Homemade downdraft vent?
Tim_789
12 years ago
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12 years agoCloud Swift
12 years agoRelated Discussions
Is ANYONE happy with downdraft ventilation? (allow me to vent)
Comments (73)We had a Thermador range with an integrated downdraft for about 14 years, in the peninsula. I liked the arrangement so well that we kept the location of the stove, refrigerator and sink for the remodel. We also kept the Thermador to use in the new kitchen. That was not a good idea. The stove had problems almost immediately when it was reinstalled. The downdraft was doing fine. Now we had a real problem. We had to replace the stove, but finding one that would fit was a problem. That wasn't the biggest problem for us. We thought we were going to have to install a hood. Our kitchen is at the end of a long room and I remember how I hated the overhead suspended cabinets that were in the original kitchen. I just didn't want something hanging from the ceiling and destroying the view. Since we are old, we wanted a range with a self cleaning oven. It was hard to find one with our specifications that would fit into the space designed for the new kitchen. We bought a Dacor range with a Dacor downdraft. These are separate units. I love the range and the downdraft works perfectly, for us. Long story to get to the point. When the new stove and downdraft were installed, the installers left the vent pipe with the opening upside down on a piece of wood under the house. That mean the downdraft did not work correctly. We could not figure out the problem, so my husband crawled into the crawl space and took pictures. I guess they figured old people would never figure this out. We had to hire another company to redo the venting. They took the vent pipe straight out to the side with no turns. It works perfectly. It even vents the steam from my rice cooker that is on the counter next to the stove. My point is that if installed correctly, a downdraft works....See MoreDowndraft vent dilemma
Comments (25)For a ceiling hood to be effective requires excessive aperture size, containment volume, internal baffling and CFM's. Otherwise they are only slightly better than downdraft. They are nirvana for open plan commercial kitchens but the install cost is about 5-7x the cost of a standard hood and operational cost about 3x (in cold climates) so are very rarely installed. The effluent plum at the ceiling is quite different than at 3' above the range. It is cooler and much less dense which works against good capture and containment. Closer to the range the heat of the effluent helps to contain it in the hood (hot air rises) until it can be exhausted. Even just 3' higher the byproducts that you need to exhaust are less dense by a factor of about 4 (so you have to exhaust 4x as much volume to exhaust the same amount of particulates) and it has cooled resulting in the need of nearly twice the containment volume....See MoreNXR range hood vent into existing downdraft
Comments (33)It is the velocity of the rising and expanding cooking effluent plumes that determines the velocity of the hood air needed to entrain the effluent into the baffles. One burner cooking at the vapor point of peanut oil, grape seed oil, or just grease will have an upward velocity of the order of a meter per second. With residential style hoods having minimal reservoir volume below the baffles, this effluent needs to be immediately entrained into the baffle flow. Commercial hoods with large reservoir volume can average out the plume(s) over the baffle space and operate on lower CFM depending on cooking conditions. See figure 4 of https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf Velocity of hood air integrated over the hood aperture determines the CFM being moved. Multiplying 90 ft/min times the hood entry area in square feet and multiplying the result by 1.5 to make up for not doing a proper pressure loss analysis (assuming decent MUA) will yield the rated zero static pressure flow rate (CFM) of a suitable blower. Hood entry area should overlap the burners in both directions -- side to side and front to back....See MoreFlush Ceiling Mounted Vent vs Downdraft
Comments (1)A wall location is much easier to accommodate cooktop ventilation than an island or peninsula configuration, but the extent of this truth somewhat depends on what is above the ceiling, and what the ceiling height is, and whether this is new construction or a renovation of existing architecture. The higher the hood entry aperture, the larger it has to be. Conceivably, with an 8-foot ceiling, a one-foot high assembly based at 7-feet height might be feasible. It would have to be commercial sized in its entry aperture (say 6-inches of cooktop overlap in all directions -- 3 x 4 over a 2 x 3 cooktop). In such a case, it could still have proper (albeit low angle) baffles and a containment volume above to a duct to outside. Cleaning would be more difficult with a hood base 48-inches above the cooktop than with a hood base 36 inches above the cooktop. I am not aware of any such hoods provided by the higher-end residential hood manufacturers, but am confident that if suitably encouraged, a tailor-made (bespoke) hood by ModernAire, for example, could be fabricated. You would still need a path to the outside, either through an attic, or chase in a room above, or horizontally if the joist heights provide sufficient sectional area. Twelve-inch duct might be needed. With sufficient floor stiffening, a deeper hood could be inserted into the joist space (in new construction) by framing out the area and providing a horizontal feed to an appropriate joist path. With additional height, baffles higher in the assembly could be used and potentially modestly less CFM would be needed. However, vertical ducting is greatly preferred, and avoids the potential for grease accumulation. Please be aware that the higher the hood entry aperture, the more susceptible the rising and expanding plumes are to transverse drafts, and even turbulence from people moving about. If there is a static direction of flow from air conditioning, for example, some growth over my 6-inch comment may be needed....See MoreMichelleDT
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