Ventilation & Carbon Filter Sizing Calculator

Ventilation & Carbon Filter Sizing

Use Simple for a quick fan size based on room exchanges. Switch to Advanced to include filters, bends, duct length, and other losses.

Shop Fan + Filter Kits Ventilation Setup Guide

Ventilation & Carbon Filter Sizing

Use Simple for a quick fan size based on room exchanges. Switch to Advanced to include filters, bends, duct length, and other losses.

Tip: Many growers aim for a full air exchange every 1–3 minutes (tents) or use ACH 20–60 (rooms). Add losses for filters, long duct runs, bends, and silencers.
We’ll add typical filter loss (+25%) in Simple mode.
Typical: 20–30%
If using an inline muffler/silencer
Bug screens or filters restrict flow
CFM = cubic feet per minute
How to use this calculator (step-by-step)
  1. Enter room/tent size (L×W×H) or choose a preset.
  2. In Simple, pick an exchange time (minutes) and whether you have a carbon filter.
  3. Switch to Advanced to set ACH and add duct length, 90° bends, and accessory losses (filter/silencer/screen).
  4. Click Calculate to see Base CFM, total loss %, and Adjusted Required CFM.
  5. Use the Recommended Fan Target (adds 20% headroom) to select a fan and matching carbon filter.
Formulas: Volume = L×W×H. Simple Base CFM = Volume ÷ minutes. Advanced Base CFM = Volume×ACH ÷ 60. Adjusted CFM = Base × (1 + sum of losses). Headroom target = Adjusted × 1.20.
Ventilation & Carbon Filter FAQs
How often should I exchange air in my grow room?

For tents, every 1–3 minutes is common. Larger rooms may run 3–5 minutes or use ACH 20–60. CO₂-enriched sealed rooms can use lower ACH.

How much CFM does a carbon filter reduce?

Carbon filters typically reduce airflow by 20–30%. The calculator lets you add this in Simple or Advanced mode.

Do duct length and bends matter?

Yes. Long duct runs add friction, and each 90° bend adds ~10% flow loss. Keep ducts short and smooth for efficiency.

What size fan should I choose?

Use the Recommended Fan Target with 20% headroom. Pick the next fan class above that CFM rating.

How do I match a carbon filter to my fan?

Match the diameter (4", 6", 8", etc.) and ensure the filter’s CFM rating is ≥ the fan target.

Does CO₂ enrichment change ventilation needs?

Yes. Sealed CO₂-enriched rooms often use lower ACH to retain CO₂, but may need extra cooling airflow to control canopy temperature.