The sq.ft. of the kitchen has little to due with the hoods CFM, however, the mfg. of the cooking appliance's recommend venting CFM does.

I'm sorry...I don't understand. If the cfms & sq footage don't matter, how would I determine which hood I would need? (I already know which style I want & the size I need but I have noticed diff brands/models have diff cfms)

sher. There are a number of factors that go into the decision of hood size. You need to know the output of the cooktop/range that you will be using. In other words heat from the unit...so gas or electric how much heat does it generate. Then you have to think about how you cook. Do you stir fry...ie. lots of grease and smells or do you reheat take out ...lots of variance in the spectrum of use. Baffles/mesh...remote blower, inline...there are a lot of things that you need to consider.

The bottom line is what and how you cook. The area of your kitchen has nothing to do with it. The size of the cooktop...30", 36"...etc and the type ....gas or electric. I think you need to Google and read a lot of facts before deciding. There are a number of threads that are recent on hood choices. Try a search and then come back and ask questions. Also the Appliance Forum is a very good source of info. You do need more info before you know what the right questions are :) c

The general rule of thumb is 10 CFM per 1K BTU of the cooktop. So if you have 4 15K burners (60K total) you would need 600 CFM. However, the "rule" somewhat over states the issue to sell you more than you need since you generally won't be running all the burners at maximum at once. In general, I believe that 600 CFM will be adequate for most ranges. Adding a grill to the cooktop which will produce a lot of smoke may increase your need for additional CFMs. The size of the capture area of the the hood is important too - you want to cover the front burners so a hood that is 27" deep is an excellent choice. Many recommend getting the hood 6" wider than the cooktop - this is ideal with an island hood - if your hood is wall mounted and you have cabinets on either side, you can generally get by with a hood as wide as your cooktop. If you go above 600 CFM you may need makeup air - there's a faq on the appliance forum about. Some on the appliance forum recommend going way high on the CFMs and that's not a bad idea if you have a grill and/or do a lot of smoky, greasy cooking.

Thanks for the info! I had done a search, but somehow missed that Vent overview on the Appliance forum. Just found it though!

If you want some great information, I'd search the Appliance Forum where hood discussions have been rampant recently. Cfm ratings may be somewhat related to room size, but that is not a major consideration.

Cfm's are generally used to estimate how much air the hood will exhaust per minute. That in turn predicts how well the hood will function to do what it's intended to do--which is to exhaust the combination of smoke, grease, odors, and combustion gasses out of your kitchen. Higher cfm means of course that more air is being pulled out through the hood and should correlate with how effective the hood is.

As a first approximation, cfm are generally correlated to the amount of heat the stove produces--the number of BTU's that the burners are rated for. Some quote a "100:1" rule--for every 100 BTU's your range produces you need one cfm. I think that underestimates the cfm required for top notch ventilation but there are other factors that may be more important.

Another major factor is the type of cooking you do. If you stir fry, sear at high temps, saute bacon all the time, or have a grill that you intend to use, then your cfm requirements are way higher than someone who rarely cooks with high heat and doesn't do much "smelly" cooking. So--spicy Asian stir fry--lots of cfm. Mostly making oatmeal--fewer cfm needed.

The other side of the coin is that cfm are not the only determinant of successful ventilation. Equally important is the concept of "capture area." That's a fancy way of saying how big the hood is. Too small a hood and the grease, odors, etc will end up drifting out and away from the range and out of the reach of the hood. No amount of cfm's will pull smoke into the hood once it has drifted out of the hood area. A very simple rule is that the hood should be at least 3'' wider on each side than your range. The other factor is that the hood should not be too far above the range surface. 30'' is often quoted as ideal.

So...what you really need to make this decision is:

1) the type and configuration of the range you're ventilating
2) the type of cooking you intend to do
3) the size of the hood you are thinking of installing

Then, you can begin to get into all kinds of specifics, like the size and length of ductwork you're using, the type of blower you want to power the hood, etc etc etc. For that, again, it's time to head over to the Appliance forum. Look for posts from folks like kaseki, weissman, breezy 2, (and me too, as I have bored people to tears over there with hood lore).