Hello All,

Currently have a 5ton 10seer heat pump (r22). Need to replace the failed indoor unit.

I got a new 13seer R410a indoor unit (model # gb5bm-060k-c). Will this work with the old 10seer R22 condenser outside? Are new lines required?
I know there has to be some efficiency loss, but what else should I know about this?

No, you need a new outside unit or to find an r22 inside unit. If you must proceed with the indoor unit, have a good service technician replace the metering device.