Depends how you look at it, the Carnot engine is in principle reversible. You can either let heat move from hot to cold and get work as an output at efficiency

Depends how you look at it, the Carnot engine is in principle reversible. You can either let heat move from hot to cold and get work as an output at efficiency (T_hot - T_cold)/T_hot, or input work and move heat from cold to hot at efficiency T_hot/(T_hot - T_cold).