How to Calculate the Size and Air Capacity of the Intake Fan:

As mentioned earlier, a continuous supply of fresh air from outside the growing area must be ensured in the grow room. This can be achieved in several ways

1-Flexible Ducts (Ventilation Ducts)
4-Extraction Fan
3-Carbon Filter
D-Rectangular Ventilation Grille
E-Window Opening
Dark Grey: Grow Box
Light Grey: Room

Implement passive ventilation through which fresh air can be introduced (via an open window).

Note! Generally, passive intake should be 2 to 3 times larger than the extraction output.

This means that if the extractor has a diameter of 150mm, the grow room will require an intake of 2 or 3 x 150mm or rectangular ventilation grilles with an equivalent surface area. When installing passive intake, the extraction fan should always be placed at the opposite end of the grow room.

1-Flexible Ducts (Ventilation Ducts)
2-Intake Fan
4-Carbon Filter
3-Extraction Fan
C- Damper air
F- Filter Box

Second method: Set up active inline fans that push fresh air into the grow room. This installation is more efficient than passive ventilation.

1-Flexible Ducts (Ventilation Ducts)
2-Intake Fan
3-Carbon Filter
4-Extraction Fan
C-Damper air
F- Filter Box
G- TM Junction
H- Damper air

During the cold winter months, it is strongly advised not to draw air directly from the outside but rather to take air from a cool room inside the house (such as a bedroom or living room).

1-Flexible Ducts (Ventilation Ducts)
2-Intake Fan
3-Carbon Filter
4-Extraction Fan
C-Damper air
F-Filter Box
G-Junction
H-Damper air

During the summer months, it's preferable to draw in outside air through a cooler (or air from an air conditioner) rather than air from the house, which can be too warm.

Source of fresh air in the summer: Whenever you intake air directly from the outside, it's advisable to use a filter box (with a flat filter element) or (with a V-shaped filter element, which enhances filtration) to prevent the intrusion of pests and other insects.

To prevent the return of used air, install backdraft dampers that open when the ventilation system turns on and close when it turns off.

1-Flexible Ducts (Ventilation Ducts)
2-Extraction Fan
3- Carbon Filter
C- Damper air
A-Fan

It's advisable to split the air using a T or Y-branch to ensure that the cooled air is distributed evenly.
Position your intake air near the source of fresh air and push it into the grow room to filter the air more effectively. Place your extraction fan near the source of heat for efficient ventilation.

Note: When installing an exhaust fan, it's crucial to ensure that it provides the required air for the surface area.

If you introduce more air than the extraction fan can remove, air starts to accumulate and causes "positive pressure," pushing untreated air out of the grow room. Therefore, select an intake fan with a maximum air capacity and flow rate that is 10-20% lower than the actual output of the extraction fan to create "negative pressure."

To find the diameter of the intake fan, you'll need to take the power of the extraction fan and apply an estimated reduction for the carbon filter - 25%. If our goal for the intake fan is a flow rate 15% lower than the extraction fan, we need to multiply the reduced output by 0.85. Below is a model to size the intake fan for an example with 2 600W lamps.

Below is a diagram showing how to "calculate" the required intake for a room equipped with 2 600W lamps:

[Estimated extractor capacity with a carbon filter] = [Air extraction capacity] x 0.75 = 585 m³/h [Intake air capacity of the fan (with a reduction to ensure negative pressure)] = [Estimated air extraction capacity with a carbon filter] x 0.85 = 497 m³/h

For this intake flow rate, the closest and widely available product is a 150mm fan.

Note: When installing the intake fan, make sure that the extraction fan is installed at the opposite end of the grow room.