Cold Air Return vent?
There are several big return vent throughout the house. The one I am describing is on the ductwork where the return meet the furnace.
Answers: Generally you should close that vent in the summer and break open it in the winter. In the winter it will sustain pull the cooler nouns out of the basement, to be heated. This help even out the temp from the basement to the rest of the house. Most flow thru humidifiers require single a 6' diameter hole to tie them in. You can pretty much cut it within anywhere on the return and it'll work just fine. Remember to install a damper surrounded by the bypass (6") and close it in the summer. Hope this help.
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