Many thanks for the suggestion. That was my first choice initially and I was going to purchase the vent reducer adapter (3 1/4 x 14 to 3 1/4 to 10) until I found out the adapter would significantly reduce CFM and increase sones on the 661. I cannot alter the vent size or shape, and thus am stuck with a 3 1/4x10 vent.

When we were looking for a hood 3 yrs ago, we went to a display which had an Alure III Broan and a Vent-a-Hood of same size and supposed capacities side by side. We turned both on and observed the sound. We bought the Broan. Then I found that it had been blackballed by Consumer Report that year. If I recall, they didn't like its sucking power or something. Nevertheless I am glad we bought what was supposed to be the quietest undercab vent hood on the market at that time. Manufacturers give you "sone" ratings which you can use for at least some kind of comparisons and that's what we used for our shopping criterion. We have problems with deafness. We know that we won't turn on a loud vent hood at all unless the need to vent is overwhelming. But the Broan Allure III has a very low setting which DH cannot hear at all (but I can). We use low a lot--for general "air out the house" as well as for capturing the steam when the oven is running or for a slow soup simmer and such things. I can hear the telephone ring and I can hear the person on the other end of the phone while this setting and the one above it is running. Usually I can understand the radio and t.v. also but the second, or normal setting, may be too loud for conversation or phone or t.v. sometimes. I use it for boiling noodles or tea water. The third setting is high. It is very loud for us. We use it when we need to deal with frying. We can stand to be next to the unit but it's not our favorite setting. Then, there's the 4th setting: Boost! That one is for extra strong suck. I have to leave the room sometimes when we're venting smoke and such because it's so loud. One of our favorite features is the "10-minute and then it's turned off" button. We can leave the room when fan is noisy and we don't have to worry about trying to remember that the vent is running. There are 3 settings on the hallogen light. We didn't like buying a hallogen unit because you can burn yourself on the bulb but after the first burn you train yourself fast in how to keep safe. It has 3 intensity settings. Filters are small enough that they can be put into dishwasher on the edge of the rack. They fit into a double sink basin, standing up. We planned to put a 90 degree angle into our pipe but there was a snafu (code won't allow venting into sidewalk area alongside driveway) so ours has straight up pipe through attic into roof. The model is notoriously difficult to install. I don't know if an Allure III Broan is even on the market any more. I think that the model class above it in pricing may also have low sound ratings. Elite maybe?

And the saga continues....HVAC man came by. looked all around, house is not tight but current state code is requiring MUA above 400 or 600 CFM, but enforcement is varying town by town. The town 3 miles away is rejecting permits without MUA. My town is not. He said given location of furnace and if I absolutely promised to crack a window, he'd be ok with no MUA. If the plans get rejected because of a lack of MUA, a simple unconditioned system could be put in through the crawl space at around $1800-$2500. That is of course if I get rid of the infestation of the biggest crickets he has ever seen in his life that are presently residing the crawl space. Still haven't connected with Kitchen consultant.

Where duct equivalence is a requirement, two 8-inch ducts could be used to match a 10-inch duct. In any case, searching this forum should have led to commentaries on determining requirements before picking hoods. Decide how much cooking plume effluent you want to capture by how much the hood overlaps the possible cooking pans and locations. (Assume a 10-degree from vertical plume spread.) Then use the area of the resulting hood to determine needed air flow rate when performing hot cooking (even if it is on only one burner) by multiplying the area in square feet by 90 CFM/sq.ft. Then, for the case of going directly out the wall with free air flow MUA, assume a factor of 1.3 for baffle pressure loss. This will raise the rated CFM needed for the blower by 1.3 such that the rating should be 1.3 x 90 x area in sq. ft. (Note that this is less than the 1.5 I usually suggest for normal duct lengths, less than perfect MUA, and a duct silencer.) If the hood or insert is a VaH without baffles, use 1.1 to compensate for minor losses such as from the outside cap loss and imperfect MUA. Example: 45 ft x 2 ft = 9 sq. ft. Desired flow is 9 x 90 = 810 CFM. Rated flow for conventional baffled hood then should be 720 x 1.3 ~ a nominal 1000 CFM. While equal blowers mounted in the hood or just outside via a minimal duct length will have roughly the same noise, outside mounting may allow a larger blower that one can run at less than full speed. This will greatly reduce blade tip turbulence noise, which otherwise dominates. Abbaka and Wolf and Broan, for three examples, make down-roof radial blowers that should be adequate to mount on a wall. Exterior aesthetic considerations may influence inside vs. outside, but a low pressure loss cap will not be much larger than a motor housing, and you get a damper with the housing.