Which type of valve is required for bottom-fed water heaters?

For bottom-fed water heaters, a vacuum relief valve is essential because it allows air to enter the system to prevent a vacuum from forming. When hot water is drawn from a bottom-fed water heater, especially if multiple draw points are being used simultaneously, a vacuum can occur as the water is extracted. This can lead to complications, such as collapsing the tank or siphoning back contaminants into the system.

The vacuum relief valve acts as a safety device that opens to allow air into the tank when the pressure inside drops below atmospheric pressure, thus preventing the formation of a vacuum. It plays a crucial role in maintaining the integrity of the system and ensuring safe operation.

In contrast, other types of valves serve different functions. A pressure relief valve protects the system from excess pressure; a temperature relief valve is designed to mitigate excessive temperatures; and a mixing valve regulates water temperature for safety and comfort but does not address the vacuum issues inherent in bottom-fed water heaters.