Aims: We consider viscous and resistive energy dissipation in the flaring solar corona. Methods: We compute energy dissipation rates, associated with magnetic merging in three dimensions. We examine an exact 3D solution for steady magnetic merging in a viscous resistive incompressible plasma. We use the Braginskii stress tensor to model viscous effects and derive scalings for the resistive and viscous dissipation rates. We evaluate the dissipation rates for typical parameters of solar active regions. Results: Large-scale advective flows required to sustain resistive current sheets are shown to be associated with significant viscous losses.