Abstract: A work vehicle comprises an internal combustion engine and a catalytic converter coupled to the exhaust of the engine. A reduction agent system provides for injection of a reduction agent, such as urea, upstream of the catalytic converter. Coolant heated by the engine is directed to the reduction agent system to defrost/heat the reduction agent, and is also directed to a vehicle cabin heating system. Flow of coolant may be preferentially directed to the cabin heating system rather than to the reduction agent system, such as following vehicle startup, particularly during cold-weather operation. Flow may be altered to favor the reduction agent system, such as based upon time and/or the temperature of the cabin.