I have an unusual suggestion for ventilation. I have connected an intake vent hose (like a dryer vent hose) , from the outside of my house to the return plenum of my furnace. (I have a hot air system). When the blower is on, it sucks in some fresh air from outside through this intake vent. This air is cold in the winter and is fed directly into the furnace to be heated. This tends to pressurize the house a little and reduces the leaking of cold air throughout the house. When the furnace kicks on in the winter, you can definitely sense the fresh air entering. Yes it is a little cool at first until the furnace warms up. Also this fresh air continues to leak in through the intake even when the blower is not running and flows through the still warm furnace by natural convection. Even though I am introducing cold outside air into the system, I think it is not really hurting efficiency that much because it is displacing cold air that would have leaked into the house otherwise and I am controlling it to enter via the furnace. And the fresh air in the winter is definitely nice.
Mark