Natural attic ventilation and sealing also keeps attic cold in winter by blocking the entry of heat and moist air from below. In summer, natural air flow in a well vented attic moves super heated air out of the attic there by protecting roof shingles and removing moisture.
Ideally, half the vents should be located in the soffit at the bottom of the roof and half in the gable or ridge vents near the top to allow for natural circulation of air through the attic. Example: a 50’ X 30’ attic would have a total area 1,500 sq ft, divided by 150 equal 10 sq of total vent space.
The combination of a ridge vent along with continuous soffit vents gives you a flow through of air similar to how a chimney works.