A symmetry-adapted filter-diagonalization method is used to calculate the vibrational spectrum of planar acetylene. In this method, vibrational eigenvalues in a given symmetry are obtained by solving a generalized eigenproblem in which the Hamiltonian and overlap matrices are assembled from symmetry-adapted correlation functions. Since no filtered state is explicitly needed, the calculation requires a relatively small memory. The numerical efficiency is further improved as the correlation functions belonging to various symmetry species are generated from a single wave packet. Comparison with existing data for the acetylene system confirms its accuracy and efficiency.