36 vs 42 prestige hood

4 years ago

KD suggested 42 may be too big (aesthetically)for this space. i’ve already ordered the range (26” gas w a griddle!) so no backing out. wondering if he’s right about the aesthetics considering the size and layout of my kitchen. thank you!

Featured Answer

kaseki

4 years ago

The issue with overlap vs. no overlap is that some plumes (from hot oil or grease at the smoke point, for example) are high velocity -- up to 3.2 m/s, and since they are expanding as they rise the no-overlap scheme has to pull the plumes into the hood from outside the hood boundary. This is difficult because the air flow rate from a hood rapidly drops with distance in the zone transverse to the hood edge. (See Fig. 6, page 30.4, 2003 ASHRAE HANDBOOK, HVAC Applications.) One could be down to 20% flow rate at only a few inches from the entry aperture.

Side skirts on commercial hoods, and side cabinets acting as partial sideskirts can help with this, but if the pan edge is close to the point below the hood entry aperture edge some effluent is very likely to escape.

If the most odoriferous or greasy cooking is done near the center of the rangetop, or on smallish pans near the edge on rear burners that might have some cabinet blocking, one might avoid the worst effects from inadequate capture. Obviously, more CFM will help, but the reference figure suggests that it will be a losing battle with strong plumes.

Depending on one's intended cooking style, it might be necessary with an undersized (non overlapping) hood to aim for an actual flow rate into the entry aperture well above the recommended 90 ft/min.

Performance, Aesthetics, Affordability: Pick at most two or trade off among them and accept the resulting penalties.

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Comments (6)

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Sabrina Alfin Interiors
4 years ago
I agree 42" is too big. You've got a small kitchen and you don't want the hood to completely take over the space. Get a 36" to align with your range; just make sure it's powerful enough to do the job.
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Georganne Dermigny
Original Author
4 years ago
@kaseki thanks i've read many of your posts but they go over my head! i think i will have to go with the 36 hood. not sure how to "aim for the actual flow rate..."? the plan was to place it 28 inches above the range but KD said code is 30 which makes no sense to me. i would think if its lower, its bound to capture more...?

i dont cook greasy foods. i'll use the griddle a lot for searing fish and very rarely a steak for guests (is that how one even cooks a steak? ha) and the burners will be for soups and some veggies. i stir fry sometimes as well but most of the time i'm cooking for one. the prestige blower is 1200cfm. thanks again!
kaseki
4 years ago
The deeper the hood (front-to-back) the better the capture. The deeper the hood the harder it is to see into pans on back burners unless the hood is higher than one's eyes. Also, the hood and/or any wood or other combustibles that are put around it has to be a certain distance above the cooktop, determined by the hood installation guide and the range installation guide. I wouldn't go under 30 inches myself. My Wolf Pro Island hood is at 34.5 inches above my cooktop -- just over my head. No wood is involved.

I don't know how deep this Prestige hood is. If it were 24 inches, say, and 36 wide, then that is 2 x 3 ft for an aperture of roughly 6 sq. ft. At 90 CFM/sq. ft. = 90 ft/min, you would need a flow rate of 540 CFM. A factor of 1.5 on blower rated flow rate to 810 CFM would be advisable because blowers do NOT actually flow their rated CFM when installed in a hood/duct/MUA system. However, the factor of 1.5 assumes actual low pressure loss MUA, and no extra flow rate for improving capture of the just-missing-the-edge effluent. So your 1200 CFM rated blower, maybe flowing 800 CFM actual, or less with only window screens for MUA, or whatever your unstated MUA plan is, will help. Some air may be pulled through wall cracks, though, without adequate MUA, and the actual hood flow rate will suffer.

Note that in many municipalities, deliberate MUA is required for blowers of this rating. Even without this code requirement, if any combustion appliances are present without their own MUA separate from the kitchen air, there can be a carbon monoxide back-draft hazard.
Georganne Dermigny
Original Author
4 years ago
ahh ok that helps. interesting that no one ive discussed this with (KD, Prestige sales and tech) have mentioned MUA. so i will have to look into that. thanks @kaseki
kaseki
4 years ago
last modified: 4 years ago
Heh. While some are uninformed, and some are afraid that dealing with MUA details is outside their skill set, there is in general a reluctance to destroy sales by bringing up an issue that, depending on hood performance, may entail significant added cost.

It certainly entails planning as the architecture of the residence affects what one can do. The MUA 'system' plan should proceed in coordination with the hood system plan.

A search here on 'kaseki' and 'MUA' should lead to more MUA reference material. A search on 'opaone' and 'MUA' should extend this into interior air quality (IAQ) issues.

Keep in mind that perfect is the enemy of good enough, and that striving for the 100% solution may cost so much that no solution is adopted when the 80% solution may have been adequate and affordable.

Safety, however, is paramount. I strongly recommend that all combustion appliances have their own MUA so that the requirements for kitchen hood MUA can be relaxed. (This will depend on Code Enforcement, which should be consulted in such cases.)