I take it you have a two story house?

The 24 inch distant is standard in exhaust gas vent line like in natural gas water heaters. Think a natural gas central heat furnace also. In these 2 cases there is no fan to move the exhaust this allows it to develop a bit of a velocity to carry it outside. I do not understand why this standard would be in a 1200 cfm fan system. They are probably following natural gas exhaust rules to avoid any conflict with a cityÂs rules in the install of their hood systems (since itÂs an exhaust gas). More or less calling for higher standards that what is actually needed but if they say thatÂs how to install it thatÂs how it has to be done to follow code.

The first time I spoke with Viking about this they said I needed the 24 inches and it was documented. After I questioned them a little further they basically took it back and then said that they have found the 24 inches to be necessary but it was totally up to me. I think it is poor that they have not informed their customers that for their product to work effectively the 24 inches is needed. Plus the 10 inch duct makes this hood not really usable by the average home owner if they want to install it correctly. Venting up through the second story and then through the attic is not an option. Also, just try knocking a 10 inch hole in you wall and see what happens to the joists above.

I spoke with Independent about this and they told me if I installed one of their hoods that required a 10" duct and I had a 90 deg turn very close to the hood... it would not work and would be very, very noisy, and that they basically guaranteed I would NOT be happy with it.

In the end I chose a Wolf Pro Island hood and am running it straight up through the upstairs bedroom through the attic to a rooftop blower.

I would follow Viking's recommendation or don't do it at all because I do not think you will be happy with the performance or the noise.

We have the Viking 1200cfm hood (with external fan motor). ours is installed with the 10" 90 degree elbow mounted right to the hood. The duct work goes through the exterior wall inside the 12" high cabinet that is above the hood. I my opinion it works just fine and the noise level is rather low. Even on the highest setting the noise is still no more than the fan on our old over the range microwave fan (though this could be due to the external motor).

For what it is worth ours was installed by Viking factory trained installers and is covered under warranty. I never noticed any stipulation about the 24" height requirement. Since I purchased all the appliances and coordinated the installation I read all of the manuals and never saw that.

OK, that is good to hear. Because we could not cut a hole below the joist we have decided to have some custom ducting made. Instead of using the 18x5 rectangular to 10 inch round transition piece and the 10 inch elbow we have decided to make a 18x5 rectangular elbow and save about 6 inches in height. Then we will use a steel lintle above this gaping hole and a custom damper on the outside of the house. I just hope we have the same results as ken after doing all this extra work.....

clax66,
Are you using an external 1200 cfm blower? Was their reasoning that there is turbulence casued at the elbow in the vacuum that impacts the hood performance, in which they prefer to have 2 feet of straight duct to even out the air flow before the hood? If you are using an internal blower, I can't see why it would matter, unless the close elbow causes more noise with the blower hitting the elbow with air.

I called Viking today and the person I talked to said that there isn't any 24" straight run restriction for the venting, the only restriction is that it needs a 10" duct.