installing downdraft in half wall?

deedlesFebruary 25, 2013

Hello folks,

Hanging mostly over in kitchens but now have an appliance question. I want a downdraft fan and I want to build it into a half wall behind the stove. The wall can be built to accomodate the depth and I'd prefer an external blower if that matters.

Has anyone done this or seen it done or have a pic of it done. Looking at different models online, I see one mentions that it can be installed in a regular wall so I guess it can be done at least with that one.

Any help or advice would be greatly appreciated.

I'm pretty fixed on this option so as to be able to avoid overhead obtacles to the view of our little river out the porch windows. We have a vintage Chambers stove as you can see and don't do a lot of smoke producing cooking so I think this would be a good compromise for us.

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I find that my downdraft installed adjacent to the back of my cooktop (in the standard position) only really vents the rear burners. Your downdraft will be so far behind your burners that I'm not sure you would get even that much out of it. A simple exhaust fan in the ceiling and more frequent painting might be more exhaust effective and cost effective.

A few years ago, Gaggenau had a vent (meant to be used with their built in fryer I believe) that I considered. It was set in to the counter to the side of cooktop and swiveled over the burner. It seemed like it would be more effective than a downdraft but only good for one burner. I'm not sure I'm describing it well but you might want to take a look. I saw it at a Gaggenau/Thermador demonstration kitchen in my area.

    Bookmark   February 25, 2013 at 9:18PM
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Thanks judeny. I appreciate you sharing your experience.

    Bookmark   February 26, 2013 at 12:44AM
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The issue with downdraft venting is that the effluent rises from the pans at about 3 feet per second. In order to "bend" the airflow toward the pop-up downdraft aperture, vector analysis will show that the air velocity at the intake has to be much higher than that for reasonable height apertures. First, such a vent velocity would be very loud. Second, because the effluent expands as it rises, and the velocity of air past an aperture drops rapidly, extra factors of velocity would be needed to achieve capture.

A ceiling register of considerable size would be much more effective. At eight feet, the register would have to overlap the cooktop (pan edges) on all four sides by two feet. For example, with a 2 by 3 ft cooktop, the register area would be 6 ft x 7 ft. You may have a beam there that would make that difficult.

Air flow rate (cfm) should be sufficient to pull at least the area of the register (sq. feet) times 1.5 ft/s times 60 s/min. Because registers do not have the aerodynamic advantages of baffles, somewhat more may be needed. This will require a large fan, probably a commercial up-blast type will do. For the example above, 3780 cfm actual, requiring a 5000 cfm at zero static pressure fan. A commensurate MUA system would be required. Like a restaurant, your largest cost would be electricity if you cooked all day.

There is a reason why residential hoods tend to be over and close to the cooktop, and this reason is cost-effectiveness.


    Bookmark   February 26, 2013 at 11:26AM
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If you're willing to change your lights, you could put an 'insert' into the ceiling with a 'box' around it that would come down no lower than the beam in your picture. That would not interfere with the sight lines, though it might interfere with the cabinet on the right.

    Bookmark   February 26, 2013 at 12:34PM
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Kaseki: that's very impressive... you being able to spit all that good info out, not to mention the impressiveness of what one would need, in order to do what I need to do. I think we've used all the good info to make a decent compromise that involves a wall just behind the stove and range hood area with nice big openings on either side. That way we can use a reasonable range hood instead of this NASA stuff. Oy.

Weedmeister: a box up a little higher holding a vent insert is just what we are starting to think about... then the lights can stay and there'll be lighting over the stove top.

    Bookmark   February 26, 2013 at 7:38PM
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And I didn't even get to the UV filtering needed to deal with the grease above that immense register. :)

The lower you can put the capture aperture, the smaller it can be.

Careful evaluation of sight lines may allow the beam to be even deeper, allowing a lower hood that is still visually masked. Please keep in mind that in addition to effluent spreading all by itself, cross drafts also cause it to miss the hood aperture. These can come from windows, doors, and people just moving around, and are worse with relatively open island and peninsula range locations.

In general, some effluent/odor will escape immediate capture no matter what and the hood will then be performing house air changes until odor goes away. One tries to ensure that the amount of condensed grease is minor from such cases.


    Bookmark   February 26, 2013 at 10:07PM
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In my last house I had a Thermador telescope vent. I solved the the front burner lack of pulling by leaving a tilted cover (used a wood spoon) on the pot directing the steam, odors etc toward the telescope.

    Bookmark   February 27, 2013 at 9:07AM
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For 20 years I've managed the center downdraft in a cooktop island by same method described by eandhl above: tilt lids toward your downdraft---it works very well! 20 years and we have not had to paint ceiling nor seen any effects on upholstery in adjacent family room open to kitchen.

    Bookmark   February 28, 2013 at 2:01PM
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Yup, I had to make the same trade off on an island for a whole bunch of reasons. My solution was to use a Gaggenau AT400. ItâÂÂs a backsplash, not a downdraft and the difference is significant. It pulls the air across the cooktop about 10" above the surface then it pulls it down inside the machine. It works much better than I expected, and it carries a commercial rating but it's not cheap. Don't know if it's possible but if you can use the theory, it works way better than just a downdraft.

    Bookmark   March 1, 2013 at 10:16PM
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