HVAC systems should be designed to meet the needs of a specific building based on its design, use, and occupant activities. The HVAC system should filter the air, heat or cool as necessary, and control relative humidity during the cooling season. Some systems also introduce outdoor air to dilute building contaminants. Then, the tempered air is circulated throughout the structure. A poorly maintained HVAC system can allow water to build up in the unit, creating conditions where the system itself can become a reservoir for biological contaminants. Inadequate systems can also allow high moisture levels that foster the growth of mold and mildew. For these reasons, it is very important that HVAC systems be inspected on a regular basis to ensure that the systems are clean and functioning as designed. It is also recommended that an air quality test for mold be conducted if you suspect an issue.