Choosing Vent Hood Depth

saskiasmomApril 5, 2008

As I have posted before, I'm planning on a BlueStar 6-burner range. If you were choosing a hood, would you decide on one 36 in. wide by 27 in. deep or one 42 in. wide by 24 in. deep? (The ceiling is 8 feet. and the wall is 58 in. wide.)

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I have a related question. If one chooses a 27" deep hood, which is deeper than the cabinets, do you have to install it higher than you would one that is only 24" deep? I think I'm short enough not to have an issue, but taller folks could get dents in their heads... How much higher can you raise it before you have to consider increased capacity?

    Bookmark   April 5, 2008 at 1:56PM
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I'd choose the 36" by 27" - in my experience depth is more important than width particularly if you have cabinets on either side of the hood.

Most hoods recommend 30" to 36" above the cooktop. Mounting it at 30" will make it more effective.

    Bookmark   April 5, 2008 at 2:16PM
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Honestly, 42" by 27" is best.

    Bookmark   April 5, 2008 at 3:21PM
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Absolutely 42 x 27. I have a 30" BS with a 24" deep hood, and every time I sear something or stir fry I regret it.

    Bookmark   April 5, 2008 at 3:37PM
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It may be worth sketching a side view of the range, hood, and stick figure cook on grid paper (to scale) to see what sightlines may be obscured and foreheads bumped with the hood at a given height. Writing as a slightly taller than average [sometimes D]H, I would be seriously annoyed if I couldn't see what I was doing or had to wear a hard hat to cook.

My choice is to move the hood heigher and buy a larger exhaust fan. How much larger? Now you are into very wordy territory.

In still air, growing the overhang is more important because the rising effluent plume expands at a relatively fixed angle, at least until it hits the back wall or side cabinets. In real conditions, air disturbances can displace some of the effluent and cause it to miss the hood. This calls for extra air flow to compensate, and I am not aware of any studies of this topic. Greenheck literature recommends a factor of 1.1 when raising typical commercial hoods from 6 feet, 6 inches to 7 feet. These hoods already have significant overhang, however, so a marginal residential configuration will likely need a larger factor.

In any case, at the burner 30 or more inches below a hood, there is very little airflow velocity from the hood flow itself. The uprising effluent velocity is the primary means of getting the effluent to the hood. Outside the hood edges, the airflow velocity from the hood is also relatively low, so it is difficult for the hood flow to make up for too small an overhang.

Take your pan size to be used on a front burner, put it on your sketch. Sketch a line upward toward the hood starting from the pan edge, angled at 1.5-inches per foot in the direction of the cook. Ensure that the hood captures this line.

A pan that extended to the 24-inch counter line, three feet below a 27-inch hood, would only have one inch per foot of angle growth. At three feet of hood spacing for a 27 inch hood, the pan edge must remain behind the counter edge by 1.5 inches to meet the rule. A 24-inch hood can be seen to be very restrictive in this regard, suggesting that frying be done on back burners only.

Some overcome hood extension limitations by spacing them out from the wall and putting a filler piece of stainless between the back of the hood and the wall.


    Bookmark   April 6, 2008 at 9:14AM
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Just be sure you cover the front burners!

    Bookmark   April 23, 2008 at 5:38PM
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Thanks Kas, that was helpful. Keitel, how far above the cooktop is your hood? Do you ever bump into it now? What if it was 3" deeper?

    Bookmark   April 24, 2008 at 1:42AM
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The height of the hood should be 30-32" above the cooking surface. Moving the hood higher, will make it less efficient. If you must move you hood to 36" or above, be sure to incresase the width and the depth of the hood. As smoke and steam rise, they tend to disipate. Increasing the cfm above the manufacturers recommendations does not do a lot of good. Most manufacturers will have you sign a disclaimer if the hood is going to be above 36" or underpowered.

    Bookmark   April 26, 2008 at 1:33PM
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My hood is 30" over the range and it's a bit awkward to get to the back burners. It would be impossible for me (6'1") to work with a 27" hood at a 30" height. If I were to have a 27" deep hood I'd definitely need to raise it to whatever I could while still allowing it to work i.e. 32-36".

    Bookmark   April 26, 2008 at 3:31PM
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I went with 58x27 over my 55" stove. It's mounted 35" above the stove so that access to the back burners isn't an issue for anyone over our height (we're 5' and 5'7" so really it wasn't an issue for us). But I did want someone like keitel to be able to cook at our stove without putting an eye out :)

We did raise cfm's as well, and did this with the manufacturer's advice all the way through (vent a hood). We had to do some fancy building to make it work easily (we basically rebuilt the shell of the insert and put the works back into it as looks like it did when we got it...48x22...but is now 58x27 ). Rebuilding the body gave us a bigger capture area than just adding stainless trim to the base surface. This was what vent a hood advised as a best case scenario.

    Bookmark   April 26, 2008 at 4:04PM
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Here's what we were told, by an "expert."

For our planned 48" BS, we could get a 48" by 24" vent hood to set at 30" above the stove, with a 600CFM exhaust fan. Or, we could get a 48" by 27" hood to set at 36" above the stove, with a 1200CFM exhaust fan. (To set a 27" hood lower than 36"" above the range top would cause the bumping of many heads.)

Either way, the evacuation rate across the stove top would be "about the same." And the larger fan would make more noise, even though we plan to install it at the roof.

Soooooo..... We ordered the 24" hood to be installed at 30" above stovetop with the 600CFM fan. Check in about two
months and I'll give you a researched opinion (is that an oxymoron?).


    Bookmark   April 28, 2008 at 3:18PM
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jimjanhenry, do you have a researched opinion for us yet?

    Bookmark   October 15, 2008 at 9:35PM
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Depends as the hood gets higher it becomes shallower. If I hang the hood 28 to 30 inches off the cooking surface and it has all burners no grill and I am not a heavy fryer or WOKer than a 22" deep hood with 600 or more cfm is fine. If I hang the hood 31 to 34" off the surface I would suggest a 24" deep hood with the same power above 34" go to the 27" deep hood. If I am adding a grill or heavy frying or WOKing than I would add width to the hood as well as depth and consider a in-line or remote blower.

    Bookmark   October 16, 2008 at 8:34AM
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This is a 72" height of a 42x27 hood over a 36" range. The range sticks out beyond the cabinets as well as the hood.


    Bookmark   October 16, 2008 at 10:56AM
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Our example that worked out in the long run...

We purchased our appliances that included a Vent-a-hood (2-speed 300 CFM and 600 CFM) 42' x 24" for our 36" wide gas rangetop. Hood is mounted 30" above rangetop. We thought we'd have 1" front overhang since the hood has 3 cm slab of granite for backsplash. Long story short, we pulled the rangetop counter forward 3" during the design phase for greater visual appeal. We never changed hood depths...

With a large fry pan (12"), the outer edge of the pan extends several inches beyond the edge of the hood. But, even on low speed (300 CFM, but 450 equivalent CFM), smoke rises up and is captured by the hood.


    Bookmark   November 2, 2008 at 6:50PM
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ok...just so I understand, if I'm buying a 27" deep hood, optimum installation height should be about 36" above the counter so there is no head banging?

    Bookmark   February 28, 2009 at 4:30PM
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