If your current water heater is not equipped with an expansion tank, the addition of a water heater expansion tank can benefit your system. High pressure in a water heater can lead to problems such as leaks, ruptures, and corrosion within your system, all of which can be expensive to fix. While a water heater expansion tank is an added cost, it can save you money in the long run by preventing these problems.

Hot water is a widely regulated utility, with many governing agencies having a say in the design and temperature setpoint of any given system regardless of the industry or application. Below are the most common regulatory bodies involved with water temperature, and readers are encouraged to confirm their applicable requirements with local building officials, licensed mechanical engineers, and/or licensed plumbing contractors.

A thermal expansion tank will need to be replaced once every five to ten years. The best way to elongate the life of an expansion tank is to ensure the tank’s pressure matches the incoming water pressure. This preserves the life of the bladder and prevents leak issues with valves. Regardless of how well a tank is maintained, it will need to be replaced at around the ten-year mark.

• ASSE - the American Society of Sanitary Engineers publishes standards aimed at preventing unsanitary design in plumbing systems. Most thermostatic mixing valves will be specified as compliant with an ASSE standard, as this is the most widely adopted spec by manufacturers and code inspectors.

• OSHA - federal and state-level Occupational Safety and Health Administration offices issue standards that often reference other regulations, integrating these requirements together for the specific purpose of protecting worker safety.

Many commercial and industrial applications call for heated water at a temperature safe for human contact. Facilities often install high-temperature central hot water systems for a variety of technical reasons, and this high-temp water produced must be tempered down to safe levels before connecting to sinks, showers, hose stations, and manufacturing equipment. To perform this tempering work, we turn to thermostatic mixing valves, a class of valves that blend hot and cold water streams together on the fly to achieve a desired intermediate water temperature. In this article, we'll discuss the purpose and function of thermostatic mixing valves, including installation tips and regulatory considerations.

Thermostatic mixing valves are mechanical devices that connect to hot and cold water sources, and by regulating the proportion of hot to cold water blended together within the valve, they automatically provide tempered discharge water at a specific temperature. Inside the valve, a spring-loaded thermostat dynamically adjusts the amount of hot and cold water flowing through the valve, with the spring tension set to achieve the desired outlet temperature (either adjusted by an operator or set constant at the factory).

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• ANSI - the American National Standards Institute is a nonprofit organization that publishes voluntary consensus standards that many code enforcers, manufacturers, installers, and end users choose to adopt.

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4. Isolate from Other Thermal Sources - mixing valves rely on their internal or external thermostat to properly achieve the desired outlet temperature, but if the thermostat is being influenced by adjacent hot or cold thermal sources, the valve could miss its target.

Different manufacturers will have different requirements for the installation of their thermostatic mixing valves, though there are a handful of universal best practices to keep in mind, including:

1. OEM Requirements - follow the manufacturer's installation and maintenance requirements explicitly. Some details such as orientation and straight piping lengths can impact the valve's ability to reliably hit the desired outlet temperature, or worse, could risk dangerous failure. Even if two different models physically appear similar, check the manual - they may have important internal differences that impact installation.

• Thermal Losses - hot water will drop in temperature as it sits in storage tanks and flows through distribution piping, so is often generated at higher temperatures in order to tolerate shedding heat during transit but remain above the desired minimum end-use temperature.

To check a thermal expansion tank’s pressure, you can use the same pressure gauge that you use on your car’s tires. Follow these steps to discover the pressure within the tank.

The overall cost of a water expansion tank installation, including the cost of the tank, averages a little over $200. The ease of access to your system affects the labor cost of installation, as well as the size of the expansion tank being installed. An expansion tank can be installed without a professional, but you risk additional costs if you install the tank incorrectly.

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All thermal expansion tanks contain an air valve called the Schrader valve that looks similar to the air valve on a tire. Bleed a small amount of air out of the Schrader valve. If air comes out, the tank is operating correctly. However, if water leaks out of the valve, the tank’s bladder has ruptured. A ruptured bladder cannot be repaired, so the tank must be replaced. At this stage, it is recommended to check the tank’s pressure to ensure that the bladder or other tank components are not at risk of damage.

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3. Minimize Discharge Leg Distance - once tempered water is produced through the mixing valve, it must flow to the point of use through its discharge piping. If this discharge leg is too long, tempered water will take a relatively long time to push out the residual cold water in that leg and make it to the point of use. Especially for sinks and eyewash stations where immediate tempered flow is expected, mixing valves should be installed as close to the fixture’s inlet connection as possible.

If you do not use hot water for an extended period, observe the water pressure coming out of the next fixture where use hot water. If the water surges out faster than normal and calms down shortly after, there is pressure buildup within your system, and the expansion tank may be at fault. Many other factors, such as faulty water pressure regulators, can cause pressure fluctuations within a system. Consequently, this method is unreliable in determining if an expansion tank is faulty. However, it is a warning sign that should prompt further investigation into the problem.

With proper installation and calibration, a water heater expansion tank is a reliable safety feature of any water heater. Even if an expansion tank fails, failure within the tank is less expensive and problematic than failure within a home’s plumbing. Consequently, the benefits of thermal expansion tanks outweigh their negatives.

• Energy and Consumption Efficiency - compared to non-recirculated hot water lines from hot water heaters, thermostatic valves cut water waste and energy consumption by reducing the amount of time an operator has to draw water before it hits the desired temperature.

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• Microorganism Defense - domestic water is highly susceptible to microorganism and bacterial activity (notably legionella), especially at warm temperatures which drive rapid spore propagation. Heating water above this spore growth temperature range can inhibit and destroy these microorganisms.

Water heater expansion tanks can fail easily. As a result, it is a good idea to test if your tank is working if you believe something is off in your system. You can perform simple tests that indicate high water pressure in a system, or you can test the pressure inside the tank itself.

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2. Hydraulic Design - thermostatic valves are not just selected for their pipe size, but also for specific hydraulic conditions such as pressure, flow, temperature, and fluid properties. For example, hydraulically undersized valves can cause pressure and flow issues, and oversized valves can lead to poor temperature regulation.

Expansion tanks are required by code in all new water heater installations in closed systems. A closed water system uses check valves, backflow prevention devices, pressure-reducing valves, or other devices on the supply line to prevent water from being sucked back into the municipal water supply. In 1992, the EPA required municipal water suppliers to protect their lines from backflow contamination. This means homes must incorporate check valves to prevent water from backing up into the supply lines. As a result, these homes are closed-loop systems, so all new water heater installations must incorporate a thermal expansion tank alongside the water heater.

To recap, hot water systems used in commercial and industrial applications often generate hot water at a higher temperature than needed for reasons rooted in energy efficiency, water-borne illness defense, and regulatory compliance. Large systems may produce over 140°F water in order to stave off legionella blooms, but this water must be stepped down to safer temperatures before the water is discharged for human contact (typically 80°F to 120°F). Other process applications will have different temperature profiles. Thermostatic mixing valves provide a simple mechanical solution for blending hot and cold water streams to create this tempered discharge. When installed correctly, in full compliance with applicable regulatory requirements, and properly maintained, thermostatic valves can operate behind the scenes providing safe, consistent, on-demand tempered water for the life of your commercial or industrial application.

A water heater, like many things, is only noticed when it is not working. In 2007 and 2008, videos of water heater explosions went viral, and many viewers became concerned about the safety of their home water heater. Around the same time, building codes were updated to accommodate the excess pressure inside these systems. One of these updates involves the use of expansion tanks with water heaters to relieve pressure caused by thermal expansion. Below you can find information about what water heater expansion tanks are, whether they are necessary, their pros and cons, and how to test for a faulty expansion tank.

Water Mixing Valve

To raise the pressure inside a water heater expansion tank, you will need a small tire hand pump. Ensure that you do not use a motorized pump, as it may increase the pressure too rapidly, causing the bladder to rupture. Pump small amounts of air into the tank at a time. Measure frequently to ensure the pressure does not rise above the desired PSI and stop immediately once the appropriate pressure is reached.

• Local Municipal and Public Health Codes - local building departments are the most direct regulators of hot water temperatures in new and remodel construction projects. Local and regional public health departments are often the regulating bodies charged with ongoing enforcement where public health is involved, such as with food manufacturing and restaurants.

• Industry Guidelines - a wealth of information specific to certain industries and applications can be found through industry trade associations, non-profits, national laboratories, and academic sources.

When a water heater expansion tank is installed, its pressure must be set to match the incoming water pressure. Expansion tanks are pre-charged to about 40 PSI, but the pressure must be adjusted based on the home’s water pressure. If the pressure within the tank is too high or too low, it can cause the tank to fail. Should this happen, the rest of your plumbing system risks being damaged by high water pressure. You should check the pressure on your expansion tank at least once each year. Throughout the life of the tank, the pressure inside should remain consistent with the pressure it was initially charged with upon installation.

Let's answer with an example application. A large industrial manufacturing plant may have four separate cleaning areas throughout their facility that require 120°F water to wash off products between production steps. A central hot water system is installed to supply hot water to these areas. The system itself has to operate at 140°F (for reasons we'll explain below), so thermostatic mixing valves are installed at each cleaning room to blend 140°F hot water and 60°F cold water together to create the 120°F tempered water desired. With this example in mind, now to explain the challenges being addressed by setting the central hot water system at a higher temperature than the end-use temperature:

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The size of your water heater expansion tank should be based on the capacity of your tank and your home’s water pressure. The capacity of your water heater will be printed on the tank’s exterior, and your home’s water pressure can be measured with a pressure gauge. An expansion tank that is too large for the system will not adversely impact its performance. If you are unsure if one size of expansion tank will be large enough for your system, you can size up without fear of negative effects.

Now that you know your expansion tank’s pressure, you may need to lower or raise the pressure inside. To lower pressure within the tank, allow small amounts of air to escape, checking the pressure inside the tank after each interval. Once the pressure matches the desired PSI, you are finished.

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A water heater expansion tank, also known as a thermal expansion tank, is a small overflow tank that compensates for the thermal expansion of water inside a water heater. As the temperature of water increases, the water expands. Without relief, the pressure inside the water heater will increase, causing damage to valves, plumbing, or the water heater itself. Prior to the requirement of check valves, excess pressure would force water back into the municipal water lines. Regulations on backflow have necessitated the use of check valves or other similar devices to prevent contamination of the public water supply, but they have also placed greater stress on water heaters. Thermal expansion tanks solve this problem by accommodating overflow water that results from this added pressure.

• National Industry Codes - certain nationally regulated industries will have their own requirements, such as the United States Department of Agriculture's standards for food manufacturing facilities.

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• Regulatory Compliance - given the above point, substantial regulatory and legal requirements govern water temperature as a function of public health and employee safety.

Water heater expansion tanks are so beneficial to your home’s plumbing system that they are now required by code. Thermal expansion tanks provide the following advantages to your water heater system.

Using a metal object to tap the exterior of the expansion tank can give you a clue that something is wrong, but it should not be used as a final determiner. In a properly functioning expansion tank, water will fill the bottom of the tank, and air will fill the top. Lightly tap the top and bottom of the tank with a metal object. The sounds these sides give off should be distinctly different from each other. If the sounds are similar, the tank may not be filling as it should.

• National and State Building Codes - nationally-recognized building codes such as the Uniform Building Code (UBC) and International Building Code (IBC) are adopted and enforced by states that don't otherwise publish their own state building code.

If you do not have a water heater expansion tank in your home because the system was installed before they were required, you may wonder if an expansion tank should be installed in your current system. While water heater expansion tanks are extremely advantageous, they do possess a couple of disadvantages.