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.
| Suction Quality | Velocity | Best Case Use |
| Weak | < 8 m/s (1,500 FPM) | Ineffective for grease/smoke |
| Moderate | 8–10 m/s (1,500–2,000 FPM) | Decent for standard cooking |
| Strong | 10–15 m/s (2,000–3,000 FPM) | Good for most residential cooking |
| Very Strong | >15 m/s (3,000+ FPM) | Best for heavy/BBQ cooking |
🔍 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:
- Match fan size (CFM) to stove size and cooking habits
- Light cooking: ~300–400 CFM
- Heavy/frequent cooking or gas stove: 600+ CFM
- Use the right duct size
- Undersized ducts = backpressure, velocity drops, poor suction
- 6" minimum for most range hoods; 8"+ for 600+ CFM
- Minimize bends and long duct runs
- Each bend adds static pressure → lowers velocity and airflow
- 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
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