A helpful plant would do it!

I'm in California. In 5 years, all plantings have to be 5' away from the house. Insurance agencies can make you do that now. So far, they haven't attacked foundation plantings, but they are making people cut down trees.

That exhaust outlet must be 3’ away from an operable window. You have to move it or get red tagged. Even though it’s ineffective as a vent, it moves enough air to also requires a Make Up Air system. And I hope to goodness the range isn’t in front of that window. I can’t take a trifecta.

Try not to cause further pressure loss by proximity to the ground or blockage from structures. Faced with this configuration I would consider placing a basement window well in the ground below it to increase the cap to ground distance to provide some relief.

Of course, the rated blower performance of 1650 CFM is far from what the actual flow rate will be, likely choked by downdraft intake aperture area, mesh filter pressure loss, and make-up air pressure loss, so ground interaction is difficult to estimate.

Given the obvious lack of second story complexity in that location, a hood system ducted to the roof would seem a better choice.

Blower specification sheet here: https://content.abt.com/documents/146340/SpecificationSheet-EB15-1.pdf. I think the Wolf version of this is the one I have on my roof supporting my Pro Island hood (over 10 sq. ft. of entry aperture with baffle filters).

C.f. intake aperture of D49M series downdrafts which use mesh filters (more restrictive than baffles). https://bestrangehoods.com/api/media/file/D49M_Spec_Sheet-8ff17dba-f480-46f0-bbb5-d1ae15eda452.pdf.

My conjecture: run this at full power and you won't have issues with free-loading guests.

Why on earth didn’t you do an overhead vent through the roof???

You’re on an outside wall. Why didn’t you install a real vent hood, instead of a nearly useless downdraft?

Range is on an island with a cathedral ceiling AND a beam that was in the way.

I don't see anything on the specs about proximity to the ground, or that it can't be under a window (the latter might be in building code but inspectors have already passed it). It is sucking and blowing air out, right, so a structure around it could reduce ability to push air out -- I think a screen on wherever air is blowing out would be preferable to a solid structure. I don't have a basement and Californians would lose their minds over a well window (I used to live in the midwest so I get it, but I think I'll just have to dig out a little area and line it with rock if that is needed).

Does it blow down, e.g. into the dirt? That sounds messy. And it would get the window awfully dirty. Ugh.

I didn't mean construct a basement window; but use a window well form to lower the local dirt level a bit. And this is only if there is actually significant flow being blocked. I still expect that for that 1650 CFM blower, you will be gagged to somewhere lower than 600 CFM. You haven't reported what your MUA plan is.

How was the 10-inch (suggested) duct laid under your floor? Is that panel in your photo covering a crawl space entry point that was dug out of the foundation? If there is still access to the ducting, you might consider a silencer from Fantech (FD-10 IIRC, 14 inches diameter for the 10-inch duct model).

A concrete step access to the crawl space would provide the increased distance under the blower that the window well idea was intended to provide. And I suspect code requires that the duct be accessible.

Zero reason than an overhead couldnt have been done. Ducts angle to go around beams all the time, and you just get a bigger duct shroud to disguise it.

Kaseki -- Slab was cut out for the duct, then concrete poured back in around the duct. No crawl space. Duct comes up in the sink cabinet and then to outside wall. I have a million pictures but of course not one that quite shows what I'm talking about.

Minardi -- yes it was possible to do an overhead but due to the height, it required a large structure to support it and would have looked terrible. I really wanted to keep the range on the island as I just love the ability to look out when cooking, rather than staring at a wall. Also, I lived in this house for 5 years with no overhead exhaust fan (just a 35 year old broken downdraft, lol). I knew that the downdraft wouldn't be perfect, but I'm currently living in a rental with a microwave over the stove/exhaust fan, and it is terrible. So I don't think I'll be too disappointed (I hope!).

What cooking appliances do you have?

How much do you cook?

Your current build has zero ventilation which can be a health hazzard for anyone in this house. It amazes me that the U.S. allows this.

If you are in a temporate climate and have lots of windows open all of the time then not much of a problem but otherwise it could be a problem that you should correct before continuing.

As much as you may not like the idea of an overhead exhaust coming down from your cathedral ceiling above your island, this is a functional health related thing, not a decorative thing. The health problems build up slowly over time so it's an issue of getting COPD or Cancer at age 60 vs not.

I won't pretend I know anything about California building codes, i.e., what is actually enforced w.r.t. the Residential Building Code, or what is piled onto it, but a buried duct can potentially accumulate grease, presenting a fire hazard -- not to the under-slab duct, but to combustibles near the duct ends. Clean out and/or inspection may be worse than awkward, in this case. But I'm not there so I am not going to speculate further.

For reasons associated with the nature of downdraft (side-draft in this case) systems, the actual amount of grease entering the duct may be small because capture of higher velocity cooking plumes is limited. Covered searing/stir frying may cut normal cooking plume upward velocities enough to allow entraining it into the horizontal flow of the side-draft assembly, in which case there would be some Cattura grease induction (and kitchen ceiling grease reduction).

I will ask, however, what duct diameter you had installed under the slab.

Someone has some redo to do. I can’t believe a competent contractor would have placed that there. So that leaves the assumption that the contractor was incompetent. And that leads to, ”what else did he screw up?”

Interesting, so if range is electric then no MUA required?

No, I think it means if you have any "gas, liquid or solid fuel-burning appliance" in the house meaning gas, liquid, or solid fuel-burning:

* Furnace

* Fireplace

* Range/Oven

* etc.

...then MUA is required

If the house is all-electric with no gas, liquid, or solid fuel-burning item, then it appears you do not need MUA.

"If the house is all-electric with no gas, liquid, or solid fuel-burning item, then it appears you do not need MUA."

That would be very ignorant. The harmful VOCs produced by cooking, regardless of heat source, is well known in the ventilation industry.

MUA should be based on required exhuast, not heat source. If you need 800 CFM of exhaust for an induction range then you need MUA or you are likely to have significant rot and other problems in your walls.

The MUA part of the Code is there to avoid back-drafting carbon monoxide from combustion appliances. As @opaone notes, there are other chemicals in the cooking effluent that one might want to exhaust.

MUA has other important aspects; opaone touches upon one in his last sentence. A sealed house with this 1650 CFM rated blower will have its interior pressure reduced by 2 inches of water column while moving nearly zero air. (See the specification sheet I linked earlier -- note l.h. curve intersection with ordinate.) (27.7 inches, w.c. per psi.) This will cause air infiltration through wall cracks, switch boxes, and other paths. One can get moisture in the walls and insulation dust into the house. And all this without actually removing the cooking plume. This is not a winning solution.

A passive MUA (damper and filtered ducted path from outside to inside) will probably be sufficient and safe enough with no combustion appliances. Alternatively screened open windows will probably be sufficient. But those who have to ventilate cooking when it is cold outside should have a heater supporting the MUA. Heating requirements can be derived from the graph below (click to expand).

NO, that is NOT what that means and it is clarified in the code that it involves the VENT HOOD, not the means of production of heat. Any VENT HOOD over 400 CFM requires MUA> Because a strong vent can pull air and dirt out of your walls

.

Thanks!

Thank you everyone!! I don't know if contractors have a MUA plan but they will be working on it now. I don't think this exhaust will pull anywhere near the 1650 but it's still well above 250 CFM. Luckily, we are in So Cal so doors and windows are open a lot of the time, but due to allergies, also closed up a lot of the time.

I posted this so anyone else looking at the Best Cattura Downdraft would have more information on the exhaust. Never thought it would generate this discussion. Great job community!

Kaseki it is a 10" duct. Can be cleaned out from outside, not sure about inside. The Best Cattura is widely considered the best downdraft out there, so I am hoping it is easy to clean, at least superficially. I always understood that a downdraft was not ideal, but honestly, we didn't use any ventilation for 5 years because it was would stop working after 5 minutes (it was a 1986 GE gas rangetop with a downdraft exhaust). The rangetop only had 2 burners, but it was barely noticeable that we didn't have an exhaust fan. Of course, now we know that is very unhealthy, but we had very leaky windows so I think we are ok. My 90 year old Mom has had mild COPD for years and it didn't get worse.

All that said, I never thought it would take me this long to get the remodel started and I'm glad I didn't think too much about the lack of exhaust.

In order for a downdraft (actually side-draft evacuated downward) to capture anything, its weak air velocity away from the unit' aperture has to exceed that of the cooking effluent. The only scheme I've thought of for realizing this for hot cooking is to cook somewhat covered so the upward momentum of the cooking plume is defeated. Covered means using a fitted cover, or a screen, or some foil overlapping the pan. You don't need the cover tight, but it needs to cause the plume to reflect off of it. Essentially, the steam/grease/etc. will end up with sideways motion or very weak upward motion.

This applies to induction cooking, where all heat emerges from the pan. Trying to zero the upward momentum of a gas-fired burner plume searing a steak would likely be infeasible, or possibly unsafe.

That was one poor design... go with a roof vent and call it a day.