You can use the rower outside in dry weather conditions. The Concept 2 indoor rower is a solid construction with a powder coated frame structure, a stainless steel seat track and a nickel-plated chain. The PM5 performance monitor has delicate electronics and should be protected against water / high humidity.
Storage of the rower should is done best inside in dry conditions. You can buy a cover for extra protection against dust and dirt. The cover is not designed to provide full weather or heat protection.