Mechanical Insulation Simple Calculators: A Guide to the Estimate Time to Freezing for Water in an Insulated Pipe

Ronald L. King

August 1, 2013

As a part of
efforts by the Department of Energy’s Advanced Manufacturing Office to improve
the energy efficiency of the U.S. industrial and commercial sectors, the
National Insulation Association (NIA), in conjunction with its Alliance
partners, worked to design, implement, and execute the Mechanical Insulation
Education & Awareness Campaign (MIC).

As we have discussed in
previous articles in this series, the MIC is a program to increase awareness of
the energy efficiency, emission reduction, economic stimulus potential, and
other benefits of thermal insulation for mechanical systems. An integral component
of the MIC was the development of a series of “Simple Calculators.” The
calculators, listed at below, provide users with instantaneous information on a
variety of insulation applications in the industrial/ manufacturing and
commercial markets.

  • Condensation Control—Horizontal Piping

  • Energy Loss, Emission Reduction, Surface
    Temperature, and Annual Return

  • Financial Returns

  • Estimate Time to Freezing for
    Water in an Insulated Pipe

  • Personnel Protection for Horizontal Piping

  • Temperature Drop for Air in an Insulated Duct or Fluid in an
    Insulated Pipe

The calculators are available
online as part of the National Institute of Building Sciences’ Mechanical
Insulation Design Guide (MIDG),
.You can also access
them through a link on NIA’s website: The calculators are fast, free, and
functional tools that make it easy to discover energy savings, financial
returns, and other information for the design of mechanical insulation systems
for above-or below-ambient applications.

This article will provide an
overview and guide to use the Estimate Time to Freezing for Water in an
Insulated Pipe Calculator.

Estimate Time to Freezing for Water in an
Insulated Pipe Calculator

This calculator estimates the time it takes for a
long, fluid-filled pipe (no flow) to reach freezing temperature.

It is important to recognize
that insulation retards heat flow; it does not stop it completely. If the
surrounding air temperature remains low enough for an extended period,
insulation cannot prevent freezing of still water or of water flowing at a rate
insufficient for the available heat content to offset heat loss. Well-insulated
pipes, however, may greatly extend the time to freezing. Clean water in pipes
usually supercools several degrees below freezing before any ice is formed.
After freezing begins, the latent heat of fusion must be removed. Note that the
calculator estimates the time to reach the freezing temperature of water (32°F)
and does not address the supercooling or latent heat of water. The calculator
also ignores the thermal resistance and capacitance of the pipe wall. This
calculator is based on the approach published in the 2009 ASHRAE Handbook of
Fundamentals (Chapter 23, Equation 1). For further information on this topic
and the calculator, please refer to the MIDG, Design
Objectives—Freeze Protection web page.

Calculator Inputs

The calculator requires Input Information for 6
input variables. Results are updated as each input variable is entered.
Following are the instructions and additional information for each input

  • Line 1. Initial Temperature of Water in Pipe, °F 42

    The default value
    is 42°F; however, you should enter the actual initial temperature for the water
    in the pipe.

  • Line 2. Ambient Temperature, °F -18

    The default value
    is -18°F; however, you should enter the expected ambient temperature in
    Fahrenheit. It is suggested you use a realistic worst-case scenario.

  • Line 3. Select Pipe Sizes or Tubing Sizes, Pipe Sizes, NPS

    The default
    selection is Pipe Sizes, NPS; however, you should use the drop-down box to
    select either Pipe or Tubing applications.

  • Line 4. Select Nominal Pipe or Tubing Size, 6

    The default value
    is a nominal pipe size of 6″; however, by using the drop-down box you can
    select a pipe or tubing size from ½” to 24″.

  • Line 5. Select Insulation Thickness, 2

    The default
    thickness is 2″; however, you should use the drop-down box to select the
    desired thickness. It offers a range from .5 to 4 inches.

  • Line 6. Select Insulation Material, Polyisocyanurate (-297°F
    to 300°F)

    The default
    material is Polyisocyanurate; however, you may use the drop-down box to select
    1 of 8 insulation materials: Calcium Silicate, Cellular Glass, Elastomeric,
    Fiberglass, Mineral Wool, Polyethylene, Polyisocyanurate, or Polystyrene. You
    will note each of the material options contains a general operating temperature
    range. The Simple Calculators do not have the capability of utilizing
    user-supplied thermal curves. Thermal conductivity values for the listed
    materials are based on ASTM material specification values.

upon the information variables provided, the Results section displays the
estimated time to freeze point in hours; in this example the result was 10.6

summary, the Simple Calculators are intended to provide the user with online,
easily accessible, snapshot information on some the most frequently asked about
benefits and design considerations of mechanical insulation systems. They do
not address every insulation material or application condition, but they do
provide guidance in a number of applications that are useful for the testing
and evaluation of insulation projects and materials.

Whether you need basic insulation information or are
designing a complex insulation system, the MIDG, found online at,
is an excellent resource for the novice or the experienced user. The MIDG
is continually updated and always has the most current and complete
information, including the convenient Simple Calculators, which were designed
to make common mechanical insulation calculations easy for users of all levels.
These tools can be very helpful in designing a mechanical insulation system and
allow the user to easily determine the many benefits and value of thermal
insulation for mechanical systems.