Updated on 01.22.12

# Turn on the Oven Light While Cooking (21/365)

Several months ago, I was curious about how much heat was lost when I opened up the oven to inspect a dish cooking in there. I put an oven thermometer in the oven, waited until the dish I was cooking was almost finished (a casserole cooking at 400 F), then opened the oven door for about ten seconds to inspect it.

During those ten seconds, the thermometer dropped almost 20 degrees. When I closed the door, the temperature slowly returned to 400 F, but during that period, the oven had to put in some extra work to return that heat.

How much? It’s really difficult to exactly calculate that without a meter running specifically for the oven. My best estimate, using a lot of math and thermodynamics, is that you lose about \$0.02 worth of energy every time you open the oven door.

My solution? I turn on the oven light when I’m cooking anything in the oven. That way, I just lean over and check what I’m cooking without opening the oven door. The light bulb uses less than a cent of energy per hour of use, so the cost is virtually nil if I flip it on, inspect the food, and flip it off.

It’s the little things – but there are some bigger tricks when it comes to energy use and your oven.

First, unless you’re desperately pinched for time, don’t start preheating the oven until the food is in there. If your recipe says “Preheat the oven to 400 F” and then later says “Bake for 30 minutes,” don’t preheat the oven at all.

Instead, put your food in the oven, then set the temperature to 400 F. Then, add about half of the preheat time to the cooking time.

Why? When you open a preheated oven to put in your dish, it’s no different than opening the oven to check the food near the end of the cooking time. You lose that \$0.02. Also, the energy used when preheating the oven isn’t actually being used for anything at all, so that’s also lost energy. Most of the time, when I’m making a meal, a few minutes on the baking time makes little or no difference, so I might as well save that energy.

Another valuable oven tactic is to multitask by using multiple racks. If I’m cooking a meal on one rack, I might as well throw in a loaf of bread or something else that can also cook while the oven is running. The extra energy used to cook the second (or third) item is much lower than the energy you’d lose by heating the oven a second time (think about the heat coming off your oven on cooldown – that’s money wasted, so why do it multiple times?).

Another simple tactic is to use glass, ceramic, or earthenware baking dishes rather than metal ones. These hold heat much better than metal pans. If I’m using such pans, I know I can drop the cooking temperature by 20 or 25 degrees or shave some total time off of the cooking just because of the more efficient use of heat.

You should also keep your oven clean, so the hot air in your oven is actually cooking your food instead of the burnt materials in your oven. You don’t have to do this every time you use it, but a regular cleaning simply makes your oven run more efficiently every time you use it.

A final tip: turn off the oven when the food is nearly done. If you leave the door closed, the oven will lose heat very slowly, allowing your food to continue cooking. I usually try to turn off the oven when there’s five or so minutes left in the cooking time. The dish almost always finishes perfectly.

These tips, taken as a whole, can significantly reduce the time your oven

This post is part of a yearlong series called “365 Ways to Live Cheap (Revisited),” in which I’m revisiting the entries from my book “365 Ways to Live Cheap,” which is available at Amazon and at bookstores everywhere. Images courtesy of Brittany Lynne Photography, the proprietor of which is my “photography intern” for this project.

1. Bren says:

That’s odd; I have never seen an oven that does not force you to have the light on. ‘light’ is always the first setting. Everything else only works when the light is on. I’m European, by the way.

2. Vanessa says:

I’ve never had an oven with a light, that’s why I open the door.

3. PawPrint says:

Thank you for the preheating tip. Sometimes if you follow a recipe verbatim, the oven has preheated for longer than necessary before you put the dish in. When I use multiple racks, I find that both of the items take longer to cook so I seldom do that. My only issue with using an oven light rather than opening the door is that some food needs to be touched (e.g., a cake that springs back or you need to stick a toothpick in to see if it’s cooked in the middle), but using the light only certainly works for food that you can just see if it’s done by looking at it.

4. Nick says:

Your advise to not preheat the oven is really horrible. It could lead to many ruined dishes for 2 cents in savings.

There are many examples, but an easy one is pizza. Starting pizza in a cold oven is maybe the worst idea in the world. Your crust will be really soggy and gross. Any toppings you put on will be really watery and soft.

If a recipe says to preheat the oven, it’s probably for a reason. I would rather spend 2 extra cents and preheat the oven then possibly ruin a 10 dollar meal…

I think advice like this is the definition of penny wise, pound foolish.

5. Izabelle says:

Really? No preheating, but adding 50% more cooking time will save you money???

First, it may not ruin a casserole, but any baker knows that leavened items require that rapid spike in temperature (an steady heat throughout) to achieve proper structure.

Also, when pre-heating, the heating elements are on at full power, and only re-light to maintain the heat during the baking. For this reason, most energy consumption happens at the pre-heating stage, and very little once the required heat is achieved. Skip pre-heating and on top of not saving money, you’ll burn the outside of your food before the middle is cooked.

For a casserole there’s no need to preheat, but for a cake it’s important.

7. Becky says:

For 2 cents savings, I’ll open the oven door. Even if I open the oven door twice daily, 365 days of the year, I’m saving \$14.60 total.

For me, that’s a lot of oven usage as I really only use the oven a couple times a week. And usually, when I do need to open the door, it’s to check something that needs touching, or even to rotate a dish or pizza pan so it bakes a little more evenly.

As others have said, whether pre-heating is necessary or not has a lot to do with what’s being cooked. Some things don’t matter, others do.

The one piece of advice I agree with is cooking more than one thing while the oven is hot. I’m unlikely to bake a batch of cookies or brownies if we’re not using the oven already… but find it much more likely if we’re already using the oven for something else.

8. Valleycat1 says:

Our oven has no window so I’ve learned to trust the timer without a lot of interim checking. I agree with the commenters about preheating being important for baked goods including pizza. Casseroles and potatoes, not so critical.

9. Cathleen says:

Preheating is required for many dishes for successful results.

I do not come here for cooking tips myself but even saving \$.02 is just silly IMO to risk ruining a dish that suggests preheating.

10. Vanessa says:

Two cents is almost half a scoop of Trent’s homemade detergent, so from his perspective, that’s probably big, big savings!

11. Izabelle says:

I don’t know if it is still the case for new ovens, but most will go a little over the target heat when pre-heating, which can also alter final results.

Rather than obsessing with such trivial details as oven light and extra oven minutes, I find that having a toaster oven as well (for smaller items) avoids about 90% of sub-optimal oven use in my house.

12. Sara says:

Wow, you kind of play it fast and loose with cooking directions, huh? These tips will work fine for some dishes, but could ruin others. Regarding preheating, most recipes say to preheat the oven before you do anything else, but if you do that, the oven will probably be hot well before you’re ready to use it. I usually wait until I’m almost ready to put the food in the oven before I start preheating it.

13. SwingCheese says:

As others have said, skipping preheating only works for certain foods. Once you figure out what they are, you can adjust accordingly. Also, we leave the oven on for the entirety of the cooking time, but once the food is done, we remove the food and turn off the oven but leave the oven door cracked open a bit, allowing the heat from the oven to escape into the kitchen. It makes the room nice and toasty (and since the insulation in our rental is negligible, that is a treat).

14. Jane says:

I do exactly what Swing Cheese does and in the winter crack the door to let the heat escape into the house. I figure I already paid for that heat, I might as well use it.

I don’t ever preheat items for the amount of time it says to, but with baking you should definitely preheat at least 5 minutes. I also turn off the heat right near the end of cooking.

But Izabelle’s advice is perhaps the best savings – use a toaster oven. I personally have not had good results baking breads or cakes in the toaster oven. After a few failed banana breads, I gave up on that. But it is excellent for the kids’ chicken nuggets or baked fish or any other thing that isn’t a baked good. We bought one that accommodates most frozen pizzas as well, so we don’t often use the oven for pizza.

15. Nate Poodel says:

My oven doesn’t have a light either.
As much as Trent likes homemade bread I’m surprised he hasn’t invested in a Bread Machine. (or maybe I missed the post) I bought one for \$29.95 at Wal-mart five years ago and it is still baking bread perfectly.

16. Jules says:

I’m in the camp which almost always preheats the oven. It’s critical for baked goods (maybe less so for casseroles), and honestly? It’s \$0.02. That’s worthwhile to have something that’s baked properly. I’ve found that, especially for goods leavened with baking soda, if you leave it sitting in the oven, they don’t rise as well–by the time the oven reaches temperature, the baking soda has already finished reacting with the acid.

And along those lines: if you have a good baking book, and it tells you to use a certain kind of pan, listen to it. Again, this probably matters less for casseroles, but the kind of pan you use can change the time spent in the oven. Glass and ceramic are great at holding heat, but they also take a while to get to temperature.

17. Genny says:

Here’s a tip….following recipe directions leads to much better results than using \$200 pots. You heard it here first.

18. deRuiter says:

#17 Genny, that is a clever remark.
Preheat the oven, follow the directions, extract perfect baked goods and other dishes at the end of the cycle. With gas heading to \$5. per gallon, saving 2 cents for imperfect baked goods results is pointless. This did fill a page in a book of 365 pages which is now being reatreaded in order not to have to think up a useful tip for a column.

19. Mister E says:

I was just going to jump in and say that preheating is NOT optional in many instances.

20. Michelle says:

To those who crack open the oven door when finished using it to let the heat out…where do you think the heat goes if you don’t open the door? Opening the door may let it out faster, but it will still escape into the room whether the door is open or not.

21. Gretchen says:

I’m starting to really hate this series.

Random pizza baking tip: put the broiler on first to get the oven as hot as possible before you start to bake.
I haven’t personally tried this, but it’s from serious eats dot com, a site whose tips I trust.

22. Riki says:

So, I recognize that I’m at a place in my life where I worry more about how I spend my time than anything else and convenience is definitely worth a price to me. I’m not worried about paying down debt as I don’t have any so I really don’t watch every single penny.

That said, I feel like this series has focused on saving pennies in very, very small increments (sometimes very hard-to-measure increments) in exchange for constantly having to think about things. It might work for some people but at this point I’m finding it a little bit repetitive. A little math tells me that saving a couple of cents a few times a day only adds up to about \$36 at the end of the year. Doesn’t seem worth it to me.

Trent, you seem to be working through one category at a time (currently cooking). Perhaps it might be more interesting if you mixed things up a little bit?

23. Derek says:

Gretchen, ditto. This series is going to get very old by June, let alone December…especially if every tip is about saving a few pennies.

24. Andrew says:

Pointless and counterproductive frugality uber alles.

25. SwingCheese says:

@Michelle: I know that the heat escapes into the kitchen with the door open or closed, but when I crack open the oven door, I can feel it more readily, and since I’m frequently cold, I enjoy it that way. But yes, the heat dissipates into the kitchen either way.

26. David says:

For those inclined to disbelieve the advice not to preheat ovens (which I hope includes all of you), take care not merely to preheat them until the indicator light goes out or your oven thermometer first shows the desired temperature. This means that the air inside the oven is at the desired temperature, but you should leave the oven for an additional ten minutes or so in order that the heat spreads evenly throughout the metal.

27. Jill says:

Pyrex specifically says you have to preheat if you’re going to put one of their glassware dishes in the oven. Failure to do so has apparently been linked with the exploding Pyrex problem, which is going to cost you a lot more than \$0.02 in labor costs to clean up if it happens.

28. Evita says:

Advice getting more bizarre by the day! Thank heavens for the comments !

29. valleycat1 says:

Taking Trent’s \$.02 cents per open door to its conclusion: assume you use the oven once every day of the year and open the preheated oven’s door once to put food in and once to check before it’s actually done. 4 cents x 365 days comes out to \$14.60. For a year. My savings would be half that because I rarely check midway through, and even less because we don’t use the oven every single day. So my savings would be less than \$10 for the year. I’m willing to have that portion of a work hour go toward escaping heat. The savings is probably even less if you’ve got a gas oven.

30. Another Katie says:

I’m not really buying that using glass or ceramic is a more efficient use of heat than metal without further study. While glass and ceramic hold onto heat better than metal, metal conducts the heat to the food inside faster.

So it seems that food in a glass or ceramic dish would stay hotter longer once removed from a heat source, but food in a metal pan would cook faster than food in a ceramic pan if both pans are cold when put in the oven.

31. Maya says:

Sounds like I came to the wrong party since I only preheat the oven for bread or baked desserts, and I’ve successfully cooked brownies when I had to turn the oven off midway through because I had to leave the house. I figure: why bake nothing during that time unless I’m baking something that requires specific temperatures for the chemical reactions to occur properly. For the same reason I don’t preboil water for potatoes, vegetables, or pasta; I just stir a little more often until the water is hot. Why waste all that energy bringing the water to a boil first?

The Pyrex thing baffles me because I cannot see how there is more risk putting a cold dish into a cold oven and letting it all heat up together compared to putting a cold dish into a hot oven. The latter seems more risky to me.

32. David says:

Ten seconds to leave the over door open seems to me an extraordinary length of time. Open the door, take the dish out, close the door… three seconds tops, I’d have thought.

Of course, better still might be to trust your culinary skill and your high-quality pot to cook the food without your having to look at it until you put it on the table. Besides, what on Earth will looking at a casserole tell you? It will look the same as it did an hour ago, but at that time the ingredients were still almost raw. Believe the recipe, leave the oven light off (thus saving about \$0.003 a century) and don’t worry about whether it needs more salt. You live in America, so everyone will add more salt to their own portions anyway.