What is the term for mechanical systems that were installed before the adoption of specific codes?

The term for mechanical systems installed before the adoption of specific codes is "Legacy Systems." This term is commonly used to refer to older systems, which may not conform to current standards or codes but are still in operation. Legacy systems can include a variety of mechanical, electrical, and plumbing installations that were put in place prior to changes in regulations and requirements.

While "Existing Mechanical Systems" might sound plausible, this term typically references all systems that are currently in place, regardless of when they were installed. This broader classification does not specifically highlight the historical context regarding building codes.

Similarly, "Pre-Code Systems" and "Historical Systems" might imply older systems, but these terms are not as widely accepted or used as "Legacy Systems." "Pre-Code Systems" suggests a focus solely on the absence of specific codes at the time of installation, whereas "Historical Systems" may imply a significance related to their age or cultural value rather than their compliance with building standards.

In summary, "Legacy Systems" is the most accurate term, as it encompasses the idea of systems that exist due to regulations that were in effect at the time of their installation, reflecting a direct relationship with the progression of building codes.