The likelihood of additional disease outbreaks in the future highlights the need for effective strategies to reduce airborne disease transmission. In-room germicidal ultraviolet (GUV) systems are increasingly recognised as an effective intervention for reducing the spread of infectious diseases in indoor environments. Large-scale chamber testing plays a critical role in validating the performance of these systems under controlled conditions while remaining representative of real-world environments. However, at present, no unified standard exists for conducting such tests or for translating experimental results to real-world applications. This review summaries existing standards for large-scale testing of in-room GUV systems and proposes best practices for experimental design, measurement, and data interpretation. Current protocols are evaluated with respect to chamber dimensions, environmental control, air mixing, ventilation, and safety considerations. We also summaries commonly used microbial and non-microbial challenge agents, as well as aerosol generation and sampling methods. The strengths and limitations of steady-state, static decay, and dynamic decay testing approaches are compared. Key knowledge gaps are identified, notably the lack of standardised methods for quantifying UV inactivation kinetics of aerosolised microorganisms. The findings provide a framework to support more consistent evaluation, comparison, and design of GUV systems to improve indoor air quality and infection control.