Most energy companies recommend scheduling a professional pre-season service and maintenance bi-annually. The best time to slate these is before winter and again before summer, ensuring proper functioning prior to entering the two seasons of greatest HVAC demand. Ductwork cleaning is invasive and time-consuming, though it is necessary every three to five years. The most cost-effective way to keep an HVAC system clean is coil cleaning and cleaning air handling units as recommended by the National Air Duct Cleaners Association and the manufacturer of the unit. Regular maintenance of your HVAC unit ensures maximum efficiency and prevents considerable expense resulting from neglected systems.