How to Smell Proof a Grow Room

Growers face a common problem; sometimes, growing marijuana doesn’t smell great. Wondering how to smell proof a grow room is normal, especially if you live in a smaller space and your neighbors are complaining.

As legalization spreads and more and more people decide to grow their own marijuana, this problem is only going to become more common.

There’s nothing you can do to prevent those smells. They’re a natural byproduct of growing marijuana. The plants themselves have a distinctive smell, and the fertile soil you need to grow them in can be pungent, too. Fortunately, there are ways to prevent that smell from spreading and annoying your neighbors.

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What Is Causing the Smell?

First, you should know what the smell is. When you smell something, what’s happening is you are inhaling molecules in the air. These molecules land on special scent-receptors in your nose, which then sends a signal to your brain.

Scent molecules are created by all sorts of things, but mostly, they come with volatile organic compounds. That’s the technical term for substances that evaporate easily, which means that the molecules that make up their substance have a lot of energy and are very easily dispersed as vapor in the air.

Every scent you smell, good or bad, is made up of these molecules. The strength of the scent you smell depends on the concentration of the scent molecules in the air. This means that stronger smells are generated by higher concentrations of scent molecules.

Scents You Can’t Smell

Our nose can detect about 10,000 scents. That sounds like a lot, but in fact, it is only a small percentage of all the scents that exist. That’s why dogs can smell so much better than we can; their noses can detect many more scent profiles than ours can.

Insects and other pests are also capable of smelling more scents than we can. In fact, the scents that are most attractive to pests are often ones that humans can’t smell. This means that even if you don’t think your grow room is producing any smells, it almost certainly is, and those smells are probably very attractive to pests.

This is just one more reason to learn how to smell proof a grow room. If pests can’t smell the plants, they won’t go looking for them. In fact, the ability to smell proof the room and easily keep pests out is one of the best things about indoor growing.

What Do the Smells Tell You About Your Plants?

Even if we can’t smell everything, we can smell enough to use our noses more than we do. Growers should be sure they learn everything they can about the way that their plants are supposed to smell.

There are smells that your plants should be giving off. These smells can tell you a lot about the health of your plants.

Once you know how your plants are supposed to smell, you have one more way to determine if something is wrong. If your plants aren’t producing a smell at all, or are producing the wrong smell, you will know that there is some sort of deficiency.

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Other Factors That Affect Smell

Substances that give off smells are affected by the environment. Imagine standing by a full garbage dumpster on a hot day compared to standing near it on a cold day. The dumpster will smell much stronger on a hot day.

With that, you will realize that smells are affected strongly by heat. Hot food is more aromatic than cold food. It’s the reason that wine experts always provide specific temperatures to serve certain wines at; that temperature is where the wine gives off its best aroma. A hot grow room is going to smell much, much stronger than a cooler one.

Water also affects smells. Many scent molecules are water-soluble, which means that we can’t detect them as well when they aren’t mixed with water. Since humidity is a measurement of water vapor in the air, humidity also affects smell.

If there is more water vapor in the air, some things will give off a stronger smell. That includes many plant smells and also includes many of the scents that soil gives off. If your grow room is humid, it will smell stronger. A grow room that’s both hot and humid is going to smell very strong.

how to smell proof a grow room

How to Smell Proof a Room

By now, you should already know that your plants will produce smells that you can detect and smells that you can’t detect. Not only is this unavoidable, but it’s also actually a good thing. This knowledge will help you to gauge the health of your plants.

Then again, that doesn’t solve the problem of upsetting your neighbors with the smell. And, truthfully, you may not want your entire apartment to smell like a marijuana garden either.

Now that we’ve explained the science behind the smell, it’s time to talk about smell-proofing your grow room. There is more than one way to do this effectively, so we’ll cover the best methods and let you decide for yourself which smell-proofing method is best for you.

Using Duct Fans and Carbon Filters

Carbon filters like these are a great tool for purifying the air. These have been used as air and water filters for a long time, and they’re extremely effective.

6 inch carbon filter infograph

Yield Lab 6 Inch Purifier Activated Charcoal Filter

The surface of the activated carbon is so porous that it’s extremely absorbent, and the larger molecules that create smells and impurities are trapped in the carbon.

A carbon filter needs to be paired with a fan such as one of theseĀ  in order to filter the air truly. The fan pulls the air from the room through the filter, and all of the scent molecules get trapped in the filter. This is a very effective setup, but you do need to make sure that you use the right size fan and filter for it to work.

Choosing the Fan and Filter

For most grow rooms, a six-inch fan and filter combo is ideal, but you really want to be absolutely sure before you buy. Filters are rated by the size of the room they can effectively work with, and the number used is in cubic feet.

Essentially, the cubic foot measurement is a representation of the volume of air that a given filter can handle. It is usually abbreviated as CFM or cubic feet per minute. This is not just a measurement of what the filter can handle but also of how much air the fan can move.

To determine the CFM that you need, you need to measure the width, height, and length of your grow room. Multiply these numbers together, and you have the volume of the room. You want to be able to exchange all of the stale air in the room with fresh air every three minutes, so take the volume and divide by three, and you have your CFM.

Other Factors to Consider

In addition to volume, there are other things you need to take into account before buying your fan and filter. For instance, using a filter has an effect on how quickly the fan can circulate the air, and you need to account for it.

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If you are using a carbon filter, add 20% to the CFM you calculated earlier. If you’re using HID grow lights, you need to add another 15% to 20% since the heat they generate will affect the air quality.

Remember, too, that heat and humidity increase the number of scent molecules in the air, which can require more filtering. Heat and humidity in the grow room can require an additional 25% to 40% be added to your CFM.

Once you have all of these factors figured out and you know your CFM, you can set up a duct fan with a carbon filter. This system will smell-proof a room very effectively, and your neighbors will never smell your grow room again.

How to Smell Proof a Grow Room Without Fans

A fan and filter combination is, without doubt, the most effective way to smell-proof your grow room, but it isn’t always an option. If you’re renting an apartment, it may not be possible to install the necessary ducts, fans, and filters. Or, you may simply need an easier option.

Fans can also be very loud, and that is true for even the best of them. That added noise may cancel out the benefit of reducing or eliminating the smell since it could just be replacing one annoyance with another.

In that case, you may want to consider other methods of eliminating the smell. Since smells are just molecules released by the marijuana plants and the soil, eliminating the smell is as simple as absorbing those molecules.

Filters and fans are so effective because they rapidly move lots of air through a filter, which absorbs those molecules in huge quantities. Other methods won’t work as quickly, but they can still be effective.


These gels are designed to attract and trap odor molecules, creating a passive sort of air purification system. They can be very effective, but they work best in small spaces, like this grow tent. You need to be careful with them, though.

Ona Gel 4L Polar Crystal Air Odor Eliminator/Neutralizer Grow Rooms/Tents Fresh Smell Agents

ONA gels can actually absorb the terpenes that give your marijuana its distinctive flavor and smell, which is something you definitely don’t want. To avoid this, place the gel as far from the plants as you can.

A good idea is to place the gels at the place where you want the smell to stop. This could be the door to the grow room or right next to the air vent that pulls air out of the grow room. If you have a small grow room, the ONA gel will work just fine.

Air Purifiers

Like ONA gel, this machine can be useful for small-scale grow rooms. Air purifier units are similar to a carbon filter and fan setup. They draw air through a sieve or a series of sieves, and as they do so, they trap things in the air that you don’t want to breathe in.

Winix 5500-2 Air Purifier with True HEPA, PlasmaWave and Odor Reducing Washable AOC Carbon Filter

While this can be very useful, it is far less effective than a large carbon filter. The sieves in these are more like the air filter you use for an air conditioner than the carbon filters we discussed above. They will remove some odor from the air, but they will struggle to remove the terpenes that give the plants their distinctive smell.

Air purifiers are only effective in small spaces, too. A combination of ONA gel and an air purifier might be a good way to go if you have a small grow room. It could also be ideal as a way of temporarily improving the smell while you save up for fans and a carbon filter.

The best way to use air purifiers and ONA gel is to place them on the window sills and by the doors to the grow room. This way, they’ll absorb the scent molecules in the air before it leaves the room, but you won’t have to worry about them affecting the plants themselves.

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While there are ways to smell proof a room without fans and a carbon filter, there is no question that a carbon filter is the best way to do it. Carbon filters and fans can be set up to filter the air for any size of grow room, and they will simply do a much better job of actually removing the smells from the air.

Carbon’s ability to filter air is very well understood and widely used, so this should come as no surprise. What is surprising is that it really doesn’t take much time or money to set up an air filtration system for your grow room that will effectively smell-proof it. If you invest in a good carbon filter and fan, and it is a pretty modest investment, your neighbors will never smell your grow room again.

Still, not everyone can or wants to use fans and carbon filters. If you have a smaller grow room, they might even be overkill. In such situations, ONA gel and/or an air purifier can do the job nicely. Just be sure not to place them too close to the plants.

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