What defines a 'vented' system in hot water plumbing?

A 'vented' system in hot water plumbing is characterized by its ability to allow air to enter the tank as the water is drawn from it. This feature is essential for maintaining proper pressure and ensuring that the system operates effectively. In vented systems, the tank is open to the atmosphere at certain points, which helps prevent a vacuum from forming as water is drawn out. When water is used, air fills the space coming from the vent, allowing the tank to maintain its performance without creating negative pressure that could hinder water flow.

In contrast, a sealed system does not allow for air exchange, which can lead to pressure buildup or potential failure of the system. While pressure is an important aspect of hot water systems, vented systems operate under gravitational pressure rather than being constantly pressurized. A complex pump system is not a defining feature of a vented system, as such systems can be simple and do not necessarily require pumps for water movement due to their design, which relies on gravity and atmospheric pressure.