Evaluating ventilation effectiveness and contaminant removal efficiency is crucial for indoor air quality and occupant well-being. This study introduces a novel approach to measuring ventilation effectiveness by utilizing small, portable thermal dummies equipped with a fan and heating element, which replicate human heat output and airflow patterns. These dummies are smaller than conventional cylinder thermal dummies and aim to provide a more accurate simulation of human heat convective airflows compared to tested alternatives, including portable fans and cylinder thermal dummies. Both the concentration decay and constant concentration methods are employed, with measurements taken at multiple points in the room and in the extract duct. CO2 is used as a tracer gas to assess air change effectiveness and contaminant removal efficiency. The newly developed dummies are compared with humans, larger dummies, and portable fans to evaluate their suitability for room airflow assessments. Initial findings suggest that portable fans exhibit significant differences in velocity fields compared to dummies and humans, making them unsuitable for ventilation studies. New, smaller dummies designed to replicate human convective airflows have proven promising in on-field measurements and offer accurate alternatives for evaluating air distribution systems. Measurements were conducted to validate these small thermal dummies as substitutes for humans and larger dummies in ventilation studies. This could potentially lead to more efficient and accessible methods for assessing indoor air quality. The findings could have significant implications for designing and testing air distribution systems, particularly in scenarios where human subjects or complex thermal manikins are impractical.