Calling all energy efficiency pros!

New poster here ... with a ductwork question. In our kitchen reno we are installing an island hood. It uses a 6" round duct. The only workable way to run the ductwork is to transition to 3-1/4 x 10 and go across the ceiling to the nearest exterior wall. There is an open bay and the joists run the way they need to in order to do this. Here are the issues: (1) To get into the bay I need a slight -- maybe 3" -- offset from where the duct comes up in the back of the 10" x 10" hood column. I'm pretty sure there is room to do the offset then go to a 90 degree 6" round to 3-1/4 x 10 transition. What I'm not sure of is the right piece to do this. HVAC supply house suggested a short piece of flex duct but the manufacturer says "Always use rigid type metal ducts only. Flexible ducts could reduce airflow by up to 50%." Can this be done with one of the 6" adjustable elbows, like this one? [url]https://images.homedepot-static.com/productImages/fb1e4388-401a-4895-ac69-78db618d88f2/svn/elbows-b90e6-64_1000.jpg[/url] (2) At the outside wall the bay I am in comes out under a steep eave (slope probably close to 12/12). It will be a significant challenge to install the backdraft damper (looks like [url]https://images.homedepot-static.com/productImages/73698e05-8184-4c36-939f-9d4755951ba9/svn/broan-grow-room-ventilation-649-64_1000.jpg[/url]), but it may be doable if I cut the hole in the trim large enough to insert the damper at an angle. It will also be a challenge to mount it with screws since I can't really get the tools up under the eave, and also the larger hole will reduce the area the flange covers. I can imagine going up through the roof but that would also be a major challenge since the attic area under that steep section of roof is totally closed off and inaccessible. Ideas on addressing either of these issues would be very helpful, thanks! Tom

The wife and I bought a new washer and dryer. Today the delivery guys came and refused to hook up the dryer because they said I didn't have metal ducting to hook it up to. The house was built in 1989 and still has the original white plastic dryer hose. Problem is the hose is built into a finished wall and above a finished ceiling. I can see part of the hose as it passes through a utility room on the side of the house and goes outside. Is there any chance I can pull a replacement hose through with the old plastic hose? Do I have any other options?