I have 25 yr old SEER 10 GE heat pump. Heat exchanger is in excellent condition. If I go to R410 I need to replace lines and both units. If I stay R22 I can do only condenser. If I go to SEER 16 do I get any benefit or do I just do the SEER 13. As I get it, either way I only need to replace condenser unit and recharge - no valve or line or other replacements are required although I will have less efficiency than all new system.