Components
Vent hoods are simply a fan and/or light housed in a metal and/or glass shroud.

Principle
The metal/glass shroud acts as a deterrent to the spread of a stovetop fire, and helps to collect cooking fumes. The fans come in two varieties, rotary or centrifugal and performs either of two actions:

1. For an external/outside vented system, it draws fumes and odors up or down--depending on the style of vent hood--through a grease filter inside a duct system and out of the house.
2. For systems without external/outside venting, fumes and odors are drawn over an activated-charcoal filter and re-circulates the air, back into the room.
   

Range Hood Vent Buying Tips

1. There are two types of fans in range hoods, the traditional bladed rotary fan, the most cost effective models and the barrel-shaped centrifugal. The centrifugal works best when installed in ducts and will move more air and is quieter to operate. Select a range hood with rotary fans for less expense.
2. For more flexibility and control look for range hood fans with variable speed controls.
3. The amount of air that the vent fan circulates will correspond to the effectiveness of removal of smoke and odors from your room. Air movement is measured in cubic feet per minute (CFM). Look for this rating on the units you are comparing. The higher the CFM the more air is moved.
4. Remember to consider the amount of noise the fan will make. If you are entertaining guests, while cooking you want to be able to hear them over the fan noise. Sones is a measure of perceived loudness and the units used to rate the noise produced by the fan noise. A refrigerator and normal conversation both create roughly one to four sones. Use sone ratings to compare units, but be aware that the higher the CFM, the higher the sone rating is likely to be.
5. Automatic shutoff can be preset to shut the fan off after a specific time, which is a nice feature if you finish cooking, want to sit down to eat, but leave the fan running a bit longer to clear the air.
6. Heat sensors are features that automatically speed up the fan or sound an alarm when they detect increased heat.
7. Lighting is also a nice feature to have as part of your range hood. Some come with one or two incandescent or halogen bulbs.
   

Installation considerations

• Proper size — for efficiency, the hood needs to be at least as wide as the range or cooktop. Units will mount either on the wall or under the cabinet — some are adaptable to mount either way. When selecting range hoods, measure your cooking surface before going shopping. Always read the specified requirements for the proper mounting height.
• Exhaust — since the idea is to remove air, the best range hood is only as good as its exhaust system. There are three configurations:
  1. Vented or Ducted —Requiring ductwork to channel the exhaust outdoors.
  2. Non-vented or Duct-free —With washable and replaceable filter(s) to clean and return the air to the kitchen.
  3. Combination — can be used with or without ducts.
     
• Location - Where will the range hood be located? If you select a ducted unit, the exhaust must be vented to the outside, never directed to the attic or basement. If your range hood will be mounted on an exterior wall, the exhaust ducts will be shorter and therefore more efficient. If you plan to install the hood on an interior wall or island, keep in mind the longer distance and consider a more powerful unit.
• Ductwork - Proper installation of ductwork is critical to the efficiency of the range hood. While many individuals choose to hire a professional to install their ductwork, you can purchase materials and accessories to do it yourself. Always read the manufacturer's specifications carefully.
• Design - Range hoods are available in many styles, from hideaway models to brushed metal units. The type of range you have, gas or electric will require different types of hoods. Look for models that are easy to clean, some have parts that can be put in your dishwasher to be cleaned.

Tricks to Keep Your Range Hood Vent Maintained

Filter cleaning/replacing
You need to periodically clean your over-the-stove vent hood. The thin, silvery screen is the grease filter (there may be more than one). It traps airborne oils and grease to keep them out of the blower and exhaust vent. To clean the filter, remove it and soak it in a degreasing solution until the grease is dissolved. Next, wash it with warm, soapy water to remove any traces of the degreaser. Then put it in the upper rack of the dishwasher and run it through a normal cycle.

Note… If your unit circulates the air rather than vents it, it may have one or more activated charcoal filters. Don't wash these. Just replace them when they lose their effectiveness. You can find replacement filters at RepairClinic.com.

Interior cleaning
Warning! Be sure the unit is turned off before you clean it. Also avoid spraying cleaner directly onto the light bulb or light bulb socket. Clean the interior of the vent hood with a standard household degreaser/cleaner.

Exterior cleaning
Clean the exterior of your vent hood with a degreaser/cleaner or a non-abrasive cleanser.

Fan motor care
Most vent hood fan motors don't need any maintenance. Over time, the motor and bearings may become stiff because of the constant heat, humidity, and grease to which they're subjected.

The blower wheel also gets greasy and dirty, over time, which can slow down the fan or cause vibration. Remove the wheel and clean it with a degreaser. Then, if the fan is still slow or if it vibrates, you need to replace the fan motor.

Vent cleaning
If your fan vents (rather than just circulates), you need to regularly check the vent that leads from the vent hood to the outside, to make sure that grease isn't building-up on the inside of it. If it is, contact a vent-cleaning contractor to clean the vent properly. (You may find such a contractor under "chimney sweeps," or "HVAC duct cleaning," or "ventilation cleaning" in your telephone book Yellow Pages.)