I agree with DankHobbyist. If you are pulling cold air from outside then you will ffind it easiest to control the grow atmosphere by having a room within a room. Then pull the outside air into the outer room and heat it there so that it is at a suitable temp before going into the grow space. You will find in the winter, the cold and damp outside air, when it comes into the warmer room and is warmed itself to the 70s that the dampness in the air will diminish as the air warms, and the RH will drop a good bit depending on how damp the air is and how warm the room air is. I like to place a heat source next to my intake air for the room so that it can be warmed as it comes in. It takes some trial and error to set this up to be just right, and as the temps swing throughout the season, you will have to continually have to make adjustments to account for the changes but it gets easier after you have dialed it in.