How Velocity Affects Range Hood Performance and Suction

Size and Velocity 

Velocity and size significantly influence the level of suction achieved. A smaller area will create a perception of greater suction. For instance, a range hood with a capacity of 1000 CFM in a 30-inch size will feel more powerful than the same 1000 CFM in a 60-inch size hood. This phenomenon occurs because an excessively large area combined with a low CFM results in a reduction in velocity.

🔍 What Is Suction in a Range Hood?

"Suction" typically refers to the hood's ability to capture and remove smoke, grease, and odors from cooking. It’s influenced by:

• Air velocity (speed of air movement)
• Airflow (CFM) — cubic feet per minute
• Hood design (e.g., canopy shape, filters, coverage area)
• Duct resistance (static pressure from bends, length, and size)

💨 How Velocity Affects Suction

✅ Higher velocity = faster air movement, which helps to:

• Pull rising smoke, steam, and grease particles quickly into the hood.
• Overcome cross drafts (like open windows or fans).
• Improve the capture zone — the effective area where the hood draws air.

BUT…

⚠️ Too much velocity can be bad:

• It can create turbulence, causing smoke to spill out instead of being captured.
• It can lead to higher noise levels.
• If not matched with enough volume (CFM), high velocity in a small area won't capture all the smoke.

📊 The Ideal Balance

Formula:

Velocity (ft/min) = CFM ÷ Duct Cross-Sectional Area (ft²)

• Ideal capture velocity at the hood face: 100–250 ft/min
• At the duct inlet (inside the duct): 1,000–2,000 ft/min is typical

Too low → smoke escapes
Too high → noisy, inefficient capture

🧠 Think of it like this

• Velocity = how fast the air is pulled
• CFM = how much air is pulled
• You want enough velocity to grab the contaminants before they escape, but also enough CFM to move the entire volume of air effectively.

✅ Tips for Good Suction Performance:

1. Match fan size (CFM) to stove size and cooking habits
   • Light cooking: ~300–400 CFM
   • Heavy/frequent cooking or gas stove: 600+ CFM
2. Use the right duct size
   • Undersized ducts = backpressure, velocity drops, poor suction
   • 6" minimum for most range hoods; 8"+ for 600+ CFM
3. Minimize bends and long duct runs
   • Each bend adds static pressure → lowers velocity and airflow
4. Use a well-designed hood with full coverage
   • Deep hoods with good canopy design keep smoke under control better than shallow ones

🔚 Bottom Line:

• ✅ Velocity helps suction by pulling air and smoke faster
• ⚠️ But only when balanced with CFM, proper ducting, and good hood design
• 🚫 Too much or too little velocity can hurt performance