I am doing a kitchen remodel. I have gutted the kitchen down to the studs. I have complete all electrical, and need to run duct work for a range hood. The House never had one. I am looking at two diff over the range microwave/hood units one has 6" round, then other has 3 1/2 x 10. I know there are transitions to convert from one to the other. Not knowing which one I will end up with. What do you recommend for the wall cap. ( the duct will come in through the top of the cabinet above the micro. then run over head through the joists, and out the joist header. I will need to cut the whole in the joist header. So should I cut a 6" round or 3.2 x 10 rectangle? I will probably use 6" round in the ceiling do to a tight space in one part of the run. Thanks

I have a 1925 house, about 1100 square feet, into which a new hi-efficiency side-venting furnace was installed, in September. We are doing some major work on the interior of the house prior to moving in. My question is about the quantity of cold air return needed. There are currently three approximately 1.5 ft by 3 ft. (I am not in the house now and havent measured them exactly) cold air returns. I would like to get rid of one of them. Is there any reason to think that would be a problem? thanks in advance.