For small buildings, this is usually ductwork. Rectangular lines represent supply ducts (blowing air). Circles with "R" represent return ducts. You are looking for:
Understanding how to read and interpret these drawings is essential for homeowners, developers, and DIYers alike. It ensures that everyone—from the architect to the electrician—is on the same page, literally. 1. What Are Construction Drawings? Understanding Construction Drawings For Housing And Small