How to make an air intake filter for grow tents or grow rooms

It’s very important that you filter incoming air that’s being introduced into your grow tent or grow room. We’ll show you a few cheap ways to filter incoming air to keep dust and pests away from your weed plants.

Why is filtering your air intake important?

If you’re growing weed in a tent or grow room, you need to constantly exhaust air to replenish carbon dioxide and remove excess heat and humidity (unless you’re using a completely sealed room in which you provide air conditioning and supplemental CO2).

When stale air gets pulled out of your tent/room, incoming air needs to be introduced. This can be done passively through an open vent or tent window, or actively using a fan to force in fresh air. To keep your buds free of unwanted bugs and dust, it’s necessary to filter this incoming air.

This is especially true if you’re pushing air through an air-cooled light fixture. If you let dust collect inside the glass below your bulb it will reduce the amount of light reaching your plants, lowering yield.

To prevent this from happening, below are a few different low-cost ways you to filter incoming air.

How to make a fabric filter for your grow tent’s air intake vent

Most grow tents come with screened panels towards the bottom that can open up to allow fresh air into your tent. If you have a fan and carbon filter placed inside at the top of your tent and are sucking warm air out, you can simply open the lower vents to let fresh air in.

The easiest solution to filter air for these vents is to buy a large sheet of filter fabric, cut it to the size of the vent, then use Gorilla Tape around the edges to secure it into place.  You can also use duct tape or aluminum tape, but those don’t typically stick to the sides of grow tents as well as the Gorilla Tape will so you’ll have to check frequently for peeling.

I like to use sheets or rolls of fabric filters, they’re easy to cut and are gentle on your hands so they’re easy to work with. I’ve also tried using some of the fiberglass filter material on cardboard-wrapped air filters from Home Depot.  Fiberglass filters are not recommended: they tend to cut your hands and they also may result in loose fiberglass fibers landing on your plants.

A light-proof solution to introduce clean air in tents

If you’re in the vegetative stage you don’t need to worry about keeping your plants light-proof, so using your tent’s vents isn’t an issue.

But if you’re flowering, you’ll need to make your tent light-proof to ensure 12 hours per day of uninterrupted darkness. So using the tent’s vent flap isn’t an option unless the tent itself is located in a completely dark room.

When I flip to flower in a tent, I’ll close the vent (they usually attach with velcro) and then use black Gorilla tape to tape around the open sides to ensure no light leaks where the velcro attaches. It’s also good to check for other small light leaks around seams and tape those as well with black tape, just to be safe.

I like to use a 6″ aluminum flexible duct tube as my air intake for grow tents.  You’ll need about 10 feet of ducting ideally, but you can get away with less in a pinch if that’s all you have.

Most tents have a few openings on the sides for ducting, and if yours has one towards the bottom that will work perfectly. Just stick the duct into the opening about 6 inches or so and pull the ropes around it tightly to block light.

Since aluminum reflects light, I like to loop the ducting in a small spiral outside the tent to avoid having a straight path for the light to carry through it.  Pointing the open end towards a dark area (such as behind tent) is helpful too. You never want to let light enter so carefully check that when your grow light is running that you can’t see any light escaping the end of the flexible tubing – if light can get out, then light can get in.

If your opening is at the top of your tent, just run the ducting inside the tent so it hangs about a foot from the bottom. That way the cooler incoming cold air will enter down there, and as the hotter air rises to the top the exhaust fan can pull it out.  This provides a nice circulation that wouldn’t occur as evenly if the incoming air came in at the top near the exhaust fan.

How to make a filter to cover a flexible aluminum duct

Method 1: Flat air filter

There are a few ways you can make a do-it-yourself duct filter. The simplest way is to:

  1. Cut a small circle of the fabric filter that’s about 3/4″ larger on each side than the width of the ducting you’re using.
  2. Use duct tape to secure that filter to the sides of the aluminum ducting.

This method is very easy to do, but the filter surface area is only going to be the width of the ducting tube’s opening. It will get dirty pretty quickly, and you probably should inspect it frequently and plan to change this at least once every 2 months, or more frequently if it looks dirty.  Dirty filters don’t allow as much air to pass through.

You can use this approach if you’re using a fan to push in fresh air through the flexible ducting. If you’re using a fan you’ll find that the filter may get dirty quicker, reducing air flow and often increasing fan noise.

It’s better to use plain duct tape instead of the more adhesive Gorilla Tape to attach the filter to the flexible ducting, since you’ll need to eventually peel the tape and replace the filter when it’s dirty. Gorilla Tape is a bit harder to pull off and you may damage the thin aluminum ducting if you’re not careful.

Method 2: Cone-shaped air filter

If you’re able to increase the surface area where the air passes through your filter you’ll increase the effectiveness and lifespan of your filter. Rather than use piece of fabric filter that is barely larger than the duct’s opening and sits flat across it, you can make a larger cone-shaped filter that points out from the duct end.

To make a cone-shaped filter:

  1. Cut a circle of fabric filter that is about 2x the size of the ducting you’re using.
  2. Fold the circle in half, and then fold that in half so it looks like a slice of pizza.
  3. Peel back one layer of the rounded end and form it into a cone hat shape.
  4. Attached to the flexible duct tubing with duct tape.

If you have the available fabric, go with the cone shape for improved performance.  You could also buy a filter from the hydro store that is made specifically to filter incoming air ducts, but they’re expensive.

Note: this filter will NOT filter out pollen from male marijuana plants. So if your grow tent is located in proximity to places where male plants may potentially release pollen, you’ll need to avoid pulling in this air or you’ll risk fertilizing your female plants which will then produce seeds. Yuck.

Summary

Air filters for grow tent intake ducts can be easily made with sheets of fabric vent filter cut to size.  While both the flat and cone methods work to filter air, using the cone-shaped filter is the best bet to ensure good air flow once dust starts to collect.

Avoid fiberglass filters if possible, they can cut your hands and – even worse – they can introduce small fiberglass shards that you most definitely do not want to smoke.

Attach your filters to grow tent air intake panels during vegetation, and use flexible ducting to create a light-proof intake during flower.

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How to make an air intake filter for grow tents or grow rooms
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Looking to filter air intake for your grow tent or grow room? We'll show you ways to filter incoming air to keep dust & pests away from your weed plants.
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Happy Pot Farmer
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