Types of Range Hoods
Under Cabinet: This is mounted under the bottom of a wall cabinet with ductwork inside an adjoining wall, chase, soffit, or ceiling to exhaust smoke and fumes to the outside. This design is ideal for a remodel and/or replacing an Over-the-Range Microwave hood with something nicer.
Wall Hood: This hood is used when there are no cabinets over the range and mounted with exposed vent stacks on the wall to vent to the outside.
Ceiling/Island Hood: A four-sided hood that is anchored and vented through ductwork in the ceiling. The hood should be wider than the cooking surface to help funnel the fumes.
Over-the-Range Microwave: A Microwave with a fan built inside. These are not designed for heavy cooking, they max out at 3000 CFM and have a shallow capture area.
Downdraft Hood: These can be integrated into an appliance or rise up: separately they reverse the direction of rising smoke and fumes and generally exhaust them through ducts running beneath the floor. Downdraft hoods are best utilized in islands and hoodless applications. The performance of down-duct hoods are said to be sub-par in comparison with traditional vent hoods located above the cooking surface. As you’re cooking, vapors rise up , which is harder for a downward draft to capture. However, if aesthetics are highly important and you aren’t big on cooking, this is an ideal option.
Ventilator Power Pack: The blower without the decorative hood. These are intended mainly for use in custom or wood hoods.
Suggest CFM Requirements
The amount of air that is vented by fans is measured in cubic feet per minute, or CFM.
• Electric Ranges: Generally speaking these are low powered and should only need a range hood output between 150CFM – 300CFM.
• Gas Ranges: Regular gas cook tops have outputs of up to around 40,000BTU [British Thermal Units]. You can use a simple formula to help make your CFM choice. Calculate your cooktop’s BTU rating by adding the power of each burner and then divide the total by 100.
BTUs/100 = CFM
[i.e.: a 30,000BTU top will require a 300CFM fan] Keep in mind that CFM isn’t everything. More airflow does mean faster venting but does not guarantee better smoke capture and removal. Additionally, the more air you suck out, the more air you need to replace, this is called make-up air. New energy efficient homes are built with “air tightness” that can cause problems for range hoods with high CFM rates.
Ducted vs. Non-Ducted
A Recirculating hood is a non-ducted hood that directs steam, heat and smoke into a filter and then the air is recirculated back into the room. Its main filter can trap oil and grease droplets dispersed as well.
A Ducted hood has an outside exhaust. It takes smoke, odor, humidity and heat out of the kitchen by exhausting it outside the house. These are considered to be a better option because the excess heat and grease is completely removed from the kitchen.
VS. 
Blower Types
Most hoods, microwaves and downdrafts already have blowers. However, on many professional and high CFM hoods the blowers are separate. These can be located outside your house, inside the duct or inside the house.
Exterior Blowers –
These are quieter because they are located on the outside of your home. However they are big, bulky and hard to service.
Internal Blower –
This blower is mounted on the side of the hood. These tend to be louder, but are simple to service. They use an exterior wall cap, so they look nicer.
In-Line Blower –
Combination of external and internal blower. It is removed from the room, offering reduced noise yet located inside the duct work of the house.
Air-Ring Fan –
Shaped like a traditional fan, it discharges horizontally and is noisier. They are more economically priced, but less efficient.
Centrifugal Blowers –
This blower combines sufficient air pressure and constant speed. It doesn’t pull air through a filter but pushes the air around in a circular rotation pushing all grease and cooking particles out into an easy to reach housing unit.
Size
This is one time when bigger is better, don’t down size. Any hood you consider should have sufficient CFM and adequate coverage over your range top to trap the fumes. It’s always a good idea for you to check your local codes before hanging your hood as well.
• Height from Range Top: You should give yourself 30”-36” between your cooking surface and your hood. Keep in mind that the higher your range hood is from the range top, the less effective it will be. You can compensate for extra height by increasing CFM or coverage.
• Width (side-by-side): If your hood is located on an island, make sure it provides an overhang of at least 3“ on either side of the cooking surface. This extra width will help carry off more fumes and make your kitchen ventilation better. If your hood is mounted on a wall you can do exact match measurements. Make sure your hood extends out as far as your cooking surface for maximum efficiency.
• Depth (front-to-back): Under-cabinet and wall mount kitchen exhaust hoods come in depths of approximately 20”, 22”, 24” and 27”.