Get one that runs on a temperature sensor.
Best way to lower attic temperature.
Install electric ventilators and attic fans which remove hot air from an attic.
They have thermostats that turn the fan on at a recommended preset temperature of 100 110 degrees.
Also make sure your attic is ventilated.
In existing homes the question is important.
It will help to keep the attic much cooler in the summertime.
If you don t worrying about how best to keep the attic cool is a bandaid on a self inflicted wound.
Again i m assuming that you re not considering a sealed attic lowering the temperature of an attic that contains ducts can reduce your air conditioning costs.
When reroofing use white or pale gray shingles instead of dark ones.
Gable vents around 25 each plus 75 per vent for labor can lower attic temperatures about 10 degrees.
They are readily available and easy to install yourself.
Alternatively install passive vents such as gable soffit and ridge vents which are openings in the roof that allow hot air to escape.
Ideal attic temperatures shouldn t be more than 10 to 20 degrees hotter than outside temperatures.
Adding a radiant barrier to the underside of your attic structure will help reduce heat gain in the space but be sure to check your roof shingle warranty and make sure it would not be voided by such a measure.
A solar powered attic fan would be best.
A ridge and soffit ventilation system an extra 200 during reroofing will reduce attic temperature to around 100 degrees.
Use a thermostatically controlled roof mounted ventilator.