I'm just 2 to 3 weeks from taking my van up to SMB Indiana for build out. I'm strongly considering the Flat Plate water heater. I understand that the engine has to be idling to circulate the hot coolant through the flat plate. I was just wondering how long it would take for the coolant to warm up enough to have hot water after cold start? Diesels run very cool when idling and I am concerned I would have to wait 30 to 45 minutes for the engine to heat up enough. I believe the Ford diesels have a high idle setting but to my knowledge my GMC van doesn't have anything like this.
I have the flat plate hot water heater in a Sprinter. I assume the GMC would work the same. I get hot water in about 5+/- minutes. I recommend that you have SMB install a hot water tempering valve at the same time with the flat plate exchanger. Without one the water can get very hot and give you a nasty scald if you are not careful.