DEAR TIM: My home has two of the spinning turbine vents. I have been told by several people that it is a good idea to stuff insulation in these during the winter months so that warm air is not sucked out of my attic space. Is this good advice? Are these turbine vents really effective? I don't see many of them on my neighbors' roofs so I wonder if I should remove them. Kevin M., Canal Winchester, OH

DEAR KEVIN: Don't touch those vents! They are splendid ventilation devices. In fact, I installed these same vents over 25 years ago on the second home I owned. They were hardworking devices that Mother Nature paid to operate. In fact, the same vents are still in place on the home and each time the slightest breeze blows, they do a great job of pulling air from the attic space.

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.

It is best to check attic temperatures at night after the sun has gone down.  If your attic is well insulated, the actual temperature of the air inside your attic should be very close to the actual outdoor temperature.

However, it is possible for turbine vents to pull conditioned air from the inside of your home. Modern building principals and most model building codes mandate that you have soffit ventilation vents that act as intake air locations. As air is pulled from the attic space by the turbine vent, ridge vent or even an electric powered fan, the same amount of air must be allowed to flow into the attic space where the roof passes over the exterior walls of the home. If there is not enough soffit air coming in, then the vents may create a partial vacuum in the attic space. To relieve this pressure, the vacuum may pull air from the inside of your home. This is not a good idea.

If you decide to add more turbine vents to your roof, be sure to buy ones that are aluminum. These will not rust. In addition, pay attention to the maximum roof pitch that will work with the turbines. The turbines are adjustable so that the spinning part is level even though the roof is slanted. Not all turbines will fit all roof pitches. The maximum roof pitch is almost always printed on the box label. Finally, be sure the ball bearings are permanently lubricated and sealed. Nothing is more bothersome in the middle of a windy night than a squeaky roof turbine!