with vegetable oil in the heat exchanger
It's not the size of the heat exchanger but the temperature that you wanted to raise it by which is the important feature, and the answer would then be so many barrels of vegetable oil. To raise the temperature of 1 litre of water by 1 degree you need 1 kcal, so we are talking 750000 kcal to raise your water temperature by 10 degrees. A gram of carbohydrate delivers 4 kcal (nutritional science applied to physics). Burning it is not going to be terribly efficient, but the numbers suggest you are going to need to burn something like 190 litres of oil. If I have misunderstood you and you want to circulate vegetable oil which you have heated electrically, the 750000 kcal converts to about 870 kWh of electricity.
