I have a couple quick (hopefully easy) venting questions and I'll provide more details as requested. 1) how does one go about connecting 3 1/4" x 10" ducting together? I want to make a short flange piece that feeds from the inside of the kitchen wall (behind the microhood) heading outside where it will mate with a standard aluminum 3 1/4" x 10" range hood damper. My hope is to allow the damper to slide snugly over the interior flange thus making it easy in the future to either re-side the house, replace the damper if damaged, etc. without having to pull the microwave down. Interestingly, the install instructions for exterior venting are VERY limited as written by the manufacturer. Also the "adaptor/damper" that is supplied with the unit is smaller than the 3 1/4" x 10" standard so there is no good fit between them at all. Very frustrating. I wanted to vent up, but no go. Straight out the back is the best way and is on an easy, exterior wall. Short run. With my flange plan I can then simply run some foam weatherstrip around the perimeter of the m-wave exhaust or the exterior vent flange to nicely seal the small space. I just don't know how to connect the ducting together since the all seem to butt against each other not sleeve inside one another.

Biggest issue (and the second question) is how to attach or vent through the wall with what's readily available.

You will be better served if you take the parts you are trying to put together and go to a local sheet metal shop. They will know exactly what you need and will probably have it in stock. This will save you a big headache.

As a side note you probably need S and drives to put it together but with out being there and seeing it I would not know for sure.

I would like to thank -you for your help answer's you have given us will help us thank-you again.I f I need help again I will ask .

HVAC1000 wrote: "As a side note you probably need S and drives to put it together"

What are "S and drives"?

Thanks for the good advice. I will find a sheet metal shop for help.

They are special fittings of the HVAC trade used to connect duct.