If you are constantly having to contact an HVAC professional for constant repairs then it might be time to replace your HVAC installation. It might be that your heating equipment is approaching the end of its lifespan especially if it is over thirteen years. No matter the number of times you have air duct cleaning if it is the heating and cooling equipment that has a problem it will not be of much help. Duct cleaning only cleans the HVAC duct and the other conduits but will not do much for equipment if it is beyond repair. Last week I visited the dentist and came across the HVAC provider truck in the parking lot. The HVAC tech had come to replace the existing system with a new HVAC zone control system. They had also invested in air quality systems. They have an air purification system which at first I thought was an air purifier but it turns out it was an air scrubber. This would explain the high indoor air quality in the clinic. The temperature control of the old system was more on the cool side but it was never uncomfortable. On the two occasions I had brought her here, my niece complained that it was too cold but I attributed it to nerves since the indoor environment never bothered me and I had been there several times. I also noticed that it was the same homeowner solutions company that had done my heat pump repair last month. Their repairmen were very professional and very good at their work. I do not know of a single person that sought their services and had complaints about their work.