It is advisable to keep vent hoods vented outside. A vent hood is regulated by CFM, which is directly proportional to the size of your kitchen. CFM is normally used to determine the volume of air the hood can exhaust per minute. This in turn predicts the efficiency of the hood in terms of exhausting smoke, odors, grease and other gases out of your kitchen. Higher the CFM, greater is the volume of air pulled out through the hood.
It is a common notion that CFM is related to the amount of heat produced by the stove, that is, the number of BTUs that it is rated for. Another major factor is the type of cooking that you normally do. If your cooking mostly comprises of stir fries, searing at high temperatures or grilled food, then your CFM requirements are much higher than someone who cooks mostly light stuff. If you are fond of Asian stir fries, you need higher CFM, while if you are mostly into making oatmeal, you would need lower CFM.
It is necessary to discuss the concept of “capture area” in the context of CFM. Simply speaking, it determines how big the hood is. If the hood is too small, the grease and smoke will drift out and get away from the range of the hood. Even a high CFM will not be able to pull smoke into the hood once it has drifted out of the hood range. It is important that the hood should be at least 3” wider on both sides of your range than its own size. Also, the hood should not be placed high above the range surface. 30” is mostly considered ideal.
Revised codes for new buildings and residential homes demand that bathrooms and kitchens need to be ventilated to the outside, not into an attic. While purchasing a new vent hood, observe the exterior of the box carefully. It will mention how much CFM it uses. Eight inch is the size of a standard pipe. However, some require larger sizes. This pipe needs to have a damper. It will maintain a cool air inside your home during summer times when the vent hood is not in use. This will help you save a lot of money on your electricity bill.