Get a large 54" canopy hood with at least 1200 CFM for over the whole cooking zone and just don't use the downdraft. You will get better ventilation for the rest of your cooking as well. Don't forget about the makeup air you will need to engineer as well. Or else you could be backdrafting your furnace or fireplace.

Thanks, hollysprings. I can't use a large hood because of the cabinets - the hood would block the cabinet doors from opening, and since we just remodeled the kitchen, I really don't want to change the cabinets.

I've included a picture of the peninsula and cooktop. The grill is the covered area to the right of the induction cooktop. To keep the area open, I am thinking of placing the hood only over the grill. I'll have to remove one of the lights above the peninsula because of the hood. The Dacor downdraft (in the down position in the picture) will vent the induction cooktop.

Hope the picture help.

Make sure that the hood aperture at the height (h) of the hood aperture above the grill is wider than the grill (each direction) by (at least) the factor 2 * h * tan(22.5 degrees). (If it were me I would extend it toward the cabinet door swing as far as feasible so I could fry under the hood.)

Take the resulting hood aperture dimensions, compute the area in square feet, and multiply the result by 90 ft/min for actual required cfm (for baffle filter hoods or clean mesh filter hoods). Multiply this number by 1.5 for duct losses, baffle losses, MUA losses, and transition losses. Find a roof or in-line fan rated for this final value at zero static pressure.

For background, read the references in my My Clippings.

kas

Thanks, kaseki. I have another question. I was in an appliance store today, and saw a Zephyr Layers Island 36 inch hood. The salesman said, the internal blower, right above the island, has 600 CFMs. If we get the inline external blower, it would be housed in the attic or roof, and with that distance away from the grill, we would go from the 1000 CFMs the blower produces, to an "effective" CFM rate of 700 since we'd loose about 30 percent of the blower capability. Do you agree?

A 30% loss would be about as good as you can expect, but when comparing the result to the salesman's cfm claim, it depends on what the salesman's claim was actually for.

(a) The Zephyr fan's rated zero static pressure is 600 cfm. In that case, the realized cfm with the entire hood and filter, ducting, roof interface, and typically limited MUA would likely be 400 or less.

(b) The Zephyr hood with fan rated zero static pressure cfm is 600. In that case, the realized cfm with the added ducting, roof interface, and typically limited MUA would likely be more than 400, but less than 600.

Case (a) is closer to your report of his wording.

An in-line or roof fan should prove less noisy, particularly if an in-line silencer is used. However, pre-packaged hood/fan assemblies will typically be less costly than remote fan systems when installation labor is included.

kas

Thank you for your advice. I am close to a decision and want to see what you think. I'm thinking of the 36 inch Modern-Aire PMI16-336 hood. It has a 1200 CFM internal blower with a variable speed. There's also the PSI16-336 hood. The only difference is the depth/height of the hood (horizontal "plate"). The PMI height is 4 inches, and 6 inches in the PSI. The other difference is the filter, but I can get the baffle filter in either one at the same cost. Do you think the PMI will work for my grill? And thanks so much for taking the time to answer my questions!

I generally favor hoods that approximate commercial units; however, given your choice, I would go for the higher/thicker unit as it should allow more uniform flow at the ends away from the duct. More uniform is not equal to uniform; in order for that configuration to be uniform in flow, the filter of whichever type has to be fairly restrictive so that the pressure drop across the central zone is sufficiently high to allow the flow at the edges to increase to a value closer to that at the center. This may not provide enough flow, so non-uniform may be better overall. Baffles won't gag very well anyway, thus supporting the idea that thicker will be more advantageous. I'm assuming that the fan is in the duct and not in the four or six-inch thick collection zone.

Note that an optimal duct to filter transition would be a logarithmic trumpet shape, just about as opposite to an abrupt transition as one can get. These units illustrate yet again that there almost always have to be compromises among aesthetics, cost, and performance.

Otherwise, go for a filter area as large as practical, as the filter in these units and not the boundary of the sheet metal defines the aperture area, which per earlier comments must overlap the cooking zone.

Baffles will probably be quieter than a mesh screen with 1200 nominal cfm across this size aperture (more like 800 with an open screened window).

kas

Yes, the fan is in the duct.

I didn't realize there was a functional component to the depth of the horizontal "plate" in the vent. If I understand what you are saying, we will get better smoke etc control with the vent that is 6 inches deep vs the 4 inch one. Either one would work, but the 6 inch one would be better. Correct?

Based on the pictures I have, the filter area is the same in both units and takes up almost the entire surface area in the "plate".

I've also looked at UTube videos of Modern-Aire and other vents in action. These probably were created by salespeople, but none the less, they were pretty impressive and looked like the Modern-Aire one described would work with our grill.

The air flows from baffle entry points to fan have to traverse their various distances in the space left between the tops of the baffles and the top of the "horizontal plate." This path should be less restrictive if the assembly is six inches thick than if it is four inches thick, all else being equal.

While smoke videos can reveal issues, a better approach is to use Schlieren photography to see the flow of hot rising effluent from a cooking surface. Schlieren photography allows one to view the structure of air that has a varying index of refraction due to local heating. It can reveal how much rising effluent misses the hood, and how much enters the hood and then escapes.

CaptiveAire provides some videos at the link for a 400F surface and 700F surface. Other imagery may be found by searching the web.

kas

Here is a link that might be useful: CaptiveAire Schlieren visualizations

Thank you, kas, now I think I understand. As others have said on this board, you are most helpful and I really appreciate your answers to my posts and others. I think I've read them all!

Then based on what you said, the best capture is with the upside down funnel hoods or other large, dome-type hoods, then a rectangle with some space for air capture (like the ones I'm looking at), and last the flat or curved glass or metal ones with no space to capture air before it goes through the blower. I realize there are other considerations like the size of the duct, blower, and dimensions of the hood, too. Just want to be sure I understand the hood configuration on venting.

Generally true, in practice, if the word "capture" is replaced with "capture and containment."

kas

Thank you, thank you, thank you.

I now understand the physics behind ventilation much better.

Once I have the hood installed, I will write a review and explain how a hood/vent decision is all about what you cook and the amount of smoke/fumes/etc that are created. What I didn't realize is, since we grill inside, and our grill is relatively large, we will be creating more smoke/fumes/etc, than regular range cooking, and therefore, we need a more powerful vent system than a downdraft can deliver.

Wanted to update anyone who may be interested on our outcome. We purchased the Modern-Aire PSI1630-336 model and it is fabulous! We are totally happy with our decision. Best of all, the hood looks OK in our kitchen.

There are two 600 cfm centrifugal force fans and they do a terrific job venting smoke and odors. I really like the infinite speed control. When on high, the fans do such an incredible job, that we had to have the spacers next to the baffles replaced - the fan would lift them. The spacers are now attached to the end baffles, so they are stationary when the fan goes on.

The noise level is about what I expected - it's a bit loud, but not unbearable on the highest speed, and most of the time we use it on the lowest speed, which is just fine.

We were concerned about lighting since we had to remove two of our overhead lights. I'm pleased to report the four lights on the hood do an excellent job, and best of all, they are on a dimmer, so you can control the brightness.

Anyone installing an indoor grill needs to be careful about ventilation. Based on our experience, only an overhead hood will do an adequate job. I don't know if you really need something as powerful or large as we installed, but we were not willing to risk another under-ventilated solution.

This post was edited by willaf on Fri, Dec 6, 13 at 15:29

Thanks for the update.

kas

Hi Willaf. I'm so glad I came across your post. This is the setup we are looking at with Modern Aire. We are looking at the PS16, which is the exact same model just the wall version. How do you like it so far?

We were skeptical on how the 24" cover (housing the 1200 cfm blower) would look on a 36" canopy but it looks good from your photo.

We are thrilled with the hood. It efficiently removes the smoke created from our grill, and as much as I didn't want a hood, I really like how this one looks in our kitchen. The fan is a bit noisy when it is on the highest speed, but that doesn't bother us. We wanted, and got, something powerful. With power comes noise, not unless you locate the fan on the roof, which complicates things.

Modern Aire gave excellent customer support, too. The fan is so strong, it lifted up the baffles! They quickly sent me a new baffle set up to correct the problem.

And i'm glad this information turned out to be helpful to someone else. I frequently tell the story of how we ended up with this hood, and I give credit to kas for helping me figure out the physics and what I needed.

Let me know if you have other questions I might be able to answer.

"We were skeptical on how the 24" cover (housing the 1200 cfm blower) would look on a 36" canopy but it looks good from your photo."

Willaf's photo also suggests how a more trapezoidal hood with short cover of the same overall dimensions might look in the same location. One just has to draw imaginary lines from the upper canopy corners to just below the intersection of the cover and the ceiling.

In any case, willaf, you are welcome.

kas

Hi Willaf. Would we need to specify this special baffle setup for the 1200 cfm motor when ordering with Modern Aire?

Also not sure if you are in the Los Angeles area, but curious to ask who did the hood install for you. We're in the process of getting bids for the install.

Thanks again.

I definitely would specify the baffles when you purchase your hood. I remember I could have either mesh or baffles. I think the baffles are standard with the one I got, but I wouldn't take it for granted. I also found customer service at Modern Aire to be really helpful. At one point they even connected me to one of the engineers. I wanted to make sure we'd be happy with the hood... no mistake this time...

Our contractor who remodeled the kitchen did the installation and he didn't have any problems. We hadn't had a hood before, so our installation included going through the roof for the venting. Unfortunately, he is ill and not working - plus we live in San Diego county. You might want to ask Modern Aire for contractor recommendations since you live fairly close to them. Our instal was on the expensive side since it included the roof work and drilling through our ceiling.