Circular soffit vents are used to draw in cooler air at the eaves, which is then heated by natural convection in the attic and exits through vents in the roof or the gable ends or both. Older houses rarely have soffit ventilation of any kind, which can lead to problems. Circular soffit vents come in different diameters and are easy to install using a hole saw. They are available in plastic or aluminum, and come in white or brown plastic or aluminum, and mill finish (unpainted) aluminum. The advantage of using mill finish aluminum is that it can be painted if white or brown doesn’t match the color of your overhangs so that it blends in.
You need one square foot of ventilation for each 150 square feet of attic floor space. Divide the total by two; you will need half at the soffit and half at the top of the roof. To calculate the square footage of circular soffit vents, use the net free area which is listed in the manufacturer’s specifications. Before installation, check in the attic to make sure insulation isn’t packed at the eave, which will block air flow. It is a good idea to use stainless steel screws in the installation as they won’t rust.