How to cook with the most efficiency

Q: I cook a lot at home, usually just for my husband and myself now that the kids are older. Is it more efficient to use smaller countertop appliances instead of the range and oven?

A: Cooking efficiency is a function of how much gas or electricity is used, and how much of the heat ends up in the food you are cooking. Most excess heat is lost into the kitchen and exhausted by the range hood.

Using smaller countertop cooking appliances can save energy, but sometimes using the range or large oven is a better option. This depends on the season (heating or cooling), the quantity of food being prepared and the types of food.

The most energy savings can be realized in summer. Any excess heat lost from range burners or elements heats the room air, making the air conditioner run longer to remove the excess heat and humidity, so it is a double energy loss.

In winter, the excess heat from cooking helps heat the house somewhat. With the house closed up, people tend to run the range hood more, so much of the heat is lost outdoors. Also, heat produced from an electric range is only about one-third as efficient as from a heat pump.

When using your range, it’s important to match the pot size to the burner or element. If the pot is too large, foods don’t heat evenly. If the pot is too small, heat comes up around the sides, not through the bottom, and is lost to the room. Using a pressure cooker can reduce cooking times.

When cooking a small quantity or just one dish, a small appliance, such as a toaster oven, is often the best choice. It preheats faster, and the heating element wattage is much lower than the range oven.

The thermal mass of the small oven is low, so it cools quickly when turned off. When you are cooking several items consecutively, such as baking a pie and then roasting some meat, use the large oven. The higher thermal mass of the large oven retains the heat for cooking the meat.

A big advantage of a small oven or slow cooker during the summer is that you can easily carry it outdoors to a porch or sunroom so none of the wasted heat stresses the air conditioner. To be super-efficient, buy a combination solar/electric oven to let the sun help cook the food.

Of course, using the microwave oven is more efficient than the range oven, because nearly all the energy goes into cooking the food. The newer microwave ovens provide good results, but many foods taste better when cooked in a conventional oven.

To calculate the cost to use a small appliance, find the wattage rating on the nameplate. Divide this by 1,000 and multiply the result by your $/kwh electric rate to get the operating cost per hour. Typical wattage of the range oven element is 3,000 watts, or double that in convection mode.

If the nameplate lists just amperage, multiply it by 120 to get the wattage. For appliances with a thermostat, reducing the operating cost by about 50 percent is a good estimate.

Q: Last winter, a  1/8 -inch gap formed where the walls meet the ceiling, and I am afraid that it leaked air. In the summer, the gap disappeared. What caused this, and how can I stop it?

A: The cause of the gap in winter is temperature differences between the exposed top members of the truss and the bottom members buried in the attic insulation. These thermal stresses cause truss uplift.

This gap can leak some indoor air into the attic. It can be quite a job to fix it permanently. The easiest method to correct it now is to nail a molding strip to the ceiling. This looks better and blocks some of the air leakage.

This story was originally published September 2, 2016 at 10:55 AM with the headline "How to cook with the most efficiency."