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Is a 900 cfm hood enough for this situation?

Posted by kaysd (My Page) on
Thu, Aug 16, 12 at 15:20

I bought a 36" Wolf AG range with four 16,000 btu burners and a 16,000 btu charbroiler. I don't know if we will use the charbroiler, as we grill outdoors year round (bought a floor model or would have skipped that feature). We have a 10' ceiling over the range, but there is no second floor or attic above the ceiling. The distance from the bottom of the hood to the top of the roof is a straight run of less than 5'. If I have read other posts correctly, it appears long runs and bends reduce efficiency, so higher cfms are needed? I know 1000+ cfm is usually recommended for a range with grill, but I wonder if I need it with such a short, straight run.

My other option is to purchase a higher cfm exterior blower, but both the unit and installation will cost more, and our GC just discovered major plumbing issues in our slab so I need to watch costs very carefully. I don't think a roof mounted blower will be much quieter in our case than an internal blower given the 5' distance, but please let me know if that is an incorrect assumption.


Follow-Up Postings:

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RE: Is a 900 cfm hood enough for this situation?

An external blower with a short run would probably not be quieter than an internal blower, but that could depend on the design. A large slow fan would have lower blade tip turbulence noise, but the baffle noise and duct noise would remain. An in-line silencer (monster "muffler") would quiet much of the external blower noise, but they are large and might be considered un-aesthetic mounted over the hood in the kitchen.

Cooking cfm required depends mainly on the hood aperture, which should be big enough to capture the rising and expanding cooking effluent plume. Larger hood, more cfm; smaller hood, escaping moisture, grease and odor. Be sure that there is enough make-up air, or the actual cfm will be much lower than expected. In any case, the cfm will be lower than rated because there are still pressure losses in the path between aperture and exit. With open windows one might get 700 (wild-guess without a fan curve) with a short length of 10-inch duct and baffle filters.

kas


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RE: Is a 900 cfm hood enough for this situation?

Thanks, Kas. The hood would be 42"x24" over a 36" range. MUA should not be a problem because we open the kitchen window when we are home pretty much year round. (Plus, our 52 year old house is not exactly air tight. No fireplaces either.)


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