A vehicle exhaust system includes an outer housing defining an internal cavity surrounding an axis, an inlet baffle configured to direct engine exhaust gas into the internal cavity, an injector that is configured to spray a fluid into the internal cavity to mix with engine exhaust gas, and an inner wall spaced radially inward of an inner surface of the outer housing to define a gap. The inner wall has an impingement side facing the axis and a non-impingement side facing the gap. At least one heating element is associated with the non-impingement side to actively heat the inner wall to reduce spray deposit formation on the impingement side.