nuppal we went with the Zephyr Venezia hood. We find it to be very quiet and does a great job. We have only had it about 6 months but we do a lot of cooking and the house is always smoke and odor free. The baffles are easy to clean.

Volumetric air flow rate (CFM) is determined by the type of cooking (and hence cooking plume volume and velocity) and the area that must be maintained at a velocity that ensures containment of captured plumes. For residential hood designs, I recommend 90 CFM/sq. ft. of hood entry aperture. Light cooking on induction might get away with 60 CFM/sq. ft. If your hood entry aperture is 3.5 ft x 2 ft (it should overlap in both directions) or 7 sq. ft. in area, then you would need an achieved/actual CFM of 420 to 630 CFM. Given pressure losses of baffles, ducts, and imperfect make-up air supply, I suggest a factor of 1.5 between required air flow rate and blower rated airflow rate, which is only achieved hanging in free air. So your blower ratings would be 630 to 1000 CFM. However, the above assumes a conventional hood, which this Zephyr clearly is not, judging from the images at the link. The actual intake aperture area is not the full width and depth, so the calculation and the capture effectiveness are not applicable. The overall width changes, but the area collecting effluent is the same between models, and there is no design shape to encourage plumes to get to the collection zone. It also doesn't use baffles, so so who knows what the pressure loss is. In summary, this hood is for decoration, and will not cope with real cooking except that eventually it will clear the kitchen (house) of whatever effluent remains in the air and hasn't settled out on walls, ceilings, and fabric. Is this quasi-hood intended to be vented outdoors?

Looking for a 30” ducted under cabinet range hood. Zephyr and Hauslane both seem to be decent brands and in our price range (<$400). Anyone have pros or cons with these brands?

A few comments: 1. Pipe diameter can be used to find the VOLUME or CAPACITY of the pipe. Saying a 6" exhaust duct, assuming round here, is half the size of an 8" is not correct. It has half the VOLUME of an 8". Remember grand school geometry pi x r-squared give the area of a circle. So the inference in saying the 6" is half the size really is referring to it's 2d AREA. 6" round exhaust hood has an AREA of 3x3x3.14159 = 28.2743 square inches of area 8" round exhaust hood has an AREA of 4x4x3.14159 = 50.2654 square inches of area. 10" round exhaust hood has an AREA of 5x5x3.14159 = 78.5397 square inches of area. When talking about exhaust venting for a grease carrying duct (which is what kitchen hoods are) ASHRE says a MINIMUM velocity of 500FPM should be used. This is also the most efficient velocity. Faster velocities are less efficient, require larger motors and do not capture grease as well, but are acceptable up to about 2000FPM. Lower velocities allow grease to condense and can cause fires, reduced capture and poor performance. So lets see what the velocities are for the 6" and 8" range hoods (We have to convert the are of the pipe from above from square inches to square ft): 700 CFM 6" - 700 / (28.2643/144) = 3566 FPM 8" - 700 / (50.2654/144) = 2005 FPM 10" - 700 x (78.5397/144) = 1283 FPM 12" - 700 x ( 113.0972/144) = 891 FPM 14" - 700 x (153.9379/144) = 654 FPM 16" - 700 x (201.0617/144) = 501 FPM So as we see above the CORRECT duct size should be 16" for a 700 CFM blower to achieve the ASHRE recommended 500FPM minimum velocity for a grease carrying exhaust duct. This would also be assuming the duct run is very short and has minimal to no friction losses due to it's short length and no bends. If the run is LONG or has a lot of bends then there will frictional loss in the pipe. These losses are fairly well defined based on pipe size and length and can be found online with simple searches. If the exhaust pipe is not round then the math for area is simple, but the frictional loss calculations become more complex. There are charts to get a rough estimate. When running the fan at LESS than it's maximum speed then we need to figure out the correct duct size to achieve 500 FPM. Keep in mind that this will mean that we will have a higher FPM through the same size duct when running at a higher speed. To do this calculation we need to know what the total static pressure the hood fan is capable of achieving. For Zephyr models they list the total static pressure as 1.25 w.g. at the specific hoods maximum listed CFM. Static pressure is the resistance to air movement. This could be from restrictions in the exhaust pipe, lack of available air to put in the pipe, etc. This is where make up air (MUA) comes into the picture. Some new homes are built with a vapor barrier (tyvek or plastic sheet) that "seals" the house so well that air does not leak in around windows, cracks, etc. If an exhaust fan is running it is removing air from the building. When this happens the air pressure inside the building goes down. The exhaust fan has to work harder to continue to move more air. Once the pressure goes beyond the design static pressure for the fan the air flow slows down. In commercial building a MUA unit will have a fan and a way to heat or cool the air. This unit is controlled by a static pressure sensor that meaures the pressure difference between the outiside and incide the building. When the pressure drops inside the building the MUA fan speed increases to supply more air and equalize the pressure. In a home the MUA could be opening a kitchen window. When the exhaust hood/fan is on the make up air will be drawn in through the window. Or a system, like what a commercial building uses, can be installed. NOW all that explained we want to know what the correct duct size should be for a Zephyr hood that has multiple speeds. I will use the Typhoon model. It has a CFM range of 250-850. Duct Size (FPM) CFM 6" 8" 10" 12" 14" 16" 250 1273 716 458 318 233 179 850 4329 2005 1558 1082 795 608 So what did we learn from the above chart? For this particular hood we should have at LEAST an 8" duct, but I would argue that a 10" duct should be the minimum. The max working static pressure of most Zephyr hood is about 1.25" w.g. That works about to about 1500FPM in duct before the fan runs out of oomph to push more. Add in bends or other restrictions and 10-12" would make the most sense. Now if you you are venting directly out the back through the wall and there is no real ductwork, then all of these numbers can go out the window as there is not realy duct to worry about.