It should be set between 38 and 40 . If the food feels icy, the temperature is too low. Whenever someone opens an oven door to check progress, the oven loses 25 to 50 of its heat. More gas or electricity is needed to reheat the oven, wasting more energy and money. Microwave ovens are more energy efficient for heating small items such as a bowl of oatmeal or a plate of leftovers.
Toaster ovens work for smaller items as well.
Use the smallest pot for the job. And put a lid on it. Choose a burner that matches the size of the pot. If the burner is too big, much of the heat is wasted. If it's too small, the food won't be heated evenly.