We also have a Zephyr over a 36" Bluestar gas cooktop. I did a lot of research about hoods and thought that I knew what I needed . . . I ordered one with 1200 cfm capacity and dual fans. I even called Zephyr and talked to their customer service techs before placing the order!
I should have learned more about installation - because proper installation is just as important as venting capacity and CFMs.
First mistake: The builder thought it would be OK to put 90 degree turns in the venting between the kitchen and the roof. Um, no, you can't do that or you will DRAMATICALLY decrease the efficiency of the hood. If at all possible, make the vent a "straight run" from the exit on the hood to your roof vent. If not possible, limit turns to 45 degrees, maximum.
Second mistake: The overpriced kitchen designer should have told me that it is crucial that your kitchen hood actually be larger that the cooktop. For example, for my 36" cooktop, I should have ordered a hood at least 6" wider. I guess these overpriced kitchen designers are used to planning kitchens for people who don't actually COOK in their kitchens . . . they just want them to look pretty.
Unfortunately, both of these problems are not easily or inexpensively corrected! Good luck and I hope this info helps.
You are correct about installation being at least as important as the hood itself. My hood is downdraft and the original was integrated into the cooktop. The new popup is at least twice as powerful as the old vent, and my first try bulged the understove piping. I ended up replacing the 90 angle under the floor with a plenum of my design, the 4 inch accordian flexible pipe with 6 inch smooth straight run ducts, and the original dryer type exterior cover with a screen cover. I now have the hood as the weak link, and a vent system that actually vents.
