Vent hood mounting height and duct shroud questions
As soon as the roof vent is installed, I plan to install a new vent hood which will replace the Faber Scirocco downdraft (which will remain in place - just won't be used as much). The particular model of hood (Vent-a-Hood NPH18 dual fan) has a suggested maximum mounting height of 30" above the cooktop.
This will be my second Vent-a-Hood - both of the approximate same basic design. The first came with my former house and I was happy with the height (unknown but judging by old photos appears to be ~24" above counter/cook top height and was probably 24" deep hood).
The difference now is that the old house had a slide in Dynasty stove which came out more than counter depth while this new house has Miele modular cooktops well within counter depth so we may have to get our heads closer in. The new hood is also 24" deep. I wonder if 30" hood clearance is adequate. We are right at average height for North Americans.
Somewhat complicating this is that we have a 15 1/4" high tile backsplash and then have a warmer shelf that is 14 15/16 or 14 31/32" high that will sit on top of this so the minimum mounting height will be just a shade above 30".
Old house - 24" above counter height?
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New house and cook space
The second question I have is the duct shroud. I'm not interested in the Vent-a-Hood shroud as it is a bit massive (36" wide) and expensive (pretty much a grand). I was thinking of a 12' x 12" custom fabricated shroud that just hides the 8" duct and electrical cable. How do I mount this? I was thinking of a flange down each side and screwing this into the wall. Would sturdy anchors do or would it be better to put in 2x4s behind the wall to hold it? Same for the warming shelf. No guidance from Vent-a-Hood.
Comments (9)
kaseki
5 years ago
opaone
5 years agoRelated Discussions
Can range hood + duct vent air out at point lower than stove?
Comments (3)Moving air through a pipe doesn't really car if if it (the Pipe) is going up, down or sideways. Sure up is always better because you gain the natural rising of heated air, but plenty of setups flow down. Where do you think the air in ALL downdraft hoods and JennAir's flows??? Re: remote vs. internal- either type will work AS LONG AS the selected unit pushes/pulls enough air (cfm's) to overcome the static pressure of your pipe and all the bends. Remote or inline ones are generally quieter than hood mounted ones....See MoreIs running vent hood ducting through cabinets OK?
Comments (16)I want to echo Weed's caution about being sure on code compliance when having your vent going out near that window. Last year, when I was doing a re-routed of the vent on my range hood, the local building inspector happened by. (We are on pretty good terms so there was no compliance issue.) I asked him about the rules and got a long dissertation as he handed vent tubing up to me. The gist of it was that the rules for range hood vents are different than for those that directly vent gas appliances (say a water heater power vent). There is some discretion when it comes to venting from a range hood over a gas stove. How far the vent has to be from an opening window also varies with whether the vent is above the opening window, at window level or below window level. I was told the vent that is above an opening window can be closer than one at or below window level. BUT, you want to be sure that, if you open the window while the hood is running, it won't be sucking in the vaporous stuff that was just blown out the vent....See MoreRange Hood Vent - Y duct adapter
Comments (11)OK, wok cooking: This requires the highest level of residential ventilation if you want all of the grease and water to be expelled instead of condensed on the interior. Start with capture. The plumes from pans expand as they rise. We believe that a good approximation for hood capture width is the cooktop width plus six inches. For a wall hood, the front-to-back opening should be wall to 3-inches past the cooktop (toward the cook). Lights and switch panels add to this, depending on how the hood is configured. Continue with containment. Given these aperture dimensions, modified by the reality of whatever products are actually available/affordable/aesthetic, and how the cooktop is installed in the counter, one computes the area of the hood entry area in square feet. Multiply by 90 CFM/sq. ft. (equivalent to an intake air velocity of 90 ft/min). This is the required or actual CFM. Multiply by 1.5 (if you don't want to do a complete analysis) to get blower-rated CFM, which is only valid when the blower is hanging in free air. Next is ducting: This is usually specified by the hood manufacturer, but the goal in cold climates is operation near 1000 ft/min, and otherwise in the range of 1000 to 2000 ft/min. This is given by duct sectional area divided by actual CFM. Don't forget noise: Best blower noise reduction is achieved by using a roof blower or in-line duct blower, with a silencer mounted between the blower and the hood. Silencers are about 4 inches larger in diameter than the duct, so silencer installation needs to be considered ab initio. Last, but really contemporaneous, is make-up air. MUA must be supplied such that the house internal pressure does not fall so far that combustion appliances, if any, are back-drafted. Some such devices, if not supplied with their own MUA, can be very sensitive. Even without such devices, one wants MUA pressure loss to be a small fraction of the cut-off pressure of the blower (top left of the fan curve). Review MUA related threads on this forum for more information....See MoreHood vent path using two duct sizes and venting down
Comments (4)The 4-inch duct was too small for the original plan. Probably an 8-inch would have been needed and then the higher flow rate requirement could be made to put up with a bit more pressure loss than is desirable . Air velocity in the hood ducting should be in the 1000 to 2000 ft/min range. Even if you only put a short length of 4-inch duct in a 10-inch duct path there would be very high pressure loss. (On-line calculators exist for these types of analyses.) And if you used a screaming mimi aerospace blower to get the flow rate at the pressure loss, the duct air velocity would be absurdly high and would try to compete with the blower for noise champion. Venting down and out may not be a violation, so long as your AHJ is OK with the details including slopes, sealing, and access, but such paths tend to be restrictive for various secondary reasons. And it seems you are limited to 4-inches in that direction, if I understood your message. I have no real picture of your kitchen, but if it were my kitchen I would use a 10-inch duct from the hood to the nearest exterior wall that didn't dump onto a deck or an openable window. I'd either enclose the duct with a soffit, or make it decorative. Alternatively the duct would go to a point on the ceiling where an upstairs chase could be added to get the path to the attic where it can deviate as necessary to get to a good position for a roof blower. For reference, I have seen images of wood-everywhere type structures where a hood duct went skyward across the room to the desired point on the roof. This appeared to be at least 20 ft high. Such schemes require stainless steel ducting to look decent. This wouldn't do if the ambience were not rustic. Can you extend the wall studs on the existing wall by 6 inches (cutting out 6 inches of space next to the cooktop) so there is space to have enough duct area?...See More- PRO
The Kitchen Abode Ltd.
5 years ago zneret
5 years agokaseki
5 years agozneret
5 years agozneret
5 years agolast modified: 5 years ago
"Finished" my installation today. I opened the wall and added in framing so that the mounting strip is held by 4 screws (the hood is held onto this strip by 2 screws).The roof vent (VentaHood, stainless steel I think) was rather easily installed as the roof has battens and spacing was wide enough for the hood to slip in between 2 battens and just replaced a tile. Straight up 2' from hood to ~65 degree elbow, 5' 10" to 2nd elbow (~85 degree) and straight out. All joints and seams metal taped and the ducting wrapped in insulation. Total vertical rise of ~6'.
The roof vent has a flap held down by a magnet. Was worried after reading threads here that the distance and curves were too long and the air velocity and force would be too weak. 1 fan at half speed lifted up the flap half way and full speed all the way. Totally pegged with 2 fans running at full speed. The vent is a PITA to use as the flange is too short (just 1" so screwing in the elbow wasn't the easiest).
Tomorrow, I will try making Cajun blackened chicken (Paul Prudhomme recipe) to see how well it works.
One other note, the vent doesn't come with a pest screen. VentaHood advises against using one but birds and wasps are nesting pests where I am. I fabricated and will try a removable one and see how that works.
Complication was that one of the lower screws for the warming shelf didn't hold (anchor failed) and the stainless steel flexes too much so I will have to open up the wall behind to add in a piece of framing.
I will figure out a design for a duct cover (most likely will suspend it from the ceiling) and get that fabricated.
zneret
5 years agolast modified: 5 years ago
kaseki