The HVAC Factor: Insulation For Chilled Water Piping

By William A. Lotz, P.E.
from the July/August 2015 Issue

As a professional engineer, my preferred method to evaluate various insulation products has always been field thermal performance test data. Laboratory tests may provide data to the third decimal point, but field tests give you data in the real world. Over the years, I have published field test data on a -100°F insulated heat exchanger, several cold storage warehouses, and a power boiler test of three insulation products.


My consulting experience ranges from Honolulu to Maine, and I’ve seen that moisture failures and severe mold are most frequently in the hot humid areas of the United State. However, I do see many expensive moisture/insulation failure/mold/rot/corrosion issues in New England and in the Midwest.

A recent series of tests has been conducted on various chilled water pipe insulations in-situ to determine the relative efficiency of the various products. The three test sites were commercial operating facilities in South Texas, South Florida, and Houston, TX. The insulations were installed by mechanical insulation contractor employees. All of the insulations were installed using procedures specified by the design engineer and using the factory furnished vapor barrier jacket.

The cellular glass insulation in the test was installed in 1980. All of the other insulations were installed after 2000. The ASJs (All Service Jackets) on the glass fiber, phenolic, and polyurethane pipe insulation were covered with mold indicating the insulation surface temperature was below the ambient dew point as a result of the water in the insulation. Table 3 test data shows substantial heat gain through three of the insulations as a result of moisture condensation within the insulation. This is an important issue but more important is that the facers on these three insulations were covered with mold. Only the cellular glass insulation did not absorb condensation and hence did not result in thermal degradation. Only the cellular glass pipe insulation facer was pristine even after 25 years in service.

All of the tests discussed here were non-destructive using a FLIR Systems ThermaCam with a heat flux transducer.

chilled-water-pipe-insulationTable 1 shown at right is the central piece of this research (Click to enlarge). The various insulations (three of the four) gained moisture from the ambient air, reducing the thermal value of the pipe insulation. The phenolic insulation gained from 400% to 1000% moisture reducing the insulation’s effectiveness. The polyurethane insulation gained 1000% and up in heat transfer. The glass fiber insulation gained from 400% to almost 700%. The cellular glass remained the same with no moisture/thermal gain.

This test data shows that heat transfer through the pipe insulation into the chilled water system has increased by 400% in the glass fiber insulation. For the polyurethane, the heat transfer has increased almost 300%. Under these circumstances the system owner will be paying more to run the chiller system. This test data was on piping at the South Texas test site.

ASJ Vapor Barrier Significant

The fragile ASJ vapor barrier is the major factor in the thermal performance of glass fiber, phenolic, and polyurethane insulations. When the ASJ is damaged or corrodes, it is only a matter of time until the insulation fills up with condensation and fails (except for the cellular glass).

Many years ago, I was responsible for the development of the pipe insulation vapor barrier now known as ASJ. At that time, ASJ was a lamination of white paper, fire resistant adhesive, glass fiber scrim, and 1 mil (.001″) aluminum foil. Since then the aluminum foil has been reduced to one-third mil (.00035″). It does not take much to cause tiny pinholes in the foil, which increases the perm rate from the advertised .02 perm to .04 and up to .16 perms (William A. Lotz “Facts about Thermal Insulation,” ASHRAE Journal, June 1969).HVAC-InsideArticle2

Table 2 indicates that the first three pipe insulations are rather dependent upon the vapor barrier/retarder facer for the thermal performance of the insulation product. Perm-Inch is the rate at which water vapor travels into the insulation. Obviously, the polyurethane product will last longer on a cold pipe than the glass fiber or phenolic products before they fill up with water. The cellular glass material will last indefinitely.

Where there is a constant vapor drive on the insulation on a 45°F+ chilled water pipe it is easy to see why three of the insulations fail when the thin ASJ vapor/retarder barrier is not ideal. Once the ASJ is breached, the downhill slide (see Table 3) in the thermal performance of three of the insulations is just a matter of time.

Installation Methods SignificantHVAC-InsideArticle3

On the South Florida building in this research, that timeframe was only 90 days. The insulation on the chilled pipes in that facility failed so quickly due to several factors.

  • Insulation was too thin (1″).
  • In several areas in the building the pipe fitters installed the supply and return pipes too close and they could not be insulated separately.
  • The pipe insulators work was not great (insulating chilled water pipes must be done very carefully with attentions to details: insulate valve and valve handles, insulate stem of thermometers and gauges etc.).
  • In some areas the other trades used the insulated pipes instead of ladders. This damages the thin vapor barrier.
  • Some unions, tees, ells, etc. were not carefully vapor sealed.

These above points were not unusual. I see the same poor specs and workmanship all over the United States on chilled water.

The test data shown in this article is probably typical for buildings in the U.S. Gulf Coast and Florida where the temperature and humidity are higher than in most of the U.S. In a previous paper (ASHRAE Journal April 1989) I defined “hot humid climates” as areas listed in the ASHRAE 1% standard design criteria of 90°F dry bulb with 76°F or higher wet bulb. In the U.S., this includes the Gulf Coast, Florida, and coastal areas from Washington, DC south to Florida. Three of the four insulations tested lost thermal value over time due to condensation in the insulation.

The author has seen this phenomenon repeatedly over the past 50 years of consulting on pipe insulation. Specifiers should be aware that there are huge differences in the thermal performance, over time between the popular pipe insulations.

The author appreciates the assistance of Alan Neely with the test data.

chilled-water-pipe-insulationLotz is a professional engineer with consulting clients throughout the U.S. and Canada. He has been an ASHRAE member for more than 50 years and is an ASHRAE Fellow, Life Member, and Distinguished Lecturer. His career includes spending many years responsible for a major insulation manufacturer test laboratory.



  1. I appreciate the information on insulation for chilled water piping. I would agree that it is important to ensure that you take care of the chilled water piping insulation so that you don’t end up getting mold in it. My mom is thinking of having some chilled water insulation put in, I will be sure to share this information with her.

Comments are closed.