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?

You have already clarified the two dominant factors. It all depends on your tolerance for noise versus your tolerance for an "eye sore." My tolerance for noise is less. It is not necessary to mount a giant up-blast external blower (like restaurants use) on your roof; a centrifugal low blower of the type Broan, Wolf, Abbaka, etc. make is significantly less obtrusive. Or, accept the long duct run as an opportunity to install an in-line sound suppressor to make the hood reasonably quiet. For additional refinement, the fan curves of both internal and external blowers should be consulted for performance with different lengths of duct and bends. The roof fan can always be made larger to accommodate pressure losses, while the internal fan may not be so easily swapped. Bigger on the roof provides another advantage; lower noise at lower speeds where the internal fan might be running on high for the same flow rate. kas

A vent hood with the blower or fans inside the hood has is an internal system. An inline system is one where the blower is located in the attic or some remote location. The blower is mounted "inline with the ducting. An external system is one where the blower is also in a remote location at the terminus of the ducting, usually on the roof or on an exterior wall. Examples of inline and external systems can be seen at the Fantech website by clicking on the link below. Here is a link that might be useful: Fantech Kitchen Ventilation

I have no data or experience with any of these, but I have to speculate that a $350 power pack and a 1200 external blower are very likely not equal in flow rate, and that an external blower that had the same performance as the $350 power pack would be considerably less money. I have no idea what exactly a warranty is covering on a liner, weld failure? I see no functional reason why any quality external blower shouldn't be used with a liner given some match between the blower interface and the duct from the liner. I would expect that Broan/NuTone would sell something compatible. But given your plea, I suggest contacting Trevor. With respect to the quote: "Either an interior, in-line or remote blower may be used with Prestige hood liners and power pack inserts. Other blowers CANNOT be substituted." I am having a hard time thinking up an "other" blower option that is not one of "interior, in-line or remote." kas