In the early 1980s, I first met with Dr. Al Steele, who authored this column for many years. Dr. Steele wrote many of the plumbing design and engineering books such as “Engineered Plumbing Design,” “High-Rise Plumbing Design,” “Advanced Plumbing Engineering” and a few others that were part of the plumbing classes I had attended over the years. His books and magazine columns have been used to teach plumbing classes across the country. I even used them for plumbing design and code review classes I taught at Oakland Community College, the University of Wisconsin and the University of Minnesota.

As an officer of the Dallas/Fort Worth Chapter of the American Society of Plumbing Engineers (ASPE), in 1985, I hired Dr. Steele to conduct a Certification in Plumbing Engineering (CIPE) exam review seminar. I picked him up at the airport, we had dinner and our friendship grew as we talked about plumbing, plumbing classes that he had taught and classes our chapter was sponsoring.

Later, he used the hand-written notes he gathered for that CIPE review seminar to eventually publish the first “CIPE Exam Review Book.” I taught some CIPE exam review seminars after he retired and provided edits to the ASPE Certification Committee. Eventually, I served on the ASPE Certification Committee helping to develop certification exam questions. I developed 13 PowerPoint training presentations for ASPE chapters to use in their education programs. I also developed content and quizzes for the Read, Learn, Earn program.

Energy Conservation and Legionella

During my discussions with Dr. Steele in 1985 and at subsequent ASPE meetings, we discussed the recent clash of energy conservation initiatives and plumbing system performance issues. In the mid-1970s, energy conservation efforts developed following the Arab oil embargo of 1973 that led to lower maximum hot water storage temperature mandates.

Many Americans could not get heating oil and they waited in long lines for gasoline at gas stations as crude oil prices skyrocketed. In a panic, many well-intentioned people proposed energy conservation ideas to their governing bodies. These proposals were quickly adopted as mandatory requirements in codes and ordinances without an adequate analysis of health and safety issues or a study of the impact on system performance issues.

We experienced a similar situation following the 1992 Energy Policy Act, which mandated lower-flow fixtures without any research into Legionella growth in stagnant water, drain-line transport issues, scald issues with ultra-low-flow shower heads installed on older-style, two-handled tub/shower faucets and shower faucets with no pressure or temperature compensation.

Dr. Steele told me about the research he led as president of the American Society of Plumbing Engineers Research Foundation (ASPERF). The group had done some testing on reduced-size venting and he told me about a 1988 research project titled, “Research Report 88 – 01, Temperature Limits in Service Hot Water Systems.”

The report addressed hot water system storage and distribution temperatures related to mandates to store hot water at lower temperatures. It discussed how proper plumbing design could address scalding, Legionella bacteria growth and energy conservation concerns. Energy conservation folks seemed to think, at the time, that simply turning down the water heater thermostat would save energy and reduce scalding incidents.

He said he took a lot of flak over the energy loss calculations in that report because they were not carried out to enough decimal places to show a significant difference. Steele noted that he intentionally did not address heat loss through equipment or piping because the same energy savings could be accomplished by adding insulation vs. turning the water heater down.

In the report, he pointed out that the manufacturers based their warranties and equipment selection charts on 140 F storage temperatures. Manufacturers had not changed sizing information or warranty information based on 140 F storage temperatures despite mandates for lower storage temperatures. He said it was not clear in the report but storing at a lower temperature would require a larger tank and more surface area, so the savings at lower temperatures needed to be calculated with a larger tank and insulation type, where thickness was still an issue.

ASPERF was limited by the scope it was commissioned to do — to provide research and write a report addressing lower maximum storage temperature limits in service hot water systems, which were being mandated by the energy conservation initiatives following the 1973 oil embargo.

Although many of the energy conservation proposals in the late 1970s and early 1980s were beneficial and had nothing to do with plumbing, there were some that resulted in minimal energy savings and created a significant health and safety risk to the public while also decreasing the performance of plumbing systems. One of these mandates was to reduce the maximum allowable hot water storage temperature in water heaters to 110 F.

I told Dr. Steel that from my review of his research document, there seemed to be no consideration or research into what the conservation effects were having on the volume of hot water available. We discussed the change in the percentage of water flowing into the hot-water pipe compared to the percentage of water flowing into the cold-water pipe when the maximum hot water storage temperature is near the usage temperature. With a reduced temperature, most of the water flowing from a shower will flow through the hot water pipe.

I mentioned many other issues related to the performance of the plumbing systems or the potential health and safety effect on the public. We had a conversation about how energy and water conservation can create a cause-and-effect relationship with various water storage temperatures and piping configurations in the plumbing systems. Lower storage temperatures can cause water heaters to start to condense in the flue tubes, which accelerates corrosion of the water heater tank.

We talked about reduced hot water storage temperatures, increased hot water flow rates in the hot water pipe at lower distribution temperatures, lower water heater first-draw capability and the need for a larger storage tank when hot water is stored at lower temperatures.

The energy conservation measures were promoting Legionella growth and scalding could still occur at lower storage temperatures with thermal layering and stacking. We discussed the mixed water formula from the old ASPE Data Books, now published in the ASPE Engineered Plumbing Design Handbooks. We also discussed the reduced flow rates at fixtures, pressure imbalances associated with ultra-low-flow (ULF) plumbing fixtures that could cause thermal shock and scalding issues, temperature control delays in ULF showers (especially hand-held showers), and bacterial growth in hot water that is mandated to be stored in the ideal growth temperature range for Legionella bacteria.

Eventually, ASPERF teamed up with the University of Wisconsin to do more research, which was published March 21, 2008, in a report titled, “Scalding Temperatures Relative to Age and Physical Condition of the Person.”

ASPERF Report

Back in 1988, the ASPE Research Report identified more than 100 sources of information related to storage, distribution and application temperatures of domestic hot water concerning Legionella bacteria growth and scalding. The 1988 report also addressed:

• Background information on the oil embargo/energy crisis from 1973;

• Mandates from energy conservation programs requiring maximum hot water storage and distribution temperatures of 110 F;

• The conflict between temperatures required to control Legionella bacteria growth and temperatures required to minimize scalding;

• Legionnaires’ disease;

• Control of Legionnaires’ disease;

• The need for more research;

• Energy conservation calculations;

• Insulation discussion; and

• Conclusions: storing hot water between 135 F to 140 F to kill Legionella bacteria; and delivering hot water from fixtures at a maximum temperature of 120 F or a lower temperature to prevent scalding.

Analysis of the issues found:

•  A minimum storage temperature of 131 F is essential to prevent the spread of Legionnaires’ disease (131 F is the temperature at which Legionella begins to die).

• To assure a safety factor, the minimum storage temperature should be 135 F.

• The 110 F criterion originally adopted in the 1970s is still mandated in some codes. (These should be updated to call for storage and delivery at 135 F to 140 F with code-compliant shower and tub/shower valve’s maximum temperature limit-stop adjusted to reduce the maximum temperatures to a safe maximum showering or bathing temperature such as 110 F to 120 F, depending on the application.)

• There were unforeseen problems with temperatures set at 110 F at the water heater, such as the limit-stop must be full open when the hot water supply temperature is between 110 F and 105 F. (This can allow scalding if stacking occurs or if someone adjusts the system temperature at the water heater thermostat or a master mixing valve.)

• Water at 110 F is in the ideal breeding temperature for Legionella bacteria growth.

• Water heater sizing, selection and warranty information is based upon 140 F storage temperatures.

• Lower storage temperatures will require changing sizing criteria, selection charts and, eventually, larger equipment and an impact on the economy, which is an important consideration.

The ASPERF recommended the deletion of all references to 110 F storage and distribution from all codes, governmental regulations, rules and regulations of associations and agencies, industry standards and wherever it may appear.

It also recommended that hot water generators be 135 F to 140 F. (The new ASHRAE Standard 188 and ASHRAE Guideline 12-2000 recommend storage temperatures in this range and a minimum distribution temperature of 124 F because Legionella bacteria can grow in temperatures up to 122 F. It survives between 122 F to 131 F but does not multiply.

The energy conservation mandates requiring the lowering of the maximum allowable hot water storage temperature were adopted by the U.S, Department of Energy, ASHRAE, various code organizations and medical facility certification agencies. These agencies had quickly adopted the proposed changes during or after the energy crisis without adequately researching the effects on plumbing systems or public health and safety.

The ASPERF research report did not consider heat loss in the storage tank or the distribution piping and simply covered the issue with a note saying, “The proper selection of insulation will be the ultimate determinant as to whether energy is conserved or not.”

The energy conservation proposals at the time were well-intentioned mandates that:

1. Mandated temperature conditions in the hot water storage and distribution system ideal for Legionella bacteria growth.

2. Reduced the amount of hot water available for the first draw from a storage tank.

3. Caused a condition where the majority (almost 90 percent) of the mixed water flow came through the smaller hot water piping, causing significant pressure imbalances between the hot- and cold-water systems.

4. Increased thermal shock issues with older-style, two-handled, noncode-compliant shower and tub/shower valves (still existing in many homes), which could also lead to scalding in addition to other slip and fall or physical injuries.

Consequences

Many of the energy conservation proposals came from people outside of the plumbing industry who did not fully understand the scalding, bacterial growth temperatures and system pressure issues. They were making generic energy conservation proposals to save energy. Lowering the storage temperature of hot water in a tank would save energy but increasing the insulation thickness to the tank and circulated piping would have accomplished the same thing without creating many of the problems described here.

Shortly after implementation of the energy conservation mandates, a large outbreak of Legionnaires’ disease occurred in 1976 at the American Legion Convention at the Bellevue Stratford Hotel in Philadelphia. There were 182 cases and 29 people died. The bacterium was later named Legionella pneumophila in honor of the American Legion.

“Legion” refers to a small army and “ella” is a suffix used as a formative in taxonomic names, especially genus names of bacteria: chorella, pasteurella and salmonella. The naming of the bacteria was well-thought-out. “Pneumo” relates to lungs, “philia” refers to the city where it was first discovered but also means “loving,” so Legionella pneumophilia refers to a small army of lung-loving bacteria.

To my knowledge, I don’t believe there has ever been an investigation into a possible link between energy conservation mandates for lower maximum hot water temperatures and the original discovery of Legionnaires’ disease but it makes me wonder. The investigators at the hotel did not know what they were looking for because it was a mystery disease that was finally isolated the following year from samples taken from victims.

The source of the Legionella outbreak at the Bellevue Stratford hotel was never determined because of the long delay in determining that it was a water-borne illness. The hotel was shut down after the outbreak and was out of business. All systems had been drained and flushed or cleaned by the time of the bacteria’s discovery and its most likely transmission from an unconfirmed source to convention attendees in tiny water droplets inhaled into the lungs.

Because of the unknown source of Legionnaires’, no data was collected on storage and distribution temperatures or water treatment chemical levels, and no samples were collected from any of the building water systems during or immediately following the outbreak in 1976.

We now know that storing water at 110 F, as was called for in many energy conservation mandates at the time, can lead to an increase in Legionella bacteria growth in the hot water storage and distribution systems, which could eventually lead to outbreaks. Hot water storage tanks have taken a bad rap as the cause of Legionnaires’ disease. Storage tanks do not cause Legionella bacteria to grow unless the conditions (temperature and nutrients) are ideal for bacteria growth.

Some tankless water heater manufacturers and others have made claims that storage tanks cause Legionella bacteria but that tankless water heaters do not. Most electric or gas tankless water heaters only raise the water temperature to a usage temp between 100 F to 105 F. I have been involved in investigations where Legionella bacteria was found growing inside tankless water heaters. Tankless units still have water in the heat exchanger tubes. Many do not reach a temperature that will kill the bacteria over a required exposure time (a range between 131 F to 158 F) or disinfect the water if it can reach a temperature over 158 F to instantly kill Legionella bacteria.

Those early energy conservation programs mandated stored water temperatures in the ideal range for Legionella bacteria growth. While saving a few dollars on energy bills, many people were exposed to a serious health hazard known to cause severe illness and death. We will probably never know the actual numbers because many of those deaths were attributed to pneumonia.

The ASPERF research report included a two-year literature search that began in 1986 — it reviewed and analyzed published and unpublished information on hot water temperatures concerning Legionella bacteria growth and scalding issues. The research also investigated the advantages and disadvantages of various storage and distribution temperatures in a range from 110 F to 140 F.

In 1989, ASPERF issued a position statement based on knowledge obtained and what was happening in the industry at the time: “Hot Water Temperature Limitations: The American Society of Plumbing Engineers recommends that the outlet temperature of hot water generators be a maximum of 140 F and a minimum of 135 F for service hot water systems. ASPE further recommends that all references to a maximum temperature of 110 F in service hot water systems be deleted from all codes, government regulations, industry standards and where it also may appear. Adopted by unanimous vote of the Board of Directors of ASPE, May 6, 1989.

Original reporting: https://www.phcppros.com/articles/8259-legionella-growth-in-hot-water-systems