We performed a 3 heating maintenances on 2015 gas systems. We checked amps, filters, electrical, gas valves, cleanliness, flame sensors, igniters, and safeties. We noticed some potential issues in all 3 systems. All 3 blowers wheels have some build up present. This hard strain to the motors and control modules. 2 of the outdoor units have heavy build up on the coil. This leads to strain on all electrical aspects of the outdoor units. The air quality check showed high particles and chemicals. We noticed a duct with a kink in it potentially causes poor air flow. The units are not currently protected from surges. We presented options to address these noticed potential issues. The customer declined all options at the time of service, and we emailed them out to the customer.