When an HVAC system works, building occupants don't even know it's there no news is good news. The bad news is, in a recent survey done by the International Facility Management Association, too cold and too hot ranked first and second of top 10 office complaints. Hot and cold problems can be caused by many factors: too little capacity, too much capacity, lack of zoning, too little control, varying space usage, varying solar load, changes in occupancy, changes to the space envelope, drafts and diffuser performance, or too little ventilation.