I have received two quotes from two installers for a new furnace and A/C unit. Our existing unit is 18 years old. One installer will install a new line set. The other installer will use the existing line set. What do you recommend? We also have a two zone damper system, 18 years old. It still works fine. Both installers recommend to replace the damper system. Should I replace the damper system with a new one? Our old furnace is 80,000 btu gas furnace and A/C is 2.5 ton Lennox. Do you recommend an air cleaner (Aprilaire Air cleaner #2410)?