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My wife suspects the oven temp is not correct, she was baking cookies and had one tray near the bottom of the oven and another in the middle.

The bottom cookies got burned and the oven temp was 100 degrees over the set temp, I suggested she had the lower tray to close to the flame and that's probably what raised the temp over her set temp.

John Neville
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    I tried to write an answer based on your story, but you might want to make the question you are asking more clear--otherwise, people might vote to close the question as "not a real question" having no clear answer. – SAJ14SAJ Feb 01 '13 at 18:18
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    Yes, what is your actual question? How to tell whether the oven is broken? Whether putting a baking sheet at the bottom can increase the temperature by 100 degrees? – Cascabel Feb 01 '13 at 18:19
  • You did not turn on the convection fan? Or is it broken? Or you do not have a convection oven? – Cynthia Feb 04 '13 at 00:18

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If you truly suspect your oven is not at the proper temperature, the only thing to do is buy or use an oven thermometer, and check--remembering that the temperature will vary from slightly below the set temperature to slightly above as the cooking cycle turns on and off. "Slighty" could mean up to 25 F or so in this context.

If your oven is truly at the wrong temperature, you can either learn to adjust the setting to accommodate, or get it serviced.

All ovens are going to have a natural temperature gradient in the air depending on the position. It will be slightly hotter at the top than the bottom. Hot air rises through a process called convection. Furthermore, idiosyncratic patterns of convection are going to create local hot and cool spots depending on the volume of air flow. These will vary based on the shapes of the items in the oven at any given time.

Side note: so called convection ovens just have a fan or two to increase further the air circulation and minimize the temperature gradient while making the conductive transfer of heat from the air to the food more effective by exposing the food in the oven to a greater volume of air per unit time. That is, the fans power the convection, rather than just the buoyancy of hot air doing so.

However, ovens don't heat just through the heat of the air—they also heat through radiant (infrared) heating from the floor, walls, and ceiling of the oven enclosure. The closer an item is to the enclosure surface--especially the floor for ovens where the heating element or burner is at the bottom. and/or the ceiling if there is a heating element at the top—are going to receive more radiant energy. If there are multiple items (such as trays of cookies) in the oven, they will essentially cast "infrared shadows" on each other, so the items directly exposed to the radiant heat will get much more than those not directly exposed (there is some re-radiation from the items themselves, but lets not get complicated...)

In order to even out these effects, almost all cookie recipes where you have two trays in the oven at the same time recommend swapping the trays between shelves and rotating the front-to-back orientation half way through baking.

If you have the patience, I find that baking only one tray at a time is extremely effective.

SAJ14SAJ
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  • +1 Your answer is thorough and good but I would re-arrange the advice to OP to this: check the oven accuracy first. Since OP knew that the temp was 100 degrees over set temp, they must have an oven thermometer. After confirming oven is heating to set temp appropriately, I'd highly recommend your pan placement/rotation strategy. – Kristina Lopez Feb 01 '13 at 18:34
  • Thanks for the comments, the wife does have an oven temp Gage hanging on middle shelf and it reads within 25 degrees of set temp. – John Neville Feb 01 '13 at 18:38
  • sorry hit the wrong button, This oven has a flame on bake on both sides of the oven, and one of the cooky trays was right over the flame on the botton(that shelf was laying right on the base of the oven) causing the cookies to burn black causing the hanging temp gage to read 100 degrees over set temp. I told her that this was probably why the temp on the oven hang gage was 100 degrees over set temp, I don't think the temp actually raised and the burned cookies are the reason why the temp was reading high on her hanging gage. – John Neville Feb 01 '13 at 18:46
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    Yes, you *really* do not want to bake cookies directly on the oven floor, even with a cookie sheet. Middle shelf for single trays, or shelves at 1/3 and 2/3 height for two trays is the usual way. But that should not effect a thermometer in the middle of the oven--charring cookies don't release much heat comparatively. Something is still strange here. – SAJ14SAJ Feb 01 '13 at 18:52
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    @KristinaLopez Done. – SAJ14SAJ Feb 01 '13 at 18:53