Our hypothesis states that it is possible to reach a suitable indoor microclimate quality in existing vernacular mountain-dwelling houses by compliance with the appropriate regime for using the building. The case study buildings are preserved vernacular mountain dwelling houses constructed before 1945 in the Kraslice microregion of the Sudetenland in the Ore Mountains in Czechia. These buildings are mostly made of log construction, brickwork, or timber-framed construction. They have a unique regional typology, which has adapted to the harsh winter conditions throughout history. The preserved vernacular architecture in this region has artistically valuable architectural expression, containing unique contextual elements of Heimatstil, which are desirable to maintain. Therefore, the building modifications of the exterior of these buildings are undesirable from an architectural point of view. We emphasize an optimized use regime rather than building modifications. We chose one preserved vernacular building as the case study house and conducted a field monitoring of its indoor microclimate. The results indicate that the indoor microclimate meets satisfactory standards. We analyzed key elements of the use regime to obtain data that can serve as best practice. These findings will be used to recommend an optimal use regime for improving the interior microclimate in future case studies.