Abstract: Disclosed is a power ventilator attached to a roof for ventilating an attic or the like. The power ventilator is provided with a base which attaches to the roof adjacent an opening in the roof. The base has a hollow cylindrical housing which forms an air duct. A plurality of wire supports are used to attach a generally dome-shaped cover and an electrically powered fan and motor to the cylindrical flange. Each wire support has a curved portion which conforms with and contacts an arcuate portion of the cover. Each wire bracket has a flange which extends into the interior of the cylindrical flanged portion to support the fan motor. A screen is attached across the opening between the cover and the cylindrical flanged portion. A thermostat means is connected to the exhaust fan to operate the fan when the temperature in the attic exceeds a first predetermined temperature and disengages the fan when the temperature falls below a second predetermined temperature.