question on range hood sizing please

springplanterMay 7, 2013

I think I am confused. We will be installing a 36" AG Wolf (one of the last of its kind) with a freestanding hood (no cabs) above it. It will be a custom hood. Going by the suggestions that there be 3" on each side, we have been examining the 42" hood inserts. My doubt is that I now wonder if what I need is a 36" insert because with the liner it will end up to be the 42"

Any help from the experts here would be appreciated


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It is the internal aperture that matters. Because the rising cooking effluent expands as it rises, the hood needs to overlap the areas of the bases of the pans doing the cooking. This leads to the 3-inch rule of thumb, but that is only approximate, as the fact of the expansion angle means that the higher the hood the larger the aperture has to be for full capture.

While the expansion angle varies with what is cooked on what surface at what temperature, a nominal value of 22.5 degrees half angle can be used measured from the edge of the heated part of the pan (not necessarily the edge of the cooktop). This value may be found in some reports referenced in my Clippings for commercial cooking devices. I observe lower dispersion angles using a wok on a Cooktek wok hob. The 22.5 degree angle will usually lead to a larger aperture than anyone will tolerate in a residential setting, hence the 3-inch rule.

To the best of my knowledge, inserts and liners are terms that mean the same thing. One purchases what is essentially a hood that does not have a finished outside surface - a liner. This liner is covered by (typically) cabinetry, making the visual hood larger. But it is still the internal aperture that has to collect the effluent. Hoods do a very poor job (at any air flow rate anyone could stand in a home) at pulling in effluent from the sides, hence the need to overlap the pan areas. Capture from outside the aperture will be only a few inches at most, and that requires high specific flow rates -- perhaps at least 90 cfm per square foot of aperture.


    Bookmark   May 7, 2013 at 12:08PM
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