I have new ovens and I was told the temperature can be 10-15 degrees off and that is acceptable. I am skeptical! I just want to check...shouldn't oven temperature be right on to set temp?
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Most ovens "cycle" close to the expected temp, but some can be WAY off. Whether you have new ovens or old, it is a really good idea to have a separate thermometer in the oven so that you can see what the temp really is (and adjust the dial -- if necessary -- appropriately). Things can get particularly interesting with convection ovens. Some convection ovens (I accidentally purchased one of these!) are "dumbed down" so that the temp is actually and intentionally much lower than the programmed temp -- this is so that cooks with a conventional recipe of say "bake at 350 for 20 minutes" don't overcook if they leave in for 20 minutes (properly callibrated convection ovens will cook 20 to 30% faster than a conventional recipe indicates). Frustrates the heck out of me. With my separate oven thermometer (hung at the end of the rack so that it is visible through the oven door) I now know that when I have it on "convection bake" at 350, it is sometimes as low as 240. Amazing, huh?!
I'd be happy with 10-15F from the set point. Many ovens are off by 25 or even 50 degrees.
Understand that ovens generally cycle on and off, warming up and cooling down in the process. So even if the set point was spot-on, that would only represent the maximum (or average, depending upon how it was calibrated) temperature.
On top of that (little pun), there will be a difference between the upper half of the oven, the lower part, the rear and the front. Less of an issue with a convection oven, but there will be hot spots.
And if that weren't enough, the calibration might be correct at only one point on the dial (or display). For example, the oven may actually be 400F when it's set to 400F, but 185 at 200 and 515 at 500.
Now does any of this really matter? Meh. It's better than the old days of "hot oven" or "very hot oven" and the bread came out just fine.
As for an oven thermometer, I don't use one at home. The temp inside the food is what counts so that's where I stick my probe.
Congratulations on the new ovens!
pierino is a trusted source on General Cooking and Tough Love.
ChefOno is correct and just be happy that you don't have to deal with "gas mark 3, gas mark 4" etc. as you would in Europe. Yes, your American oven could easily be off by 25 degrees, probably on the low side. Don't believe the dial. It's done when it's done.
I could have saved myself a lot of typing with "It's done when it's done". ;-)
Get an oven thermometer. Especially if you bake. I've never found an oven that is perfectly accurate.
What kind of ovens did you get??
Second mrslarkin - get a thermometer. They are cheap and accurate.
My daughter the pasty chef insisted on an oven thermometer in my oven if she would bake here and it has made all the difference. MrsLarkin is right on.
Thanks everyone for your advice. I now have new oven thermometers. I have double wall BlueStar ovens. I wanted basic engineering and made in USA.