Need Winter Ducting Help

Ok guys i need some wisdom. Well the problem is i am trying to figure out a way using some kind of y and or flange to bring the exhaust back into the room once a certain temp is reached. i know i am gonna need a thermostat, idk what kind to buy that turns on once it gets so low but i might need one that turns off when it gets so high because of the normally open or closed flange. i have looked for y spilters that have a flange in it but no success i am guessing from research ima have to use a flange and a normal y but that way i still will have some air going outside so im confused thats why im asking the pros sorry

i will not use a heater lol when my lights make plenty heat these dam cooltubes work too good

forgive me if this is a repeat question

Why not do a long run to a filter say 7 feet, then the air cools by the time it is filtered.
MD.