We have a 10 YO range hood with dual fans that puts exhaust air from cooking directly outside. The outside opening is 10" wide by 3.25" tall and is rectangular. The duct work coming off the rear of the hood is also 10" by 3.25 " and rectangular shaped. The hood came with this ductwork as an install kit. The exhaust fans work great. This hood system came in a dual configuration which would permit either exhausting air vertically or horizontally out the back depending on which way the deflector was positioned. Anyway, we go straight out the back to a small rain hood that protrudes from the siding. This aluminum rain hood deflects downward and shields a gravity operated axial butterfly flap that supposedly closes off and prevents cold air from coming in. It doesn't. It's so lightweight and flimsy that even a mild puff of air causes it to swing open. I've tried even weighting the butterfly with a couple of quarters to get it to remain closed but to no avail. We decided to just not use the hood in winter and block up the opening to save on heat. This vent is on the north side of the house; the coldest part of the property.
I am looking for something else to install and am interested in some ideas from the experts here. The guys at Lowe's and Home Depot haven't a clue. In fact neither store could recommend from stock an item that addresses this problem.
Appreciate any advice given. Thanks, all!