How to Control Grow Room Smell: Carbon Filters, Ozone and Odor Neutralizers

The most effective way to control grow room smell is an activated carbon filter sized to your exhaust fan, backed up by humidity control and, in bigger grows, a duct-mounted ozone generator. Odor neutralizers and masking products handle whatever leaks into nearby rooms. Flowering cannabis throws off a powerful, unmistakable aroma that can draw unwanted attention and bug your neighbors or roommates.

The good news: there are plenty of proven strategies to keep that smell in check. Between carbon filters, proper ventilation and even picking less pungent strains, you can keep your grow discreet and your place free of skunky clouds.

How to get rid of weed smell in an indoor grow

Staying low-key is one of the biggest challenges of growing indoors, and nothing gives a grow away faster than that signature cannabis smell.

During veg, plants don't put out much smell, but once they hit flower they start releasing an intense, penetrating aroma that only gets stronger as the weeks go by. Luckily, there are several odor control methods and systems that'll help you keep the funk contained. Here's how to stop your indoor grow from stinking up the place.

Odor control systems

If you want your grow to stay discreet, odor control isn't optional. The single most essential piece of gear is the carbon filter, aka an activated carbon filter. It's a must for any indoor grow because it scrubs the air you're exhausting and keeps the smell from escaping outside.

Activated carbon filters

Carbon filters are the backbone of keeping weed smell out of a room. They're packed with small granules of activated carbon that trap odor molecules as air passes through. How well a filter works depends on its quality and how you use it.

Filters stop working once the carbon is saturated, so swap them out according to the manufacturer's recommendations. Refill carbon exists, but replacing the whole filter is the safer bet for performance, and it keeps your warranty intact.

What's the best carbon filter for an indoor grow?

Carbon filters come in different quality tiers, each with its own lifespan. The longest-lasting are Prima Klima Industry, followed by Prima Klima Eco Line and, last, Odorsock. Carbon filters are rated by the airflow they can handle and the diameter of the flange where your exhaust ducting connects.

Your filter needs to handle at least as much airflow as your exhaust fan. For example, if you've got a fan with a 150 mm (6 in) flange moving 425 m³/h (about 250 CFM), you need a carbon filter rated for at least 425 m³/h.

How do I get the most out of my carbon filter for an indoor grow?

For best results, oversize your carbon filter by roughly 30%. If your math says you need a 100 m³/h (about 60 CFM) exhaust fan, get a 130 m³/h (about 75 CFM) filter. Don't pull more air than the filter can clean, or you'll end up blowing weed-scented air straight out the vent.

Heads up: carbon filters don't work well in very humid conditions. Moisture can keep the activated carbon from doing its job. If you shut off your exhaust and humidity spikes, the filter may not scrub the air properly once it kicks back on. To keep humidity in check, run a dehumidifier.

Using ozone generators

In large grows, getting rid of weed smell usually means adding an ozone generator on top of your carbon filters. Ozone effectively destroys the organic molecules behind the plants' smell. But it should never go inside the grow space; it belongs directly in the exhaust duct.

Other ways to hide weed smell

For adjoining rooms and other spaces outside the grow that you also want smell-free, you can use odor neutralizers or masking products. The key is designing your odor control around your grow's specific needs so you don't run into serious problems.

Ozone systems for indoor cannabis grows

Ozone (O3) is a highly reactive molecule made of oxygen atoms that readily react with organic compounds, breaking them apart and wiping out that classic cannabis smell.

Ozone is also effective at killing mold spores and bacteria by destroying their outer layer. But you have to use it right to avoid damaging your plants and the terpenes responsible for your buds' aroma and flavor, and because ozone isn't something you, your family or your pets should be breathing either.

How to use ozone the right way

Don't put an ozone system inside your grow room, unless it's in a duct that vents outdoors. Ozone won't kill your plants, but it can hurt their growth and the quality of your harvest.

The go-to ozone units are the ones designed to install inside exhaust ducting, known as inline or duct ozone generators. Pair them with a carbon filter on the intake side to get the most out of them.

Size the ozone generator to match your exhaust's duct diameter and airflow. Do your homework before you buy, since it's a real investment for your grow. You also need to give the ozone enough space and time to mix with the air and do its thing, which means leaving a long enough run of ducting after the ozone unit.

Odor neutralizers

Odor neutralizers work by latching onto the molecules that cause the smell, surrounding them and effectively deactivating them, while ozone destroys them outright. The best spots for a neutralizer are at air exhaust points or in rooms near the grow that you want to keep smell-free.

The most effective odor neutralizer is The Neutralizer Kit, which also comes in a compact version for tighter spaces, The Neutralizer Compact Kit.

Smell problems can get worse at harvest time, so it's smart to put neutralizers or masking products in the room next to your drying space to keep odors from leaking out.

Odor masking products

Odor maskers don't interact with the smell molecules at all; instead, they put out a stronger scent to cover up the weed. They're easy to place just about anywhere, even inside ducting, and work best in rooms next to your drying area or in smaller grows.

Options include Ona Block, great for air vents and ducting, and Ona Spray, which works instantly when you need to kill a smell fast.