I'm somewhat at a loss for words on this, because I haven't yet divined why Gagg would require a griddle plate for updraft ventilation but not for downdraft. Maybe I"m mis-reading griddle plate and what they want is to limit rising heat to avoid overheating _their_ pop-up overhead device. A normal hood at 30+ inches above the burners should not have a heat problem. I wouldn't use a naked back wall with a griddle, though. Tile or stainless steel would provide some safety margin. All that aside, hot cooking effluent rises at a significant velocity. To capture and contain it it with a down draft system is difficult and requires far more air flow than is likely to be present, or even feasible given the aperture sizes in the photos. Turbojet acoustics would follow. The pop up unit gets above the cooking (only one side at a time), but from its apparent size will have poor capture, and then the diversion to down flow via a very small duct will greatly limit the air flow rate. . The NuTone 10-inch fan placed in the wall above the cooking zone performs a kind of side-draft function. I would expect it to be better, but far from ideal. A lot of rising effluent will pass it, unless it is inside of some kind of overhanging hood. Note that without any filtration, the outside wall will be "washed" with greasy smoke and moisture. An overhead hood with mesh or (preferably) baffle grease capture that exhausted through the wall to an exterior fan would be preferable. A modest exterior fan (of the "upblast" style (but not restaurant size) mounted horizontally) would keep the effluent off of the exterior wall. kas

Carolml, I was looking at hoods at Purcell-Murray the other day because we too put a remote blower on the roof. I love the look of the glass canopies, but I was told that if the blower is a strong one (which ours is and which I suspect most remote blowers would be) you can't use glass because it will fly apart from the vibration. I don't know how much vibration there would be (doesn't really sound right to me), but.... that's what I was told. OTOH, my contractor thinks it would be fairly easy to just remove the blower that comes with a hood and connect the canopy to the vent from the remote blower. For me, the deciding factor was the mesh screen vs. baffle problem - we're going for quiet. Posts here at GW suggest that baffles are quieter than the mesh screens, and none of the glass canopies can be got with baffles. HTH, Burntfingers

First, hood size should be selected to assure capture of the rising effluent, which expands as it rises at about 22 degrees half angle from the entire hot pan surface. While an induction surface is relatively cold, the effluent you are trying to collect comes primarily from the hot pan. So a gas surface just adds additional rising heat because some of the heat generated misses the pan. Second, choose a cfm that for the hood design selected assures containment. This is vastly easier said than done, but essentially you want the velocity of the air entering the baffles times the area of the baffle portion to be at least that of the rising effluent, about 3 feet per second. Even better would be 3 ft/s at the hood aperture, particularly if the aperture is a flat surface with a mesh filter. Or, you can guess and say that for serious cooking you will probably want at least 600 actual cfm. Note that this is the cfm achieved when all pressure losses are accounted for on the fan curve (cfm vs. pressure loss). Given baffles, duct transitions, negative house pressure without good make-up air, etc., you may need a 900 cfm rated fan to actually get 600 cfm. Next, size the duct so that the 600 cfm that is being extracted from the house has enough velocity to minimize particle and vapor deposition on the duct walls. This is at least 500 feet per minute for warm ducts, and at least 1000 fpm if the duct passes through a cold attic during part of the year. kas

@3onthetree Okay, that makes sense. I hadn't considered the pressure issue. But this is an insert that is designed to be put inside a cabinet or frame. And I have seen a lot of these ductless inserts placed inside frames like mine that are against the ceiling and with cabinets on either side and no visible vent at all. So are they all installed wrong? I have watched so many tutorials and read so many blogs and no one addresses this issue. What if we create a top out plywood with a hole, then install a duct that goes up through that hole to blow the air out of the top? That way I could still enclose the frame and I wouldn't have to worry about dust collecting in the cavity, but the air would have some place to go. Would that work? Here is a pic of what the unit looks like inside the frame: