My master bathroom did not previously have bathroom fan, but I installed one and have had wonderful results with keeping the steam from building up and exhausting the moist air. I am using both a fan and a roof vent that have pretty weak metal flaps to reduce the cold air from making its way into the house. I can hear the flap on the roof vent at times during very windy conditions, but not often.
I have taken showers without turning the fan on and the warm, moist air finds its way out of the vent very easily. It is amazing how much just having the air path in place helps the exhausting compared to when a fan was not present. This does concern me though, as I wonder, if air can leave the bathroom that easily with the fan off, could I be losing heated air when the fan isn't turned on? I plan on insulating the pipe that is in the attic now, though I am not sure if this would affect the rising of the warm air/dropping of the cold air.
Any thought or opinions? Do I need to be concerned about this?