You can not vent a pro style range that way. The required 8”-10“ vent pipe snd 42” vent hood needs to go up and out the roof. Or up and to the side, and out the house. Or you need to get rid of the high heat gas effluent producing range. It isn’t safe without proper ventilation. NXR has a short lifespan as it is, and youll be replacing it before long anyway.

The range hood is 36 inches. What are the other options we have in this case?

Would it make sense to go with a lower CFM range hood?

IMO get someone who actually inderstands how vents work Wahy can you not vent another way maybe show us the whole kitchen and also what is in the space above this wall.

You either vent to the physical requirements of the range, or you get rid of the range. You don’t halfass not even really vent it and endanger your family’s health. Ventilating it properly is part of the whole package of owning a range like that. You can’t ignore half of the equation.

The wall above the kitchen is the floor of guest room. Currently we have the downdraft of the existing stove going from the ground, to the left side, on the outside of the house. It is the nearest way to vent outside the house, from the left side.

Then you go up and create a chase through the guest room and yo the roof, or you go up and left through a soffit or through the upper cabinets to the left. Pick one, and make it happen. You're not using a too small and completely useless downdraft duct with the 42” 900 CFM hood that that thing needs.

Here’s the layout of the kitchen for our model. the vent from the downdraft is outside that window, on the bottom by the deck. Behind the wall is the formal dining room(with a drywall through which the installer was planning on running the duct & connecting to the existing downdraft). Above the ceiling is the guest room

Up and left is easy to make happen. An 8” duct fits inside the upper shelf of the cabinets quite easily. Thats a pretty simple thing to make happen, with the right contractor on board.

Verbo - thanks for all the information, I’ll find the right contractor to do that. I’m glad I asked here first

Verbo so running the vent through the upper shelves of the cabinet can be done easily by keeping the cabinets? we’re okay getting rid of the cabinet above the cooktop but was wondering how much damage we’ll have to do to the caninets on the left to run the vent?

Yes you can keep the cabinets, and just run the duct through them. This is done all the time. Sawdust happens when altering cabinets, just like omelettes require breaking eggs.

Find the right GC who works with a cabinet maker, HVAC pro, electrician, and carpenter. You need all of those specialized trades involved. This is only simple with the *right* pros, under the coordination of the right GC. Incompetents need not apply.

Thanks so much for the great idea. What type of contractors do this type of skilled work?

Find the right local licensed and insured general contractor.

Just to back-fill a bit: The potential in-wall (unless the wall is very thick) rectangular duct would be restrictive, the path to the outside used by the down-draft would likely be restrictive, although in that area one might expand the duct, and the U-turn in the wall from the hood would be particularly restrictive. Potential grease issues in such a duct are another problem. It is best to always go up, second best is up and over.

Whether one has to penetrate a series of cabinets to reach the outside or can use the space in the second floor joists depends on the joist direction. Did I miss that being defined?

You appear to have significant space above the cabinets below the ceiling. In case the joists run in an inconvenient direction, a soffit could be used for horizontal ducting, minimizing or avoiding any cabinet ravaging.

That photo is not your kitchen? Can you post a photo of your kitchen? If you have the same space above your cabinets, then that could be a good option so you don't give up cabinet space.

What about make-up air? Many jurisdictions will require that, too.

Here is the picture of my actual kitchen. We have some space between the cabinet & ceiling

You can convert from round to rectangular, run on top of the cabinets, and not have to cut your cabinets.

And an electronic nail finder can find the joist wood underneath (above) the sheetrock.

Verbo- do you mean run a rectangular duct from on top of the cabinets or through the wall on top of the cabinets & out to the left? We had a contractor come in today and he suggested running it from that wall between the cabinet & ceiling and out left.

So we had a good general contractor come over today. He said if we want to install a 1000 CFM range hood, then he highly recommends putting in a make up air unit from a long term standpoint. If we don't want to go that route, then he said we're better off going with a range hood of 400 CFM or less. He also said without the make up air & a strong 1000 CFM range hood, we'll run into issues with air from the doors & windows and just overall pressure on our hvac unit. The quote for installing the make up air unit is obviously double so we're thinking of going with a 400 CFM range hood. He can easily vent to the left by going above our cabinets.

Now my question is, is a 400 CFM unit efficient?

That is not even close to being sufficient ventilation for your range choice. If you want a consumer grade 400 CFM hood, the range needs a big downgrade to being consumer level range too. Get rid of the pro level ambitions if you’re not going to support them properly, with the proper infrastructure. One requires the other. They go hand in hand together

Verbo - if we don't have more than 2 burners(30,000 BTU at any given time) going on at the same time, do we still need a more powerful range hood?

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.

Yes. You need the hood and the MUA BOTH, based on the range choice. It doesn’t matter how many burners you plan to use on a regular basis. What matters is the capability of the range in total. It’s like owning a sportscar that you only drive at 60 mph to work. Your insurance is still going to charge you a premium, based on what the car CAN do. Because no one can resist that temptation.

Verbo - if we go with a cooktop that puts out 48,000 btu, can we install a 600 CFM range hood without MUA? The contractor said the exception to installing a 600 CFM & stay compliant with VA code is if we have 1509 square foot area which we we. So will going down with the BTU with a different cooktop(4 burner) allow us to eliminate the MUA?

You are going yo need MUA, period. And the threshold is 400 CFM, not 600. And has been since 2008.

Verbo - so the only way to go without a MUA is to swap out the cooktop and go with a less than 400 CFM range hood?

Yup. Low BTU low level consumer grade products is the only way that you avoid needing high CFM hoods and MUA.

Ummm. I would rephrase that to read: Low CFM hoods are the only way that you can escape the code compliance requirement for deliberate MUA, but not the necessity to have sufficient MUA to make the hood operate well. The code in this respect does not care about the performance of the cooktop. A 1950's electric coil cooktop could easily flare grease and steam or burn the contents of a pan sufficiently to require more hood performance than most would have had in those days, or even that of a modern hood that only had a 400 CFM rated blower (probably capable of 200 CFM when operating on house leakage MUA).

Kaseki - Sor Sorry I dont understand. You’re in agreement with a MUA being necessary for 400+CFM range hood?

Unless your house resembles that below, then when your hood tries to pull 400 CFM from house leakage, it will do two things, operate at partial flow rate due to flow resistance and also pull dust and/or moisture through the walls. Better is to have a duct somewhere with a damper that will open when the interior pressure drops. You could, of course, just open a window. If you can feel air from around wall switch cover plates, or the hood performance differs significantly with a window open vs. closed, some deliberate MUA is desirable.

Again, no air leaves the kitchen via the hood that isn't replaced in the kitchen by some MUA path, desirable or undesirable. If you seal the house you seal the hood.

Bali. See also traditional Samoan architecture.