Boiling Water Method for Testing Accuracy

If you need to test the accuracy of your thermometer, one of the standard procedures is to use the boiling water method. This method works well for occasional testing of a small number of thermometers. When working around the boiling water, take care not to burn yourself as you’re testing the thermometer.

• The boiling point of water is 212°F (100°C) at sea level. In order to determine the boiling point of water at your elevation, there are several charts available online that will tell you exactly or you can use the general guideline of a drop of 0.9°F (0.6°C) for every 500 feet (152.4 meters) increase in altitude. For example; the altitude of Rochester, NY is 502 feet, therefore, the boiling point is 212 - 0.9 = 211.1°F. 2.

• Bring a clean container with at least 3” of water to a rolling boil.
• The pot can be any size; it just needs to be big enough to cover at least 2” of the thermometer stem.

• Ensure the stem is immersed past the groove on the stem (a minimum of 2").
• For 2.5” length stem, this groove may be just under the threaded connection.
• For best results, suspend the stem of the thermometer in the water so that it’s not touching the bottom.

• Allow a minimum of 3 minutes for the reading to stabilize
• Gently tap the case prior to taking the reading.

• Every Tel-Tru thermometer is calibrated before shipping. All models that have an "R" at the end of their name can be adjusted by using the external reset feature.
• For 0.25" stem diameter models such as the BQ300R, click here.
• For 0.15" stem diameter models such as the BQ325R and LT225R, click here.

Commercial Use
Alternative methods, such as the Tel-Tru Check-Set^® dry block calibrator, may be more appropriate for commercial settings where testing is done frequently. Testing can be done on the NIST traceable device by simply selecting the test temperature and inserting the thermometer..