After you've decided your mounting type, you'll want to narrow your search down to the correct width for your new vent hood. In order for your ventilation to be most effective, you'll want your hood to extend three extra inches on either side of your cooking equipment so that it can catch any smoke that may roll out the sides. For example, if you have a 36-inch grill, you'll want to get a 42-inch vent hood. When it comes to vent hoods, you'd rather go bigger than smaller. If you don't find the exact size you need, it's best to go one size higher.