oven thermometers

[marmalady]

Does anyone know how to check an oven thermometer for accuracy? I just got a new oven, and the old thermometer I had wasn't registering the same temp. as what the oven was set at. Then I got a new one, and the same thing happened; I've been fooling with regulating the temp. controls on the oven (according to the owner's manual), but to no avail; I'm wondering if the thermometers themselves are faulty.

I have adjusted the temps on instant reads, but don't see any little nuts and bolts to adjust with on the oven thermometers.

[kokopuffs]

Unless you're willing to spend literally hundreds on a well calibrated thermometer, just consider a brand new oven thermometer as accurate. Probably the oven "dial" needs resetting. IMHO (I have 4 years of college chemistry) the oven dial is considered inaccurate. So, a thermometer is always used as the ultimate reference.

I use a TAYLOR brand oven thermometer costing less that $10.00 and consider it to be accurate.

[mudbug]

Assuming your oven thermometer is water safe... to check thermometer accuracy, let stand 10 minutes in boiling water. Thermometer should read 212 degrees; if there is any variation, subtract or add to make the same degree of allowance in testing oven temp.

[kokopuffs]

Again, Cchiu, this is where chemistry applies. Altitude affects the boiling point of water. Here in Denver, the boiling temperature is far less than 212 F. Salt content of water can affect the boiling point, too. Unless pure water is used, the determination of the B.P. is useless. Just consider most well made oven thermometers as accurate - give or take a few degrees.

[mudbug]

Boiling Water Test

The most common way to test a thermometer is to place it in boiling water. An accurate thermometer will read about 212*F in boiling water at sea level under normal atmospheric conditions.

To test your thermometer, bring a pot of water to a vigorous boil. Hold the thermometer stem or probe in the water, making sure not to touch the sides or bottom of the pot, and take your reading.

Remember that there are several factors that affect the boiling point of water:

* As atmospheric pressure decreases, the boiling point decreases. Atmospheric pressure will vary depending on your altitude and local weather conditions.
* Hard water boils at a temperature 1-2*F higher than soft water, due to dissolved mineral salts.
* Using a tall, narrow pot will result in a boiling point about 1*F higher than a short, wide pot.


If you live at high altitude, you'll need to take that into account when testing your thermometer. The table below lists the approximate boiling point for a number of different altitudes. As a general rule, the boiling point decreases approximately 1.8*F for every 1000-foot increase in altitude. Note that the actual boiling point may be higher or lower depending upon atmospheric pressure in your area on any given day.

Altitude Boiling Point (F/C)
Sea Level 212/100
2,000 ft. 208/98
5,000 ft. 203/95
7,500 ft. 198/92
10,000 ft. 194/90
15,000 ft. 185/85
30,000 ft. 158/70

Another way to determine your boiling point is to use a Boiling Point Calculator. By entering your current barometric pressure and your elevation, you can get a good estimate of your boiling point.

[chiffonade]

Originally posted by kokopuffs
Altitude affects the boiling point of water. Here in Denver, the boiling temperature is far less than 212 F.

Four Corners here, at 7000 feet. Water boils at 190. Had to know this to do canning without poisoning people.

How about putting both of your oven thermometers in the oven, just to see if they both read the same temp? The consensus may make you feel better.

[mudbug]

marmalady,

On a tangent - Measuring Oven Accuracy

There is a wonderful article in the March 2002 issue of Cook's Illustrated. It discusses the calibration of ovens both of commercial quality and residential use and the wide variations between each oven, how they heat in what areas of the oven, how they "maintain" the target temperature, and the differences which leads to the issue of thermometers.

They end up rating thermometers and highly recommend an inexpensive oven thermometer over high priced ones.