
Originally Posted by
http://www.askthebuilder.com/roof-turbine-vents/
The last thing you want to do is stuff insulation in the vents. Ventilating attic spaces in winter months is often more important than venting them in summer. Water vapor from the inside of a home can drift up and into an attic space. If this water vapor is not quickly exhausted to the exterior atmosphere, it can often condense upon the cold roof framing members and the underside of the roof sheathing. It can get so bad that water can drip from the underside of the roof and when the temperature gets low enough, frost can actually form up inside the attic. Moisture conditions such as this can lead to wood rot and mold growth.
Depending upon the diameter of the vents and the wind speed outdoors, the turbines can expel vast quantities of humid air before it becomes a problem. A small 12-inch diameter turbine vent with a constant wind speed of 5 miles per hour (mph) can remove 347 cubic feet of air per minute (cfm) from the attic space. A single 14 inch diameter turbine vent that is subjected to 15 mph winds can expel up to 1,342 cfm of air! If the winds are still, the vents still allow air to drift up and out of the attic space, although not nearly as much.
It is also a myth that turbine vents remove warm air from attic spaces in winter months. If the air temperature in your attic space is very warm while it is cold outdoors, I maintain that you might have inadequate insulation and/or you are up in your attic on a bright sunny day where the radiant energy of the sun is heating the attic space.