How to Calculate CFM of Exhaust Fans for Greenhouses

Greenhouse ventilation volume is based on a specific formula related to the greenhouse dimensions no matter what your plant types and climate zone are. Although it may seem complicated, choosing the right shutter exhaust fans for your greenhouse cooling system does not require complex mathematical formulas or difficult calculations，to find out how many CFM(cubic feet per minute) do you need for greenhouse and how many exhaust fans you need for your greenhouse, only one  simple greenhouse exhaust fan calculator tip is all that’s needed. We’ll show you how to do them below.

First, Calculate Total CFMs for Greenhouse Exhaust Fans

Greenhouse cooling fan capacity is rated in Cubic Feet per Minute (CFM) which measures how much air the exhaust fan pushes through in a measured time, Calculating CFM’s depend on the airspace in your greenhouse, so to choose your correct greenhouse exhaust fan size in CFM, normally we’d recommend 20,000CFM for every 100㎡or 1000 sq.ft greenhouse of 5 meter height, or 25,000CFM fan for every every 100㎡or 1000 sq.ft greenhouse higher than 7 meters.

Then the total CFM required for the greenhouse ventilation fans is:

Length(m) x Width(m) ÷ 100 x 20,000= ventilation volume(CFM).

If the dimensions of a greenhouse are 30 meter long, 9 meter wide, and 5 meter height, now you can use the calculated air volume to get the total CFM for your greenhouse

30×9÷100x 20,000=54,000CFM

Second, Exhaust Fan Calculation Sizing in your Greenhouses

Using your total CFM to decide what size exhaust fan you will need for your greenhouse, divide the total CFM by the required number of fans in the space. Then, pick the types of fans you need according to safety standards.

Greenhouse exhaust fans provide ideal passive cooling, especially installed with evaporative cooling pads on the opposite to create negative pressure cooling, while indoor/outdoor circulation fans are built to withstand humidity levels.

Here are some sizes of exhaust fans for your reference. You may use the chart below to determine what size fan you will need.