Friedajune....Thanks for your response! My answers are below:

Since you've had this hood for a year, what has been your experience with things that smoke a lot like hamburgers or bacon - how did the hood perform for those?

The hood performed well when cooking hamburgers or bacon. I didn't smell the food odors from these items

Is this the first time you have cooked fish in your house? If not, how did your hood perform with those prior fish experiences?

This is the first time I cooked blackened fish or blackened anything. I typically bake fish in the oven and the hood does well to exhaust the vented air from the oven.

You didn't mention your duct from the hood to the outside. What diameter is it.

I looked back at my order and confirmed the duct to the outside is 8 inches.

The exhaust could also be hindered if there are a lot of turns in the duct before it gets to the outside, or if it is a long distance to the outside. Do you have any of those conditions with your ductwork?

No. The duct path from the hood is straight up and out the roof. My range is on an outside wall so this allowed a straight run without bends and turns.

Two things to consider:

1) is the hood performing well? especially in the area of replacement air (MUA, very leaky house or open kitchen window)

2) I found that after a high-heat cooking session, the baffle filters in my hood retain some smell and slowly dispense it back into the kitchen. Since then I took the habit of washing them right away under a stream of hot water - the fresh grease and gunk go away without scrubbing or dishwasher help.

My bet is on #2 above.

What goes out must be replaced or the house would implode. :)

You need to specify how restrictive the make-up air path is, as well as the hood exit path. This determines actual flow rate which will be well below the zero pressure drop blower rating, or even the zero pressure drop blower plus hood rating, where (rarely) supplied.

Required actual flow rate is determined by effluent uprising velocity and aerodynamic factors at the hood baffles, and indirectly by BTU/hr available or even BTU/hr used. What is the area of the aperture of your hood? For reasonably low pressure loss make-up air, gas burners, and baffled hood designs, the blower's rated zero static pressure CFM should be in the 135 CFM/square foot of hood aperture region so that at least 90 CFM/sq. ft. is obtained in real life with all pressure losses accounted for. And this assumes that the hood aperture does overlap the rising and expanding effluent (and a lot of guesses at undefined factors).

Any cooking products that are not initially captured and contained by the hood will escape into the room and potentially condense grease and moisture on the surfaces. Even without condensation, escaped effluent is only removed from the household air at an exponential decay rate based on the actual hood flow rate and household volume. A good sense of smell can work to very low concentrations of some chemicals, so because the remaining effluent is only decreased by 37% per time constant (household volume divided by actual flow rate) at full hood power, many time constants may be needed. And if wall, ceiling, drape, and rug contamination evaporation is also a factor, as it likely will be, than many more time periods will be required. This is why overlapping hood capture area, high hood flow rate, and adequate make-up air methods are important when dealing with cooking odor.

kas

Kas, how do I calculate whether the hood is performing at 90 CFM/square ft? The blower specifications should have what the CFM is at zero static pressure?

Seems like the horse is out of the barn unless you plan to rip the kitchen apart.

What I do is open a window or a door and start the hood before I start to cook. That creates an airflow and eliminates residual cooking smells.

Sometimes, the weather and humidity level can make a big difference. Or what I'll call the "mood" of the house because, while I understand it, I don't have enough science to explain it. Recently, I steam roasted a chicken. Something I do most weeks. Same way as usual. This time, however, there was something about the mood of the house that the whole house smelled like the chicken for a day or two. Usually, in the kitchen only, there's a faint odor from the pan sitting on the counter, for a couple of hours. The last one went up the stairs or through the ceiling and hung around for a couple of days.

Couple the mood of the house with blackened fish, and I can imagine your dilemma.

Before you start changing your set-up, why not try the basics? First, run the hood from when you start your prep. This is also a good way to make sure you have adequate air coming in. When my hood is running at a good clip, I can feel the air flowing toward the hood. This may also start sucking in the odors of the ingredients as you prep. It weirded me out at first, but it happens. Not completely, but it does.

The next thing is that when you make something like that, you should leave the hood running after. There's still a lot of smell in the air. If the blower is right there, and you're eating nearby, this becomes a trade-off between smell and noise.

I haven't tried Gigelus's immediate baffle cleaning, but it's a good idea. I'd say after cleaning the pots and putting everything away. That gives you a clear field, and enough time and coolth for the uck to settle on the filters.

No matter what you do, or how powerful your hood is, or how perfectly ducted, or how clean the filters, you're dealing with a very smelly dinner. Fish tends to be smelly--the odors in the air get smellier even if the fish itself doesn't smell fishy when you eat it. Blackening is beaucoup smelly. If you present your beautiful, glistening, steaming blackened fish on a lovely platter, you're carrying the odor around the room and into the dining room/area. Can't be helped. The smell is going to escape, and it can linger. It's happened to me with meals that didn't make the kitchen smell, but lingered in the dining room.

I'd say to try a few more things, a few more ways, being conscious of the positioning, ventilation and make up air, and see if you can make it manageable before you start redoing everything.

Aperture area is the area that is inside the inner hood edge at the hood bottom. the aperture area may be larger than the area that the baffle structures encompass. If baffles or mesh filters are more or less flush with the bottom, then aperture area is the area (including mesh or baffles) that the air is pulled through, but not including any large plate areas that might be used for mounting lights or whatever. In the case of VaH hoods, some eye-balling may be needed to decide just what area is effective in collecting uprising effluent.

So, for this simple approach to blower sizing, one determines the area in square feet, multiplies by 135 CFM/sq. ft., and declares this the desired zero static pressure flow rate. However, reasonableness in available make-up air, exhaust ducting, etc. is assumed here, and some cases may allow less, and others require more. But the actual flow obtained on maximum should be somewhere in the ballpark of 90 CFM/sq. ft. of aperture for gas burners, perhaps less with induction cooking.

When I have time I'll try to reference a source for this latter point.

N.B. Rising effluent that misses the aperture is not immediately captured and contained; this is true no matter what (reasonable) flow rate is achieved. At best it is removed as the air in the house is replaced.

kas

IMO, the CFM calculated based on BTU is only for safety reason, which only prevent high temperature accumulated in the cooking area. So one should consider this as minimum requirement. For near perfect odor extraction, CFM is almost never too big. The good thing is that if one calculate CFM is based 6 burners full on, then when he/she woks on one burner at full blast and runs the hood at maximum, the CFM may be just about right to extract the odor out of the house very well.

Hoods are designed to remove / collect two things ONLY

1) Smoke

2) Grease

Hoods are not designed to remove odors or Btu's.

Provided the smoke was removed during the cooking the hood did its job perfectly. The only way to prevent odor going through the house is to cook, eat and wash the pan under the hood with it running.

As noted above. As soon as you take your meal to the table and put the pan by the sink for washing the odors will fill the room.

Charon70.... I agree that what this and other sites promote as a benefit of a hood, and it does remove odors WHILE your cooking only. Realistically if your enjoying your meal at the dining table and your dirty pan is by the sink and the hood is turned off the odors are going where they want.

Provided your kitchen is not smoke bound and your furniture greasy I think your hood is working just fine.

Well, a hood can be designed to do whatever you want it to do within the limits of physics (or more precisely, fluid dynamics). Removal of most of the grease particulate spectrum and any non-grease particles composing smoke, along with excess moisture, are primary functions of kitchen cooktop ventilation. In the process, all odors that are entrained in the rising and hopefully captured and contained effluent are also removed. Obviously, if an odor generator is removed from under the hood, or the hood is turned off, then odor is not captured and contained.

The capture and containment process is aided by the uprising velocity of the cooking effluent and (where applicable) gas burner combustion products. A pile of room temperature cilantro on top of a cold cooktop will out-gas in all directions, and if either the air motion locally, or cilantro oil molecular propagation speed is higher than the hood air velocity at the cooktop surface (generally very low, even on full power) then one will smell cilantro throughout the kitchen. I might argue that is welcome, but other odors may not be so nice.

For eshmh: My velocity values are derived from peak thermal plume velocities as described by "Thermal plumes of kitchen appliances: Cooking mode," Kosonen, Koskela, and Saarinen, in Elsevier B.V., Energy and Buildings, and attempt to account for the effect of baffles on moderating the blower air velocity averaged over the baffle space relative to the peak cooking plume velocity shown in this reference. A similar velocity approach is one of the sizing methods described by Greenheck in their document, available on-line, KVSApplDesign_catalog.pdf.

Due to the necessity to capture and contain effluent from any burner when it impacts the baffles, even with the other burners off, the air velocity entering the baffles has to be high enough at any point under the baffles. Hence, we can design for one burner's peak plume velocity and achieve good capture and containment even if all burners are operating. However, the cooking plume velocity shape (measured transverse to "up") is rather like a peaked-up Gaussian function, and has significant width tails that may easily exceed the hood horizontal size at the hood height under some conditions. Capture of all the plume all of the time is unlikely with most space limited residential kitchen hoods.

Conversely, the total plumes' mass rate of rise with all burners operating will be less than the total mass air flow through the baffles from the hood blower so long as the velocity of the hood air is high enough to preclude peak plume reflection off of the baffles and into the kitchen. This is because we designed the velocity to deal with the peak plume velocities which exist over only part of the zone into which the plume rises. If the hood velocity at the baffles is too low, then reflection occurs at the baffles, leading to effluent spillage, as shown below.

(From CKV_Design_Guide_2_031504.pdf, (c) 2002 by the California Energy Commission.)

kas

Possible circular logic here due to needing unavailable data to reach an accurate answer, but the concept is this:

As a "given," you have a blower and some flow path restrictions. These restrictions include: baffles, hood transitions, ducting, roof cap (if not accounted for in the fan curve for a roof blower), and make-up air (MUA) pressure drop. (MUA drop can be measured by people with the appropriate equipment.) If you knew the pressure drops across the various restrictions as a function of flow rate, then the data for the combined set of restrictions could be used to construct a line on a graph that defined pressure loss (ordinate) versus flow rate (abscissa).

Now, assuming that you have the fan curve (flow rate versus pressure difference) for a particular blower, you can draw the pressure loss line on the fan curve. Where the pressure loss line intersects the fan curve defines the actual flow rate (x-axis point below the intersection) and the pressure loss at that flow rate (y-axis point to the left of the intersection). The air velocity average at the hood aperture is the flow rate divided by the aperture area in like units.

All of this hangs on knowing a bunch of pressure loss resistances, many of which are not specified anywhere, and one of which, MUA, depends on house leakage and/or design of your MUA system.

This is why I recommend a 1.5X factor to roll up all these unknowns into a likely adequate compensating value. However, unless you know that the house will leak air at the desired hood flow rate with only slight pressure drop (preferably less than 0.03 inches w.c.), then some added MUA path is either desirable (to get the flow rate you want), or essential (to eliminate combustion appliance back-drafting bringing carbon monoxide into the dwelling.) There are by now myriad comments in this forum on these issues, and allocation of significant search time here or in professional publications is recommended if you want to be informed.

I hate cooking odors unless it's from cookies. In an ongoing campaign to eliminate odors from my home, I have taken to throwing my Broan aluminum filters in the dishwasher at least once a week, and in the case of bacon, that day. And we cook our bacon in the oven. You also learn that it doesn't pay to leave dishes in the sink or pans on the counter. And I soak my sinks with chlorine bleach water once a week, in part to flush out the plumbing because drains stink too. My hood is 10 years old, and it's supposed to be on the quieter side, but we cannot eat in the kitchen with it on, like talking on the tarmac.

'Down south' some restaurants have a 'shack' where they cook the blacken food.