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STOP Odours Escaping! Eliminate Grow Room Smells

STOP Odours Escaping! Eliminate Grow Room Smells

Alex Grady

Grow rooms can smell pretty funky! You don’t want any tell-tale odours escaping your tent or home.

Odour control is key.

To get their aroma, plants release volatile organic compounds (VOCs) into the air. The good news is these can be removed.

Here are 6 things you should do.

1. Carbon Filters / Carbon Scrubbers

By far the best way to remove odours is with a carbon filter. They literally ‘scrub’ plant smells out of the air before it’s extracted.

For this reason, carbon filters should be part of every ventilation system.

Air in >>>>> [carbon filter > clamp > extractor fan > clip > ducting] >>>>> Air out

Your extractor fan pulls air through your carbon filter. As this happens, air passes a bed of activated carbon. The VOCs that cause plant smells get trapped inside the pores of the activated carbon – they are adsorbed.

The trick is to make sure you get the right carbon filter.

Here’s what you should look out for:

Carbon Bed

The deeper the carbon bed, the more activated carbon there is. Filters with deeper beds tend to last longer.

Spigot Size

To ensure your fan and filter can be connected, match your spigot size to the diameter of your fan. If they don’t match, you can use a reducer. BUT the chances are if your carbon filter spigot is too small, it’s not suitable for the air flow of your fan.

Air Flow

Air needs to be in contact with the carbon in your filter long enough to remove odours. To make sure this happens, the air flow rate of your carbon filter and fan need to match.

Don’t forget to maintain your filters. It’s important that you:

  • Replace pre-filter / carbon filter sleeves
    Pre-filters and filter sleeves stop dust getting into your carbon filter - dust that would otherwise reduce the life of your carbon. To keep dust out, you’ll need to replace them every 3 – 6 months.
  • Replace carbon filters when needed
    This will normally be every 9 months - 2 years, depending on which filter you buy.
  • Do not humidify with unfiltered water
    Unfiltered water contains minerals. When used in a humidifier, these minerals can clog up carbon filters and reduce their life. To prevent this, always use RO water with your humidifiers.

2. Draw In Less Air Than You Extract

You should draw in 20% less air than you extract to maintain negative pressure.

Unless you do this, your tent could overfill with air. Smelly, unfiltered air can start seeping out of zips, corners and joins before it has been through your carbon filter.

You can use an Expando Grow Tent Maximiser to stop your tent walls getting sucked in by fans while maintaining negative pressure.

3. Ozone Generators

Like carbon filters, Ozone generators remove odours, rather than masking them. Only they do it via oxidation.

Ozone (O3) is 3 oxygen atoms bonded together. It's like the oxygen we breathe (O2) with an extra oxygen atom.

Oxygen we breathe = O2

Ozone = O3

The thing about oxygen atoms is that they like to exist in bonded pairs. So the extra oxygen atom in Ozone is very unstable. It easily breaks off and binds to organic molecules – like the VOCs that cause plant smells. When this happens, the smells become oxidised and the smell is eliminated.

There are two ways to use Ozone generators:


These sit in your ventilation system. You should use them alongside your carbon filter. They add an extra layer of security to ensure all odours are removed before you extract air.


These emit small amounts of Ozone directly into your grow room.

4. ONA (Odour Neutralisers)

ONA blocks, gels & sprays are the best neutralisers to use outside your growing area.

They’re so good at neutralising odours that sewage treatment plants use them.


VOCs are attracted to, enter and bond with ONA’s active ingredients.


VOC molecules that cause plant smells are held on the surface of ONA molecules.

Chemical Reaction (The Pairs Theory2)

When two odours are permanently bonded, they can cancel each other out. This is what happens with VOCs and ONA active ingredients.

Just remember not to use ONA in your growing area. They’re so good they can affect the taste and aroma of your final harvest.

Lots of growers use ONA blocks, gels & sprays in the room their tent is in. You can also get blocks that sit in your ducting.

We recommend using an ONA Spray Card to neutralise smells that cling to clothes.

5. Watch Your Heat And Humidity In Flowering

VOC production is highest in flowering. It’s ramped up even more when your heat & humidity are high.

Your humidity should be low in flowering anyway, to prevent bud rot and mould.

It’s also a good idea to use air circulation fans to make sure you don’t get hot, humid spots around plants.

If you do get temperature problems, there’s a lot you can do. For example, you can swap to cooler grow lights, like a Telos LED.

6. Cool Lights Using Air From Outside Your Tent

Some growers push air from inside their tent over air-cooled lights.

Bad idea.

Air from inside your tent is smelly and is full of plant debris that dirties your reflectors.

You’re best off using air from outside your tent for air cooled lights for 3 reasons:

  • No plant smells to remove before venting air outside
  • Reflectors stay cleaner for longer
  • The air is cooler so is better at removing heat

In Summary

The best way to remove odours is with a carbon filter. Nothing else works as well. Never, ever, ever extract any air before it has been through a carbon filter.

If you’re still getting lingering smells, you can remove these with:

  • Ozone generators
  • ONA blocks, gels & sprays

If that’s still not doing it, try reducing the heat and humidity around plants in flowering. That way there will be fewer VOCs to remove.

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