Choosing the Right Size of Inline Fan for Indoor Grow Tents

Multiple questions arise for beginners new to indoor weed cultivation. Among them, one tricky question is - what size of inline fan should I have for my grow tent? A properly sized inline fan ensures optimal airflow, keeps temperatures in check, and promotes healthy plant growth. If you're unsure where to start, this guide will walk you through the process of determining your grow tent's fan requirements and selecting the best inline fan for your setup.

Step 1: Calculate Your Grow Tent's Base Airflow

Every grow tent requires a certain amount of airflow to maintain optimal conditions. To figure that out, airflow is measured in cubic feet per minute (CFM), representing the volume of air your fan can move in one minute. Here’s how you find the base airflow requirement:

Volume (CFM) = Width x Length x Height

For example, a 4x4 grow tent measuring 4 feet wide, 4 feet long, and 6.5 feet tall has a volume of:

Volume = 4 ft x 4 ft x 6.5 ft = 104 ft³

This means the base fan requirement is 104 CFM to exchange the air in the tent every minute. Depending on your setup, you may not need to exchange air that frequently and can adjust to a replacement every two or three minutes if heat is less of a concern.

We have now calculated the basic airflow, but is that all? Nah, there is more.

Step 2: Adjust for Additional Factors

In addition to the base airflow, your grow tent setup often includes additional components that reduce a fan's efficiency. To compensate for these, you should increase your airflow calculation as follows:

• Grow Lights: Add 10% for each light.
• Carbon Filters: Add 25% for each filter.
• Ducting: Add 1% for each foot of ducting.
• Duct Bends: Add 30% for each 90-degree bend or 15% for each 45-degree bend.
• External Heat: If your grow tent is in a warmer location (e.g., attic), add 10%.

In this case, for a 4 ft x 4 ft x 6.5 ft tent:

• One grow light: +10%
• One filter: +25%
• Five feet of ducting: +5%
• One 90-degree bend: +30%

Total percentage increase:

10% + 25% + 5% + 30% = 70%

Convert this to a multiplier:

1 + (70/100) = 1.7

Multiply the base airflow (104 CFM) by this multiplier:

104 CFM x 1.7 = 176.8 CFM

Additionally, running a fan at its maximum capacity can increase noise and wear. To ensure efficiency and longevity, add 25% to the total CFM:

176.8 CFM x 1.25 = 221 CFM

For this example, a 6-inch inline fan rated at 402 CFM would be appropriate, providing room for future expansion. 

Inline Fan Recommendation for Grow Tents of All Sizes 

We understand - you do not have time to go through the calculation process above. That’s why we prepared the table for you, a complete inline fan recommendation for grow tents of all sorts. Instead of measuring on your own, check the table below to know the exact fan requirement for your grow tent.

Pre-condition:

• For grow tents smaller than 5x5, we have set up 1 grow light and 1 carbon filter.
• For 4x8 grow tents and 5x10 grow tents, 2 grow lights and 1 carbon filter are prepared.
• For 8x8 grow tents, there are 4 grow lights and 2 carbon filters.
• 25% extra capacity has been added to make sure the values above are the ideal fan capacity.

To make a quick sum-up here, for airflow below 205 CFM, we recommend Mars Hydro 4" inline fans. For airflow below 402 CFM, we recommend Mars Hydro 6" inline fans. For those above 402 CFM, we recommend using multiple inline fans in your grow tent. 

In addition to offering inline duct fans of different sizes, Mars Hydro never stops enriching its product with precise, delicate, and useful features. What does that mean? At Mars Hydro, you can find inline duct fans with speed control, Bluetooth control, & thermostat controller, with each catering to different targets. 

Check our guide for more on these amazing inline fan series: The Importance of Inline Duct Fans for Indoor Gardening