Best Range Hood Size

There are three key components in selecting the proper ventilation system for your installation. 

1. Duct path. Improper ducting can diminish the ventilation system efficiency. The professional installer will follow the recommended proper duct layout,  and the guidelines set forth by ventilation manufacturers. The number of allowable elbow turns and the length of the run will directly influence the size of the fan required to compensate for the longer distance and increased resistance. . This layout should be prepared before specifying the system. 
2. Hood width and depth. Range Vent Hoods should be the width of the range it is venting or wider. Extending the hood width 3″ – 6″,  beyond the width of the range width, will provide the best possible capture of grease, smoke, and steam. Effective ventilation is always critical but even more critical with a gas cooking system. When cooking on a gas cooking system, there are byproducts of combustion, one being carbon monoxide. Because gas combustion produces water vapor, moisture is also an issue.
3. System Power. The system should be strong enough to remove moisture and pollutants but not too large/strong that it creates an alternate serious set of problems. CFM -Cubic feet of air removed per minute.  Exhaust hood systems that exhaust CFM at a rate in excess of 400 CFM must have, mechanically or naturally,  a make-up air system at a rate approximately equal to the rate of air exhausted. (See HVI Chart above) 
4. Operational noise level. The level of noise produced by the ventilation system when in use is measured in Sones. The lower the sones number – units of loudness –  the quieter the system. (See above reference chart.) The level of sound produced by the ventilation system may not seem important.  However; it quickly becomes important if your’s is loud and you can’t hear the person across from you. 

The vertical clearance above a range/cooktop surface to the bottom of any approved vent hood or other approved noncombustible material should be no less than 24″.  The vertical clearance above a range/cooktop surface to the bottom of any combustible materials or metal cabinets should be no less than 30″.  

The exhaust duct must be vented to the outside, not into the attic, soffit, ridge vent,  or crawl spaces. In the  “old days” (prior to the knowledge that it is unhealthy, will promote mold and mildew, and release back into your environment the pollutants you are trying to remove) the exhaust vents for the bathroom and kitchen were vented into the attic/eve-vent and left there to wreak havoc. DO NOT DO THIS. If this is how your exhaust vents are installed, have a professional vent them through the roof to the exterior …immediately.

Ventless hoods don’t remove pollutants to the same degree as a vented system. The ventless unit simply recirculates the air through a filter to remove a portion of pollutants, dispersing the remaining back into the air.