For indoor gardening it is necessary to have adequate ventilation this is especially important if you are using high intensity discharge lighting. 

Ventilation really consists of three main parts.

  • Intake 
  • Exhaust
  • Circulation 

    The intake does not have to necessarily be a fan typically it can be a hole or an opening either outside or into a cool space.  The intake has to be one size larger than your exhaust meaning if you have an 8″ exhaust fan you need an 10″ intake.

    The exhaust fan should be matched to the number of lights you have running,  a standard rule of thumb is every 1000watt HID light produces 150 to 250cfm worth of heat load. this formula is based upon the indoor growing situation being in a normally cool space, in this situation 150cfm will do.  Now say your indoor garden is in an attic for this situation you will need 250cfm per 1000watt light at least. 

    Circulation fans are a must have to keep the air in the room moving,  if there is no air movement in the room the plants will deplete the air directly around the leaves and this retards growth.  it is also VERY important not to have the fans blowing directly on the plants especially at a young age this will cause the young plant to transpire all its moisture away, this dries out the leaves and stunts its growth.


There are several different options when it comes to ducting 

  • Clear flexible Ducting: is very cost effective and will work for most applications because it is clear light will shine through it,  Clear Ducting CANNOT be used with ozone as it will deteriorate.
  • Mylar flexible Ducting: This is one of the most popular it is durable, long lasting, non see through, and can handle heat and ozone. 
  • Insulated flexible Ducting: this is very popular for sound dampening and for reducing condensation.
  • Metal Ducting: this works well for permanent installations but can be problematic when it comes to bending, typically not that common.  

**Most of the flexible ducting comes in 25′ lengths.

**For damping sound with any of the ducting try adding a couple of 90 degree bends, this defuses the airflow cutting down on that jet engine sound at the opposite end of the duct.


    When picking a fan for a indoor garden there are a few key points that you’ll want to keep in mind.  Not all fans are designed to do the same chore, 

  “Squirrel” Cage Blowers are typically used in furnaces, and air conditioners the work well when moving air unrestricted  most of these fans are not terribly efficient or quiet.  Squirrel cage blowers are best suited for use in greenhouse type applications where there is little or no ducting involved, as the cfm of these blowers drops drastically when restricted in the slightest.   The nicest thing about these blowers is there cost  both new and used squirrel cage blowers are dirt cheap and can be used to get by until a better fan can be purchased. 

Inline centrifugal Fans are probably the most efficient fan for any indoor garden.   This is because of there design and the components,  most of these fans are exceedingly efficient, and maintain there cfm through great distances of ducting with very little loss.  Another very nice thing about these fan’s is that they are quiet (for the amount of air they move).  Some of the better inline fans have sealed and hydrophobic grease bearings for use in higher humidity situations.  

These little duct fans were designed to be used inline after a centrifugal fan, to boost airflow after great distances.  They also make great intake fans and come in a variety of sizes. One thing to remember is that the cfm on the box is a free air rating and drops as soon as it is installed inline. 

    Axial Fans are what you would find in computers and photo copy machines they move allot of air and are very quiet.  they range in sizes the most common being 4″ 6″ 10″ axial fans make great intake fans or exhaust fans for a single 1000watt or smaller, depending on the operating temperature of your garden room

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