I plumbed a very efficient 250 litre calorifier tank, accumulator tank and expansion tank into the vans radiator system drawing off only the hot water from the engine using the calorifier tank as a radiator means to store the heat and ran water for the window cleaning pump through the heat of the calorifier tank very successfully. I fitted a bypass so I could stop drawing water from the engine when it was hot enough as I could get the water up to hundred degrees if not careful. Fitted a thermostat to control the temperature. It is not easy to fit and set up, but once done it was a very efficient system provided the wfp tank and all hoses including radiator hoses were efficiently insulated. Had to make sure to use copper tubing of half metre for pressure release safety blow out valve as a safety measure. Used it for three years very successfully. Only reason I took it out was I sold the vehicle and never got around to fitting it in new vehicle. In principal it works brilliantly providing you are only trying to heat the water that passes through the calorifier tank and not the whole wfp tank which is where people go wrong.