Print this page Print this page

Thermowells Basic Selection Criteria

David A. Snyder, P.E.

Course Outline

This course familiarizes the reader with the basic selection decisions that must be made in order to select the proper thermowell for each application.  Standard lengths for temperature sensors and thermometers are discussed to help the reader choose a combination of thermowell process insertion length, lagging length, and extension length to fit an off-the-shelf temperature sensor or thermometer.  There are many illustrations and several examples to clarify the meanings of terms like process insertion length and lagging length.  This course gathers together the far-flung pieces of information about thermowells and arranges them in a cohesive, easily-understood presentation.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

Intended Audience

Anyone who is involved in the specification, procurement, or installation of thermowells, or the temperature sensors and thermometers that are installed in thermowells, will benefit from this course.

Course Introduction

Thermowells are present in almost every industrial process but they are rarely discussed in any depth or with any completeness.  The formula for calculating the sensor length for a given thermowell is very simple, but the derivation of that simple formula is not usually presented.  The fragments of information that are available from widespread sources have been gathered together and arranged in this easy-to-understand course that includes many illustrations and several examples. 

Course Content

The course content is in a PDF file:

Thermowells Basic Selection Criteria

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the file size, we recommend that you first save the file to your computer by right-clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader from your computer.

Course Summary

Upon successful completion of the course, the reader will have a thorough understanding of standard thermowell lengths and how the sensor length is determined for each type of thermowell.  The reader will be familiar with the decisions that must be made in order to select the proper thermowell for each application.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.