In effectiveness NTU method for heat exchangers, we have effectiveness of the heat exchanger defined as
$$\epsilon = \frac{Q_{actual}}{Q_{max}}$$
Where $$Q_{max} $$ is the maximum rate of heat transfer in a counter flow heat exchanger with some prescribed inlet temperature and heat capacity rates.
$$\text{when}\begin{cases} C_H< C_C, & \dot{Q}_{max} = C_H(T_{h,i}- T_{c,i})\\ C_C< C_H, & \dot{Q}_{max} = C_C(T_{h,i}- T_{c,i})\\ \end{cases} $$
What will be the maximum rate of heat transfer that will be taken when heat exchanger is balanced i.e. $$C_h = C_c $$