Wow what an AWESOME ship and fantastic crew. We sailed with 6,489 people and with the exception of the on-board embarkation and trying to contact Guest Services, the ship never felt crowded. However the Harmony of the Seas has a very serious flaw in the HVAC (ventilation) system that must be addressed. For some unknown reason even though smoking is NOT permitted in the Boardwalk neighborhood (kids area), in the Fitness Center, and on the running track by the Fitness Center, those areas had so much cigarette smoke that they were unusable by anyone with Asthma or any breathing difficulties. The smoke was reported to the Front Desk and Spa manager who confirmed it but they said that "engineering was notified and there was nothing that they could do". This situation was totally UNACCEPTABLE. This is a very kid friendly ship, but we could not allow our kids in the Boardwalk neighborhood (from the Carousel to kids rock wall area) and we could not use the great Fitness Center and track.