I am looking for an accurate and reliable oven thermometer. Suggestions, please!
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Your in luck! Cooks Illustrated just did a comparison of oven thermometers and their favorite was the Cooper-Atkins Oven Thermometer that costs about $7! Second place was the CDN Pro Accurate Data Hold Oven Thermometer, but it was difficult to mount inside an oven. (Jan/Feb 2011 issue)
Personally, I don't think dial oven thermometers are the best choice (though they're better than nothing).
I have bought two of them and put them side by side in the oven and seen readings (to the extent that you can read them that precisely) 25 degrees or more apart.
I check my ovens periodically using both my Polder digital meat thermometer and a Maverick digital oven thermometer, both of which have probes that you put in the oven and connect to the digital readout panel.
The Maverick one is unusual in that it doesn't give the current temperature, it gives the average temperature over the past several minutes.
Recently I've also been using my Extech infrared thermometer, taking readings off several places on the oven wall and the baking utensil I'm using.
I've used the Cooper-Atkins for some time and have found it quite reliable.
I've wondered about the accuracy of thermometers in general — even digital ones. That said, I have a 24HP Cooper Atkins thermometer, and it seemed accurate. Its reading showed my oven was too hot by about 25 to 30 degrees (when in the 400 to 500 degree range), and this agreed with my experience with the oven cooking too fast or burning food. Cooper Atkins does say the thermometer is NSF certified, if that counts for anything.
There is a significant delay before the thermometer comes to thermal equilibrium with the oven, though. When the oven signals that it's reached 400 F, for example, the thermometer will probably read around 350 F or so. Come back 10 to 15 minutes later, and it would read 430 F.
My 24HP broke after just a few months. (Don't read too much into this sample of one. It's probably just a fluke.) It's under warranty, but since it would cost just as much to mail it in as it would to replace it, the warranty is pointless for me. (Chef's Toys, which is local to me, sells it for $4.60.) DrillSpot.com has it for $5 with free shipping, though it's out of stock the last time I looked.
I could be wrong, but I thought all NSF certification meant was that it was made of food-safe material and had nothing to do with the accuracy.
My actual concern over dial thermometers has to do more with their precision rather than their accuracy. When 300 degrees and 350 degrees are only a 1/4 inch or less apart on the dial, how closely can you be measuring the temperature.
In contrast, digital thermometers are probably TOO precise, because a reading of 305.7 is not that much more useful than 305.
My experiments over the years (as well as some common sense about how ovens work) suggests that at any point in time there is a range of temperatures present. In other words, it is hotter in some places than in others.
Since for the most part the oven measures the temperature at just one place, and since oven heating elements (even gas ones) don't have instantaneous response times, what they try to do is come up with an average temperature that meets what the dial calls for, but that means there are points where the temperature will be higher than what the dial calls for and points where it is lower than what the dial calls for.
And of course, that's the temperature at the place the oven measures it, which will differ from the temperature elsewhere in the oven.
In engineering terms, this higher/lower cycle is called hysteresis. (Vibeguy wrote a nice note on this concept recently.)
What you want is an oven where the high isn't TOO high and the low isn't TOO low, but of course they don't tell you that in the fancy brochures or even the technical specs. That's why switching ovens is such a major learning process.
I remember struggling with it in a class on feedback systems when I was an Electrical Engineering student back in 1970. (That was the quarter that I decided to change my major to Computer Science.)
Use a Taylor which you can get at this fab kitchen store Fante's
My technician told me I bought the most accurate and reliable one on the market, and the thermometer was within two tenths of the technicians special proble. Good luck
The downsides of digital oven thermometers are that you have to deal with the probe and the wire. Also, using it in a really hot oven (400 or more) is usually not advised, because prolonged exposure to high temperatures can damage the probe or the wire. (Many of the digital oven thermometers won't read above 375 anyway.)
OXO makes an analog oven thermometer that looks like it might actually be readable:
Another thing to consider is whether or not you are using a baking stone. You know the stone will heat much slower than the air in the oven. I have a digital thermometer with a probe on a long wire. I place the probe directly on the stone when pre-heating, and it takes 30-45 minutes for the stone to reach the proper temp.
Thanks for all the thoughtful replies. You gave me a lot to consider.