The international standard, ISO/IEC 17025 was developed to determine technical competenceand to evaluate laboratories throughout the world. Accreditation bodies playing a vitalrole are increasingly using proficiency testing methodology as a tool to ensure thecredibility of their accreditation programs. The successful completion of a well-designedproficiency test can validate the measurement method and uncertainty budgets of a testinglaboratory. Additionally, proficiency tests can provide a good indication about thequality of the test results. An important part of inter-laboratory comparisons andproficiency testing is the determination of the associated error analyses which arefocused on uncertainty values. This paper presents the implementation of proficiency testsusing inter-laboratory methodology among five different acoustic laboratories. These testswere carried out on 5.27 KWCooling standard unitary air conditioner, A/C, suchas through-wall or split room standard A/C units, for the assessment of Housing &Building National Centre acoustic laboratory. Analyses of results show a good agreementfor En-Value among the selected laboratorieswhen compared with the lowest uncertainty as stated by proficiency tests standards.