First which is more important, stove top or oven cooking? If you do more of one than the other, that is were you should concentrate on the best scenerio. Second, from what you have posted, it appears you cannot vent outside. If this is correct then consider an induction cooktop. It is more efficient than traditional electric and gas. It is faster than gas but doesn't radiate heat around your pan. You pan IS the heat source, so you are not venting out as much heat as you would with either of the other two stove tops. Electrolux, Bosch and Diva have great 30" tops with good size burners. Most of the other brands offer a good selection in 36". Downdraft ventillation is better than nothing, but you fight science. Heat travels up and with it goes smoke, grease and smell. A downdraft is limited.

Thanks for the response, but I am afraid I didn't make myself clear. The blower unit is an exterior fan, 1500 cfm, and it is the fan unit that is 30" by 26". I want to mount the fan on the roof. It does have a 4" flange all around it. I want to build a box on the roof that the fan will sit on, hence the plywood box. I need to find out how to weather-proof the box, and seal it where it sits on the roof, and where the fan unit sits on top of it. gammyt - I do not mean a range hood. The range hood will be inside the house, with a 10" duct going through the ceiling and into the fan on the roof. I will be cutting a 10" hole in the roof for the duct. sierraeast - its not a cap, its a large rectangular blower. Luckily my building dept doesn't care about range hood venting systems (except they do care about downdraught systems) Hope this make things a bit more clear

Thank you Cpartist. That is what I meant to say (instead of move the cooktop). I just think that is too much renovation for us at this point in time. Just looking for a little freshen up. Kids are almost ready for College and my discretionary funds are being diverted elsewhere other than my kitchen!! We will have to make do with the cooktop in the island but after these discussions I am leaning towards getting the best downdraft I can fit in my space. Although in all fairness, I rarely use the downdraft that I have now.

You seem to be on the right track. As far as I have been able to discern from their literature, the Abbaka roof blower is appropriately conceived. (I don't have one, however, to confirm this.) The silencer will be helpful. I am unclear what you mean by the liner moving significantly more air. The roof blower fan curve and the hood aperture baffle system pressure loss vs. flow rate will be the first determinant of air moved. MUA pressure loss will be the second determinant. Do you by some chance have hood pressure loss vs. flow rate data? Ah! I see Fantech list 750 CFM for this liner. But their liner is only 18 inches deep, of which about 5 inches is lamp bezel. Their flow rate limit is probably determined by noise and pressure loss. The Abbaka liner is deeper, front-to-back, (22 inches overall) and the bezel area smaller. I would go with the Abbaka, given I'm using your wallet. Best would be at least 24 inches, front-to-back. By the way, a 40 x 20 actual aperture (5.6 sq. ft.) requires 500 actual CFM to achieve a desirable 90 ft/min air velocity. Can I assume you aren't planning on running a char broiler that would require a higher flow rate? 500 CFM can be achieved with a HYEX-1.4 at 1.4 inches of pressure loss, and by the HYEX-1.0 at around 1-inch pressure loss. These values should significantly exceed the hood baffle pressure loss at that flow rate, but it would be good to get some data on that from Abbaka. In either case you do not want the part of this pressure loss to be MUA pressure loss. Plan on an MUA system. It likely can be passive if you have no combustion appliances. In other words, do not plan on achieving 500 CFM by overpowering your house leakage. Please specify what combustion appliances you have and whether you want a fireplace to work when the hood system is running.