upstairs for air flow.? This vent used to be used in many older homes. it is basically a hole cut in the 2nd story floor through to the ceiling of the downstairs that allows air from downstairs to flow upstairs,. we have a woodstove downstairs and would like to get more heat upstairs. this vent is basically 2 grates, one upstairs on the floor and one below it in the downstairs ceiling. there are no fans involved just gravity fed?