For pasteurizer of 1000L/hour you need 1500 liters of hot water of 80-85 degrees. The hot water goes in the pasteurizer at 80-85 degrees and will come (return water temperature) out of the pasteurizer with about 65 degrees. Your heating solution (making of hot water by steam, wood, gas or electric) has to warm up this return temperature to 80-85 degrees. Than it goes back to the pasteurizer. Above mentioned has to be calculated in line with the wished temperatures of the customer.