Which guideline is essential for installing a new boiler?

Ensuring proper venting is crucial when installing a new boiler because it directly impacts the safety and efficiency of the heating system. Proper venting allows for the safe expulsion of combustion gases produced during the boiler's operation, which includes potentially harmful substances like carbon monoxide. It also ensures that there is adequate air supply for combustion to occur, preventing issues such as backdrafts or incomplete combustion. The correct venting system must adhere to both manufacturer specifications and local code requirements, reflecting a balance between safety standards and operational efficiency.

The other options present practices that could lead to various complications. Ignoring local building codes can result in legal repercussions and safety hazards, while employing any available installation method could undermine the integrity of the system. Additionally, skipping manufacturer’s instructions may lead to improper installation, reducing the unit's efficiency and possibly voiding any warranties or guarantees. Proper venting, therefore, stands out as a fundamental aspect that must not be overlooked in boiler installation.