heartsurgeon and cpovey, Thanks for the info. In March, after reading hours (days?) of hood information on GardenWeb, I had decided to get a VAH 42", 600 cfm (VAH doesn't make anything higher than 600 cfm for a 42" hood and 48" was too big). I had made a cardboard hood of that size and mounted above the cooktop (no cooking allowed!) to get an idea of sightlines. 32" was best for viewing across the greatroom for me, but the cook in the house was fine with 30". The VAH rep insisted to never go above 30", so we were set to go with VAH at 30". But, since there was a delay in the BlueStar cooktop we wanted, we waited. The housing market got worse and a large appliance place folded and liquidated their inventory, and I got a deal on a Viking that I couldn't pass up. The hood didn't come with a blower, so that's why I have been asking the blower questions. Since higher CFM blowers were available on the Viking, I thought I could push the hood up to 32" with higher CFM and be OK. I figured the internal motor probably has twice the noise...the air noise through the baffles and then the air noise through the squirrel cage blower. So heartsurgeon, it wouldn't surprise me that it's noisy when on high at 600 cfm. Do you even hear the motor...or is it all air? The external probably does look like the best option, as I agree with cpovey that an in-line motor would be a hassle to maintain. Looking at the specs, I think the external would fit on the roof. Cpovey, I don't know if I could install the external upside down either...is there a damper that would be upside down? I had been only considering venting out of the bottom if I used the in-line. If I use external, it would go on the roof. Now today when I picked up my hood, I scrounged around the warehouse and found that they had a 600 cfm internal blower left for that hood, which I able to pick up for a good deal as well...so I couldn't pass that up either. So I"ll start with a 600 cfm internal, mounting the hood at 30". If it end's up too noisy, it's not that much of a loss and it would allow us to find out if we need more than 600 cfm. If we don't, but want to use an external for noise reasons, we will still come out ahead cost-wise. I think I'll still use 10" duct work in case I do want to go up in CFM if we go to an external...it's not that long of a run, so it shouldn't cost that much more. Also, I would think that a 10" elbow above the hood would make less noise than a 7" elbow. I plugged the 600 cfm fan in (not inside the hood) to an outlet to see how noisy it was. It does make some noise, but it seemed less noisy when I added some wind resistance, so I won't be able to tell much until it's fully installed. It sure could blow some air when unrestricted though! This got me a little concerned that if the vent exits on the top of the roof...it will be only about 8 feet away from the deck table, pointing right at it. Will this cause an unappealing breeze to the outside dinner guests? Maybe the baffles cause enough resistance that it really doesn't blow out that fast in the real application? I am still interested to hear if someone has put an external fan this close to an outdoor sitting area and what the noise level is like. I'm guessing that it may just be a white noise-type situation outside?

Heh heh heh. This topic can be as complex as you are willing to tolerate. If you have the time, I have the material. Visit my My Clippings for links to relevant references that will provide background information. Review the near endless threads on this forum related to this subject. I don't have the time right now to repeat this material, but one key fact you need to internalize is that there are more restrictions to flow rate than just the feet of ducting, and these reduce the actual flow rate. So once an effective flow rate is determined sufficient to capture and contain the effluent over the aperture area of the hood, it should be scaled up by some factor (such as 1.5) to specify the zero-static pressure capability of the fan. kas

What type of cooking do you do? Lots of grease? Lots of onions and garlic? Lots of deep frying? I've had downdrafts, custom hood with insert, regular over the stove microwave with direct vent to outdoors (outside wall) over a 30" gas stove. The Micro over stove directly vented to outdoors worked great (micro over stove not my favorite). The downdraft JennAir with grill and downdraft worked great. The custom hood with insert was my favorite aesthetically, and vented through the roof and worked fine. I don't fry a lot of foods (less as time goes on), virtually never deep fry, and use lids a lot because I don't think anything keeps the smell of frying onions contained (just my opinion). Downdrafts seems to get a lot of pushback but the one I had was terrific. I think you can have reasonable aesthetics, reasonable cost, and reasonable effectiveness :) though perhaps not great :) But though we cook a lot (if guessing, I'd say more than 85% of the population) and microwave very little, I have never felt the need for super-high power and I don't like lingering odors. If I were doing a new kitchen, I'd do a downdraft because I really lean towards clean lines and more modern interiors. So, the bottom line I think is to consider how you cook, and if you cook lots and lots of greasy and odiferous foods on a daily basis, super high power performance might outweigh anything else.

Yes, indeed, the stove is on an interior wall. It would be simple if it were on an exterior wall, but a remodel to move it is out of the question. I am very happy with the current placement of all appliances and sink and storage. The stove currently vents down and under the floor out to an exterior wall. I will seriously consider induction, just wish I could get it with down draft. I have checked my pans with a magnet, and not one pan I have works, other than my numerous cast iron pieces. All the comments (especially the links that show the process) give me a lot to think about. I have to keep some kind of exhaust as I occasionally make a batch of lye soap. I hadn't thought about a portable coil for countertop, but it would allow tea brewing in the 2 gallon pot and would accommodate the steel pressure cooker. I am not sure I would trust the large heavy pressure canner on it. I could always visit a friend to can! Guess I would find out who my real friends are.