This presentation summarizes the results of a four year study on quality installation issues: the effect of installation errors (e.g., leaky duct, improper refrigerant charge, oversized equipment, incorrect air flow, etc.) on the performance of residential unitary equipment; the extent that operational deviations are significant; whether the deviations (when combined) have an additive effect on equipment efficiency; and whether some deviations are affected by geographical/climatic differences. With an understanding of this information, field personnel are better positioned to focus attention, resources, and remediation effort on the varied design, installation, and maintenance practices in the HVAC sector.