 18 months, if you use the fan regularly, replace your filter annually.

• Clear vent covers: Ensure the opening is clear of leaves and check intake vents to ensure that they aren’t sucking in larger debris. 

• Clean your fan: Switch off, unplug, and wipe down your fan blades every time you change the filter or more often if you notice a build-up of dust or dirt. 

• Check the filter regularly: If you notice more odor than usual or see any damage to the filter or the seal around it, it’s likely time for a replacement.

DIY vs. Hiring a Pro

Installing a carbon filter can be a simple DIY that saves you $50 to $300 in labor. The DIY costs are low since this project only requires a screwdriver and some tape. However, if there is any damage to your ductwork, like cracks, holes, or water leaks, hire a local duct installer. They can conduct a full inspection and resolve any issues before they become a larger problem.