Hot Water Systems

Tips on consulting, designing, inspecting and troubleshooting plumbing systems.

I have been involved with consulting, designing, inspecting and troubleshooting plumbing systems for more than 37 years. About 22 years ago, I started writing for this publication. I became more involved with code and standard writing organizations at the urging of an old friend, Pat Higgins, who authored this column for many years when I was writing the “Designer’s Guide” and “Classroom” columns. After Pat passed away, I was asked to write the code update column because I had attended the Code & Standard meetings for several years.  

Over the years, I have written many articles about hot water systems. I have also served on most of the hot water temperature control device standard committees and attended many other committee meetings dealing with water heaters and temperature controls with various standards writing organizations. 
I often get calls about plumbing systems that have been designed, installed or maintained poorly, leading to property damage, injuries or death. By far the two most common problems that I get calls for deal with domestic hot water systems. They are: scalding when the water is too hot, and Legionnaires disease from improperly designed, installed or maintained hot water systems.  

This article will focus on the scalding issue, although, a properly designed system will simultaneously control scalding and Legionella bacteria growth. When someone gets scalded there are typically severe injuries or death, and it usually leads to litigation. As they look for information on scalding and temperature controls, they usually come across one of the articles I have written. The calls typically deal with a scalding incident involving a child, elderly person or disabled person. Unfortunately, many of the incidents result in serious injuries and death.

Statistics have shown that the majority of scald burns occur to children, the elderly and disabled persons because they have physical or mental limitations that prevent them from getting out of harm’s way or comprehending what is happening when scalding hot water is allowed to flow from a shower, bathtub or sink faucet.  

Scald burns are 100 percent preventable if the domestic hot water system is designed, installed and maintained properly. 

The model plumbing codes require compensating type shower valves with temperature limiting valves at the source fixtures, and they give temperature limits at various fixtures, however, the model codes do not address hot water storage or distribution temperatures. Except in the case of combined domestic hot water and heating hot water systems, they simply require a mixing valve to limit the hot water distribution system temperature to a maximum of 140 F, which may not control scalding or Legionella based on other design factors. We have the knowledge to develop a hot water system design to prevent both scalding and Legionella bacteria growth, which can lead to Legionnaires’ disease, but it is not covered in the plumbing codes.  

It seems everyone turns to the plumbing codes as a source of design information, yet the codes are a minimum and do not address hot water system design. We need to recognize the need for an industry design standard, code requirements or a solution that is comprehensive and system-wide to control both Legionella bacteria growth and scalding. Controlling only one aspect will not provide complete protection. We need to maintain hot water temperatures high enough to “pasteurize” or “disinfect” the hot water in the storage and distribution system while also monitoring cold water supplies to ensure adequate water treatment chemicals to control bacteria entering the water system.  

Water conservation efforts are allowing water treatment chemical to dissipate to levels that are ineffective at controlling bacteria growth in building water systems. We also need to reduce to temperatures that will not cause scalding while maintaining distribution temperatures above 122 F and addressing system pressure fluctuation to prevent thermal shock or sudden changes in temperature with pressure balancing or thermostatic elements that can prevent slips and falls in a showering environment.  

Scald burns often require extensive medical treatment and follow-up burn care that is very expensive. As the burns become more severe and depth of the burn, or the percentage of the body surface area burned, increases, the chances of death increase. Burn injuries are probably one of the worst injuries a person can sustain, and burn victims often live with constant, severe pain from damaged or burned nerve endings, loss of elasticity of the scar tissue and psychological issues associated with being disfigured.  

I have also dealt with many cases where the parents or guardians were investigated for child abuse because it was perceived that the scalding was intentional abuse. There are some cases where the injuries were purely accidental. 

In these cases, there are many signs that can point to foul play or indicate it was a terrible accident. However, Child and Protective Services (CPS) workers don’t always know what to look for, and from my understanding, they do not have it in their budget to hire an expert. If the hot water is kept well below 120 F, most scald injuries would not occur. If the temperatures are maintained below 110 F, it would be difficult, if not impossible to have a scald injury. 

When I say “maintain” the hot water temperature, it means maintained by a master thermostatic mixing valve or digital mixing valve and by adjusting the limit-stop on a tub/shower valve. Many untrained individuals think that maintaining the hot water temperature means adjusting the thermostat on the water heater. The thermostat on a water heater does not control the outlet temperature of a storage type water heater and should not be used to control the hot water distribution temperature. The model plumbing codes prohibit the thermostat on a water heater from being used as the final temperature control to prevent scalds.  

The American Society of Sanitary Engineering (ASSE) is in the process of developing a new standard (ASSE 1082) for water heaters that have the ability to control the outlet temperature of the water heater.  The first draft has been written, and it appears there is some more work to be done. But the preliminary discussions indicated it would be for a water heater to be certified to control the outlet temperatures of those indicated in the ASSE 1017/CSA B125 mixing valve standard. This standard allows up to a seven degree temperature fluctuation above or below the set point for whole-house or hot water distribution system applications. 

There was discussion of another standard to develop a new ASSE standard (ASSE 1083) for temperature control for instantaneous water heaters to meet the requirements of the ASSE 1070 standard for point-of-use temperature control, which has tighter temperature control requirements for point of use water heater applications. For more information, contact Conrad Jahrling at ASSE.

A scalding  nightmare

A mother brought her school-aged child to the emergency room because he was screaming in pain from scald burns. Emergency room staff immediately sedated him to ease the pain. They never asked what happened. If the question was asked, it is likely this story would have a different ending. The child eventually died, and protective services workers built a case against his mom when it was apparently just a terrible accident. 

The mom lived in a doublewide trailer or manufactured home that was exempt from the local plumbing codes. The tub/shower had a two-handled faucet and a 20-gallon water heater that was turned up to the highest temperature setting. The evening of the incident, the mom prepared ther two children for bedtime by bathing the younger child, a toddler, first. Then she took the toddler in the bedroom to get dressed for bed. She laid out clothes and retrieved towels from the dryers for the older child. 

A short while later, she called the older, school-aged child in the living room to say it was almost time to come take a bath. She went back into the bathroom and turned on the water to fill the bathtub for him. 

During the delay between the first bath and the second bath, the hot water in the pipes between the tub/shower and the water heater had cooled down to a comfortable bathing temperature. She checked the water temperature in the tub with her hand for a few seconds, and it was comfortably warm. The recreation had the hot water open most of the way, and the cold water was barely opened so that it was mostly the cooled-down hot water that was flowing from the faucet.  

Getting an accurate description of her activities between the two baths was critical to establishing a timeline to determine how much the water had cooled down. The water heater was located near the kitchen and laundry area on the other end of the house from the bedrooms. She left the bathroom while the bathtub filled with water. She walked to the living room to tell her older child that the bathtub was ready for him. The timeline indicated it would have been during this time that the hot water from the water heater arrived at the fixture and caused the tub spout discharge temperature to be very hot. 

Upon resuming the water flow, she again held her hand in the water for a few seconds, and slightly adjusted the cold-water valve to fine-tune the temperature. Within 15 seconds, the water was at a comfortable temperature. It took almost 40 seconds before the extremely hot water from the water heater arrived at the faucet. 

To compound the situation, the mother went into the utility room and started a load of laundry using cold water. She used cold water to wash clothes because the family had a small water heater, and they found it better to just wash with cold water thn risk using up the hot water when bathing, dishwashing and doing laundry were done in a short time period of each other. After loading the laundry in the washing machine, she walked to her desk near the kitchen ato check her email. The cold water for the washing machine caused a drop in the cold-water pressure at the two-handled tub filler faucet and caused a significant rise in the hot water temperature at the tub filler faucet that was already set to a mostly hot position.  

Shortly after leaving the bathroom, the water in the bathtub was mostly hot water because of the pressure drop in the cold water line from the simultaneous fill of the washing machine and the non-pressure or non-temperature compensating tub filler valve.   

The tub/shower valve should have been a pressure balancing valve, thermostatic valve or combination pressure balancing and thermostatic valve, and it would not have allowed excessive temperatures if the limit-stop had been properly adjusted and set.  

The drop in pressure in the cold water line caused the two handle faucets to allow almost full hot water temperature to flow from the faucet. The manufactured home relied on the water heater thermostat for temperature control. The water heater thermostat is not allowed to be the final temperature control to prevent scalding in most plumbing codes. However, many states have exemptions for plumbing inspections of manufactured or trailer homes because the homes are built and inspected in a factory. The factory plumbing inspection may not be compliant to the code in the state where the home will be located. This is a loophole in the codes that needs to be addressed.  

The temperature and pressure conditions that I suspected had occurred were later confirmed. An accident reconstruction specialist measured the tub and determined how the child would have been standing in order to slip and fall in the manner consistent with the injury. According to our timeline and reconstruction of the incident, he stepped into the hot water without checking the temperature first. The hot water startled him, causing him to slip, fall and hit his head on the back edge of bathtub, where he would have laid unconscious in the scalding hot water while it was still running. Eventually the flowing water drained the water heater and cooled the water in the tub.  

After the mom finished responding to some of her emails, she went to check on her son. She knocked once and heard water running. She opened the door to see him lying in the tub with his ears under water.  He was in a sluggish, groggy state, but slowly lifted his head and turned toward her. She told him it was time to get out and get ready for bed. When he didn't get up right away, she went over to the bathtub and turned the water off. She noted the water was not hot at this time and it had been draining out of the tub through the bathtub overflow. She added that the water temperature in the bathtub was lukewarm.  

She helped her child sit up and noticed the skin on his shoulders seemed loose and slippery. It was pinkish but did not look burned or blistered. Many serious scald burns do not look bad at first. As she tried to get her him to stand up, he regained consciousness and started crying out in pain. The mother noticed loose skin on other parts of his body. 

They lived in a rural area, and it was a relatively long distance to the hospital, so she called a nearby friend to watch her other child, and she wrapped her injured son in a blanket and took him to a nearby hospital emergency room. The ER staff met her at the car and wheeled him into the ER. When they took off the blanket, much of the child’s skin came off with it. They also found a large bump on the back of his head. This discovery prompted an automatic call to a CPS investigator. 

A few hours later, CPS workers had their first look at the child in the ER. He had lost a significant amount of skin and was covered in bloody and large blisters. The CPS workers approached the mother in the waiting room and asked her to take them to her home to investigate the incident. 

From that moment on, her life was turned upside down. She was grieving for her injured child, worrying about her toddler, trying to locate and notify her husband of what happened, and now the police and CPS were treating her as the suspect in a crime. As time progressed the burn injuries worsened, and the CPS worker became more aggressive with prosecution. Eventually, the child died, and CPS and prosecutors filed murder charges.  

I asked if I could speak with the mother at her home to ask her in detail to show me what happened that day. There were no burns on her. There were no signs of a physical struggle. There were no scrapes or scratches on her, and only a bump on the head and scald burns on her child. She was brought to the home for the inspection from the county jail in handcuffs and leg shackles. They brought her into the living room and sat her down while I interviewed her. She cried as I her asked questions and took notes. 

She was told me what happened that evening. I asked her to go into the bathroom, laundry room and bedroom and describe everything in as much detail as possible. I told her that I needed to recreate the events of that evening so I could develop a timeline with respect to what happened with the plumbing system. 
I made notes and reenacted everything as she had described it, and my investigation revealed how the hot water temperature could have felt like an ideal temperature for bathing based on the time lag between baths. I was able to install digital and analog temperature and pressure recording devices and recreate the conditions of that evening based upon my interview with her and provide a report for the defense.  

After the reenactment of what happened that evening, it was obvious it was simply a terrible accident where all the conditions were ideal, and the stars aligned for this scald incident to occur. 

Ron George, CPD, is president of Plumb-Tech Design & Consulting Services LLC. Visit

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