Pre-installed oven thermometers, as the name suggests are built into an oven and, in most cases have a temperature display on the outside control surface of the oven.
A stand-alone oven thermometer is bought separately and placed in the oven. These standalone devices come in many different shapes and sizes. Take a look a sample of suitable Comark thermometers here.
Oven thermometers work on what is known as “point principle” They take a reading from a particular part of the oven. They are positioned and calibrated to give an accurate reading of the cooking temperature of the oven.
This is an important distinction. The heating element, oven walls and oven door might all have slightly different temperatures that vary up and down from the cooking temperature. Therefore, the positioning and calibration of an oven thermometer is important to ensure it reflects the mean cooking temperature rather than one of these outlying temperatures.
The oven thermometer should, of course be visible through the oven door without need to open it. For ovens with opaque doors then you will need to use a thermometer with an oven proof external probe.
Placing an Oven Thermometer
Most food is best positioned for cooking in the centre of an oven. Therefore, to get the most accurate reading, an oven thermometer should be placed on the middle shelf. There will be hooks or bracing bars above or below the oven thermometer allowing it to be either hung from shelf or cantilevered to sit on top of a shelf.
Calibrating an Oven Thermometer
For your own peace of mind, and to ensure the thermometer is correctly positioned it can be calibrated and checked prior to first use. To do so, follow these simple steps
Place the oven thermometer in the correct position in the oven as described above or in the thermometer’s instruction guide.
Set the oven to 180°C and allow the oven to pre-heat for 20 minutes.
Without opening the door, take a temperature reading
Over the next hour take 3 more readings, one every 20 minutes.
If the thermometer and oven are working correctly the readings should fall in a range between 160°C to 190°C[is_usa320°F to 374°F[/is_usa] with the average temperature of all four readings no more than 5°C from 180°C.
A deviation from this may indicate a problem with your oven and it should be checked by a qualified service engineer.
If you have consistently lower temperatures, check the ovens heating element / gas burners and the door seal. These checks and any subsequent repairs should be carried out by a qualified service engineer.
Oven Thermometers in Fan Ovens
Cooking temperature is reduced in fan ovens by approximately 20 degrees Celsius. This is due to the more even cooking temperatures.
For an oven thermometer, this reduction should be reflected in the readings you take while cooking or during testing/calibration.
Each oven may differ, so for a more exact idea of the range of temperatures your own fan oven works at please consult your manufacturers handbook.
The unique issue to look out for in terms of failure with a fan oven is the fan itself. Periodically check that the fan is working in accordance with the oven manufacturers handbook.
Cleaning your Oven Thermometer
First check that you do not have specific cleaning requirements for your oven thermometer by referring to its user handbook and following the guide given there.
Failing that, the face of an oven thermometer should normally be cleaned with washing up liquid. In most cases it should be possible to soak the face of the thermometer in warm soapy water to loosen any stubborn grease or food stains without causing any damage to the thermometer.
If this does not work, or the thermometer is not suitable for immersion, then a paste of baking soda and water can be applied to the face of the oven thermometer and allowed to sit for fifteen minutes before being wiped off with a paper towel.
Avoid wire wool, or textured kitchen scrubbers as this may damage the face and, over time, make it hard to read.
Take a look at Comark’s range of oven thermometers here.