Oven hotter at top or bottom?

anndyer

I always thought the oven was hotter at the top cuz heat rises but at KAF seminar yesterday they said it was hotter at the bottom.

badge posted by: anndyer on March 25, 2012 at 3:52 pm in General discussions
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reply by: BRYAN CARMENATI on March 25, 2012 at 3:59 pm
BRYAN CARMENATI

Why is this?

reply by: GinaG on March 25, 2012 at 4:54 pm
GinaG

Yes, I would like to know, too: Why?

reply by: Mike Nolan on March 25, 2012 at 6:06 pm
Mike Nolan

It probably depends on what heat you're measuring.

Obviously the gas burners or electric elements at the bottom are much hotter than the air in most of the oven, though hot air tends to rise.

This radiant heat can affect things close to it.

Something on the bottom rack of my oven tends to get done on the bottom before it is done on the top. The reverse is true for something on the top rack.

If you want to test this with your oven, do the following:

Get a (cheap) loaf of sliced bread. Put several slices directly on the bottom rack of a pre-heated oven. Time how long it takes for the bread to brown on the top, then see how brown they are on the bottom.

Now try the same thing with the top rack.

I have done this with all three rack positions (and for both the 'bake' and 'broil' elements) to see how even the heat is. Most ovens have hot spots, I have a pretty good idea where mine are. Do you?

reply by: GinaG on March 25, 2012 at 8:37 pm
GinaG

I do! I do! You really do need to have that information, especially when you want to brown something more or minimize browning.

The same experiment you speak of is a great way to find out how hot or not your broiler is. That also is very helpful.

If the bread browns nicely in a minute, it runs normal. If it takes longer than one minute it runs low and if it browns in 30 seconds it runs hot. You should have your bread slice(s) 6" from the element to effectively test the broiler. This is helpful to do so you can predict cooking times.

reply by: frick on March 26, 2012 at 7:08 pm
frick

This is a good topic for discussion. While the center rack is most often best for most baking, I find myself moving pizza from bottom to top to get the top of the pizza cooked properly before the bottom gets charred. What most people don't realize is that the closer you move an object to the top, the more it will top brown. I have a gas oven and when the gas comes on, things cook very rapidly on, at first, the bottom, THEN the top. I suppose there isn't that kind of variation in an electric oven.

That tip about the bread/toast browning is a good one. Thanks, everyone.

reply by: anndyer on March 26, 2012 at 8:45 pm
anndyer

Thanks...I like the bread test! Will def do it! I have stones on the bottom of my oven which I slides my loaves onto...they def brown well on bottom of loaf because of this. Always made pizzas on middle rack cuz directions say not to have any oils on stones.

reply by: lennycubfan on March 27, 2012 at 1:54 am
lennycubfan

The heating elements are usually at the bottom, so while heat rises it starts at the bottom (the top element is the broiler and self cleaning mode). Once the oven is properly heated, the heat will radiate off the top and you will have a convection thing going. And that is why pizza is best baked on a baking stone on the top rack, so the top of the pizza will brown at the same rate that the crust bakes. On a properly pre-heated baking stone the crust will bake and brown nicely no matter what rack it's on. If you're baking your pizza on a pan, the top rack might not be the place for it, I bake deep dish pizza on a pan on the lower middle rack.

reply by: ovenquestions on January 03, 2013 at 9:08 pm
ovenquestions

So as me and my girlfriend were having a fight about this. We first looked it up and you are one of the first hits in the search engine, but clearly no consensus. We ended up measuring using one of my so called "useless tools", the infrared thermometer. so the top of the oven cooking at 420F was 210*c. The bottom was 208*c. The element itself was 220*c. I took at least 10 readings of each surface. I think the reason why the top is just as hot is because its insulated, and the air inside is all bumping against eachother creating a uniform distribution of energy.

I think that a properly working oven should be uniform temperature, however i am not an oven repair man so not sure.

i did not measure two identical pans with identical pan loads.

reply by: Mike Nolan on January 04, 2013 at 12:14 pm
Mike Nolan

In case earlier posts weren't clear, the hottest part of the oven is always the bottom, because that's where the heat elements are, and they're much hotter than the desired temperature. However, by the time you get a few inches above that, air circulation starts to take effect and the temperature is lower than the heating element. The next hottest part of the oven is the very top, because hot air rises.

You'll probably never find an oven with constant even temperatures throughout the oven, because that's not how most ovens work.

The first reason for this is what engineers call hysteresis.

During a heat cycle the oven will reach a temperature slightly higher than the setting and after the cycle ends the temperature will drift down below that setting before the next heat cycle starts. In a well-designed oven the high-to-low range should be no more than about 25 degrees.

Exactly where the temperature is measured can have an impact on that temperature range. as can how the oven is loaded.

The second reason is convection currents. Heat rises naturally, and what happens is the hotter air rises to the top, forcing the cooler air back down to be heated by the heating element/burners. How well the air circulates in the oven is function of both design and how the oven is loaded.

What initially made Viking ovens so different from their competitors is that they were designed by engineers who actually measured the air circulation patterns while designing the oven to try to minimize hot spots.

As a result, if you have a three-rack oven, for example, and you use a standard 12 x 17 cookie sheet on all three racks, the middle one will get the least heat, both because it's in the coolest part of the oven and because it gets the least air circulation.

I have a good infrared thermometer (Extech, under $70 at stores like Lowes and Home Depot), and I've used it to measure surface temperatures around my oven many times, so I'm fairly familiar with where the hot spots are.

I recommend people who get a new oven go buy a few cheap loaves of sliced bread and do circulation tests. Test all the various load patterns you're likely to use, one rack, two racks, three racks, top only, middle only, bottom only, etc.

If you load all three racks, what you'll see is that the top of the bread will get brown first on the top rack and the bottom of the bread will get brown first on the bottom rack.

Try it at several temperature settings, too.

In a well-designed convection oven, the air flow is fairly uniform across all levels. Putting a single fan at the top generally won't achieve that, which is why home convection ovens are so inconsistent.

A professional convection oven will have multiple fans to circulate the air both horizontally and vertically. Some of them reverse which way the air flows periodically to try to prevent hot spots.

I haven't seen one yet, but I've been told that some of the really high end professional convection ovens work similar to an immersion circulation system. The air is sucked out, heated to the proper temperature and then blown across all levels of the oven. (That means there is no heating element at either the top or the bottom of the oven, it's somewhere else.)