Do I have to buy both indoor and outdoor units when I replace my heat pump?

Yes. Champion AC policy on this is we will not bid an installation without also bidding a matched indoor unit. Heat Pump systems are bought by a seer, cooling rating and a H.S.P.F. (heating) rating. The only way to get the ratings that you paid for is with a matched indoor unit. Not changing the indoor unit can also cause problems with defrost cycles, reversing freon pressures, and void factory warranties with equipment manufacturers.