The most common form of ventilation is natural, because it requires nothing except hot air. Heat rises and, when it does, it pushes out at ventilation points to circulate in cold air. This is known as the stack effect and it works well for most homes.

However, in some cases natural ventilation isn’t a feasible option for air flow and will require help to get hot air out. When that happens, power is given to a mechanical method of circulation.

While every home can’t use mechanical ventilation due to local codes, home construction, and the weather, 2 things are certain: The hot air leaving your home is referred to as exhaust and the cool air that replaces it is the intake.

Each needs a special vent to work properly, with exhaust going out of ridge vents as a frequent option. If you’ve had your roof worked on, you might have heard the term “ridge,” which is the apex of 2 points on your roof.

Ridge vents are installed at those points to avoid standing out, but they provide locations for the hot air to leave your attic and upstairs. Non-mechanical vents are roof and gable louvers, but there are also wind turbines and power ventilators that can go on the outside for exhaust.

The turbines need a strong source of wind to work, though, and power ventilators need power. The latter is used in low-plane areas without much wind while the former can be seen in higher areas, like the mountains.

One of the most-common questions homeowners ask is how many vents they need. There’s no definitive answer, but you need one for every 300 square footage of roof if you have a vapor barrier in place. Without one, you might want one every 150.