Well I don't know about the counter math as it relates to hood depth. I think it's more about fitting the hood to the cooktop. Some like a deeper hood for improved capture area, thats good. But you might end up bumping into it once or twice before you get used to it. A little give and take here, nothings perfect. Also depends on your cooking style and how much oomph you need from the hood. Generally speaking you would want to go as big as you can with the hood and be comfortable with the look.

Deeper is better - otherwise you'll end up cleaning grease off the front of the hood.

Buehl,
Based on the info you have provided you will be fine with either a 21" or 24" deep VAH. The National Kitchen and Bath Association recommends that a hood should extend over the cooking surface by 3" to both the left and the right as well extend forward far enough to cover the front burners. That being said, if your design does not allow for the overlap to the left and right I would default to a PRH9-136 at a minimum. The 27" hoods offered by VAH are really intended for pro style cooking equipment that is usually equipped with a grill or griddle or for the outdoor grill in a three season porch or outdoor kitchen. Hope this helps.

regards,

Indy

Well, being an owner of a hood that "extends over the cooking surface by 3" to both the left and the right as well extends forward far enough to cover the front burners" I politely disagree with the NKBA standards.

Just covering the front burners isn't enough, you want it to overhang them a bit. This is because the front part of the hood has the lights and switches on it, so that deflects some of the vapors. If you have an electric cooktop in a standard depth counter, the 24" should be fine. If you bump out your cooktop, go with the 27".

My apologies. I went back and read the original post and I realized I read the post incorrectly. I agree with alku05 in regards to going with the 27" hood if you bump the counter out. However, if you don't bump it out, the 24" hood will be more than adequate based on the fact that most electric cooktops have an average overall depth of approximately 21" (i.e. Wolf CT36E).

regards,

Indy

Thanks all! We are going with a 42" width hood so it extends 3" past on either side, but I wasn't sure about the depth. Our current one is an old builder grade under cabinet (GE) it's depth is 18" and is 24" above the range surface...I do bump my head on it occasionally--still do after 12 years.

As Alku05 says, it does seem to me that you would want it to overhang the burners to catch steam, etc. that doesn't always follow the "rules" and go straight up :-) We don't fry or use a wok, but I do brown meats, etc on the front burner and I don't want to be cleaning the front of the vent all the time.