The boiler vents are installed:

The boiler vents are installed at the highest part of the steam side to ensure that any accumulated air or non-condensable gases can be effectively expelled from the system. This is critical for maintaining efficient boiler operation and preventing issues like reduced heat transfer, which can occur if air pockets remain in the system.

By locating the vents at the highest point, it allows for the natural rising of these gases to the vent outlet, facilitating a more efficient purging process. This placement is essential in ensuring that the boiler operates at optimal pressure and performance levels, thereby supporting overall boiler safety and efficiency.

Other potential locations, such as the header or the superheater inlets, may not effectively remove all air or gases due to their relative positions within the system. The steam side of the mud drum is also not ideal for venting because it is important for other operational functions within the boiler. Therefore, positioning vents at the highest part of the steam side is the most effective approach.