Well, the devil's in the details.i would : get a hood, properly install it. then see how it works. go from there.
you may be over thinking this.
I just thought I'd mention, at our getaway cabin the range is on an exterior wall. There is a 12" through-the-wall exhaust fan directly above the stovetop and under the hood. Even that doesn't stop the smell from stir-fry, sauteed garlic, etc, from quickly filling up the entire joint.Our typical Whirlpool gas range sits in our condo's kitchen against a 4" interior wall. There's a microwave above the stove with a recirculating fan system that speeds up the time it takes to stink up the place every time I do a stir fry or sautee some onions.
Yes, I called Broan/BEST (same company) tech support at least 3 times. The first two times I was told that my installation was possible, but not recommended. Today my sales rep forwarded an email from the Broan regional manager that pointed out that the rear 3.25x10" opening was only to be used with the optional internal blower (i.e., the rectangular opening would not accommodate the required electrical connections, plus there would be a large rectangular opening in the top of the hood that would have to be sealed somehow).Did you try calling the blower manufacturer and talk to their tech department about your install? They may be able to tell you one way or the other. I was looking at different specs for duct sizes and that seems pretty straight forward. But then I also went to Broan's site and looked at some of their specs for different rated cfm units. Doesn't seem to jive.
http://www.waptac.org/data/files/we...duct system sizes and airflow quick chart.pdf
You could try what you mentioned above, if for some reason the necking down to 3.5 X 10 at the end of the run causes problems, maybe you could fit a larger size pipe through the sill. Maybe a larger rectangular size instead of larger round tube.
Mike Hawkins:smile:
I don't see the logic. Sure, moving air through a sharp 90 degree bend will restrict airflow. But I don't see how moving the blower location changes that. The bend is just as sharp, and if the blower is the same size, then it moves just as much air through that bend.I would avoid buying a fan blower for the hood, since that would just blow the air directly into the duct's initial 90-degree bend, creating a lot of back pressure.
Well, I agree the logic is a little elusive. As I visualize the installation of the hood with an integral fan blowing air directly into a vent that immediately turns downward, I see the air slamming into the back wall of the vent and being deflected back toward the hood with a lot of turbulence. Sure, some air will be forced down the vent, but a lot of static pressure will build up and the fan won't be efficient.I don't see the logic. Sure, moving air through a sharp 90 degree bend will restrict airflow. But I don't see how moving the blower location changes that. The bend is just as sharp, and if the blower is the same size, then it moves just as much air through that bend.
(However, it might be quieter with the blower in the basement)
I received the Broan fan by UPS from build.com, but had toi return it. The unit was bigger than I had visualized-- almost the size of a carry-on roller suitcase. The transitions ducts that came with it were also enormous-- they transitioned from the box inlets(maybe 6" x 18") to 10" round. I would have to further reduce it to 6" round to get the ducting through my sill... and there just wasn't enough room to do that transition.I'm not that familiar with the range hood venting, but I assume that 600 cfm means that is what the fan is capable of, but where the fan is. As you get further away from the fan, the cfm decreases. You need to find out what kind of cfm you would have at the hood if the fan itself was 10' away with bends and given duct size, and the loss after the fan. I have Whirlpool, about 230 cfm, and it works well enough. Smoke from the fried steaks is about 80% vented now - it does through about 6' of 5" duct that came with the house, but 5" is not adequate.
I found the Broan tech dept is not that well informed, I think more a handy guy who is reading off the charts. Given Broan's $200 range hood is not really engineered - just decoratively designed - I have low expectations from Broan.
Try Fantech. They make higher quality inline blowers and have charts about the cfm, duct size, and loss of cfm. It feels intuitively that the loss of cfm would apply to front as well. Their tech may be able to help you better.
Amazer98;292736 My contractor is trying to figure out if we can route ducting laterally across the tops of the cabinets and then turn through the wall said:That's exactly the way I did mine. I have a Broan Allure range hood. From the top of the unit I started with a short piece of 7" round, going into the short cabinet above. That goes into a 7" to 3 1/4" X 10" transition boot with a 3 1/4" X 10" 90 degree boot on top of that. I continued with 3 1/4" X 10" duct work across the top of the cabinets about 5' and then thought the outside wall with a termination cap on the outside with a spring loaded damper. I trimmed the 1" sides of the cabinets on top that stuck up to allow the duct to sit on the actual cabinet top. After the crown mold was installed, you can't see the duct. I have open cabinet tops due to a cathedral ceiling. Luckily the studs in the outside wall fell just right so going through was pretty easy. The hood works well and if I'm in the back yard on the deck in the good weather, I can smell what's cooking.
Mike Hawkins
