The retrofit and refurbishment (R&R) of existing buildings is increasingly regarded as a sustainable alternative to new construction, primarily due to its lower environmental impact. By preserving structural components such as concrete and steel, R&R significantly reduces material extraction, construction waste, and embodied carbon emissions. Furthermore, R&R projects present opportunities to enhance operational energy performance through upgrades in insulation, lighting, and the integration of active and passive design strategies, and thereby reduce operational carbon emissions. A notable hybrid (active and passive) strategy is the implementation of Earth-to-Air Heat Exchangers (EAHEs), commonly referred to as earth tubes. These subsurface systems pre-condition incoming air using the ground’s relatively stable thermal mass, thereby reducing mechanical cooling and heating demands. EAHEs are particularly suited to R&R contexts due to their low energy consumption, minimal maintenance requirements, and ease of integration with existing structures. EAHEs application supports improved indoor air quality, enhanced thermal comfort, and increased resilience to climate variability. This paper examines the performance of an EAHE system installed during the major R&R of an existing residential building in Canada. Despite a 40% increase in gross floor area, the project aimed to improve ventilation and passive cooling without raising overall energy consumption. Findings will assess the effectiveness of EAHE integration within the broader context of sustainable refurbishment and energy-efficient building design. The future application of retrofitting EAHEs to existing dwellings in Wales is currently underway and will also be discussed in an alternative climate zone.