The AquaHot on our '97
Dynasty works exactly as MrMark described it. On cold mornings I can run the diesel boiler on the AquaHot, hit the dash switch and the coolant will circulate through the Cummins to preheat the engine. I am not mechanically knowledgeable enough to explain how it works, or if it is the coolant or hot water, but I can tell you that it does. Perhaps not all coach builders provided this function, but it is included as an option in the owners manual which came with our coach way back in 1997.