Came out because the customer was concerned about his Hvac system not heating properly. The system is working but not efficiently. I set the blower motor to its highest speed. I checked static and gas pressures and they were good. I removed the filter from the system because it was restricted. I checked my delta T and the temperature at the register and they were in the low 80’s. I checked the out door unit because this system is a dual fuel system. The fan was spinning and the suction line was hot. Both the outdoor and indoor unit were running at the same time therefore the house should have gotten better temperatures at the registers. I ran the system for 45 minutes straight and the temperature stayed at 71 degrees the entire time. Recommendations: The furnace is 20 years old so it will not operate at its optimal capacity anymore. The system needs to be replaced.