Hydroponic Garden Ventilation

Why is hydroponic ventilation necessary?

To maintain adequate hydroponic grow room ventilation, grow room fans can be used to control humidity, temperature, and carbon dioxide levels. A grow room fan or hydro fan within a grow room is essential for a number of reasons.

By exchanging, circulating and mixing the air, a hydroponic ventilation will give you more control over the following growing conditions.


Inadequate ventilation can lead to high humidity and this can result in a number of problems for the plant at various stages of growth. A humidity of 60% RH (Relative humidity) is recommended during vegetative growth and around 40% RH during flowering to prevent flowers or fruits from rotting.

HYdroponic ventilation will also help to prevent fungal diseases as fungal spores thrive in humid, stagnant air. Stale stagnant air also provides other airborne pests such as sciarid flies a greater opportunity to infest your grow room.

Hot air holds more water vapor so by extracting hot and humid air and replacing it with cooler less humid air, high humidity will become less of an issue.

Carbon Dioxide

Plants need carbon dioxide (CO2) to grow and photosynthesize and this is essential for plant growth. Plants within any confined space will soon use up that carbon dioxide.

Therefore, a hydroponic extraction fan is necessary to maintain high levels of carbon dioxide and ensure a fresh supply of air into the grow room. We recommended that you try to replace the air in your grow room at least 20 times per hour or every 3 minutes to maintain a reasonable air quality.


Hydroponic lights within a grow room can produce a lot of heat. When the lights are on the temperature should range between 21 to 28 degrees centigrade (70 to 82 Fahrenheit). Try and reduce this temperature by about 5 degrees Celsius (9 degrees Fahrenheit) at night as this is important for correct flower maturation.

Grow room ventilation using a hydro fan will help maintain the correct temperature. A hydroponic fan speed controller will enable greater control of the temperature as they can be controlled by a thermostat.

A fan speed controller linked to a thermostat will enable you to vary the speed of the hydroponic fan automatically depending on your preferred air temperature.

Hydroponic Fans

Good hydroponic ventilation is essential for healthy plant growth. It is one of the most important factors to consider when growing plants within an enclosed space. Ventilating a grow room or grow tent involves selecting the correct size exhaust fan or extractor fan and maintaining a fresh supply of air from outside.

We created this section of our guide to help you choose the correct hydroponic fan for your grow room. We also provide guidances on the best setup and recommended method for installing a hydroponic fan.

What Size Fan Should I Buy?

Buying an adequate sized fan for your grow area is important as the cost of a hydroponic fan will largely depend on its size and power. Generally speaking the longer the length of the fan the greater the volume of air that can be extracted at any given minute.

However, fan designs can vary significantly and you will want to know the Cubic Feet per Minute (CFM) value of the fan. CFM specifies the volume of air in cubic feet extracted every minute.

Firstly calculate the area of your grow room or grow tent. Multiply the room’s length by the width by the height. So for example for a 7 foot by 6 foot by 10-foot area, the volume would be 7 x 6 x 10 = 420.

The extraction fan/exhaust fan should exchange the air in the room at least once every three minutes. So simply divide the area in cubic feet by three minutes to calculate the minimum CFM: 420 / 3 = 140 CFM

If you plan to use a carbon air filter (more on that later) multiply by 30%: 140 x 1.3 = 182 CFM.

This is minimum recommended air flow rate and once this has been established you should buy a hydroponic fan with a similar air flow rate.

Vent Hole Size

The grow room must include a vent hole to draw air into the room while the hydroponic extractor fan is drawing air out. The vent hole needs to be at least the same size as the size of the extractor. For example, if you are using a 7-inch extractor, the size of the inlet hole should be at least 7 inches but preferably slightly larger to reduce drag.

Also, air drawn in through the inlet hole needs to be near to the ground were as the extractor fan drawing air out needs to be positioned near the top of the grow room or tent. This will enable better air circulation and mixing and also remove the hot air that tends to rise.

Intake and Extractor Fans

An intake fan can be used in conjunction with an extraction fan to pull air out of the grow area. An intake fan is the same as an extraction fan. However, it is used to pull air into a grow room instead of removing air. The extractor fan should be positioned at the top and preferably on the opposite side of the intake fan.

Whether you use an inlet hole or an intake fan, the important thing to remember is that the fan pulls fresh air from outside.

If you chose to use both intake and extractor fans, the combined CFM of both fans must total to the required CFM. Therefore, if you require 182 CFM, one fan could be 140 and the other 42. However, the intake fan should always have a lower CFM. It should preferably be a third to a half of the extractor fan.

Having two fans working together provides better control of humidity and temperature; it creates negative air pressure within the room and prevents smells from escaping back through the ventilation system. You will also discover that the fans will be less noisy and last longer.

Sometimes you have to move air to an exterior vent or move air a distance from an outside wall. If so, you may need to use ducting. Ducting comes in standard sizes that should fit all of your fans and filters. Flexible ducting is easier to work with, but it is important to try and keep it straight.

Your ducting should be as short and straight as possible. You should try and avoid bends in the ducting. These bends will create drag that in turn creates noise as the air moves through. It will also lower the efficiency of the grow room fans and may require more powerful fans to compensate.

Buying a Carbon Filter

If the exhaust from your grow room smells you can do something about it. You can use a hydroponic carbon filter with your grow room extractor fan. Carbon filters, also known as carbon scrubbers, will remove almost all of the odor from the air before extraction. You should replace or refill carbon filters periodically.

Normally you would have a setup like the following. You place the fan and filter inside the grow room or grow ten. The fan draws the air through the filter before leaving through some ducting to the outside.

If the growing area is too small you can get away with placing the hydroponic ventilation fan and filter outside. This frees up space inside the grow room.

This way, the extraction fan pulls stale air out of the grow room through some ducting. Since the fan is located outside, the air if pulled through it and through more ducting. The fan also pulls the air through the filter during extraction.

Other Accessories

Fan speed controller: A fan speed controller controls the speed of the fan. If the fan speed controller uses a thermostat to regulate the temperature of the grow area. This is more efficient, reduces noise and prevents the temperature and humidity from being too high or low.

Acoustic ducting: If the fans are too loud you can use acoustic ducting to reduce the air turbulence noise. Fix a silencer on each end of your fan to get the full benefits.

Hydroponic Guide Sections

To learn more about other aspects of hydroponic gardening, see the following sections of our guide.