Why One Handle Shower Valves Are Better Than Separate Hot and Cold Valves

Staff MgmtPlumbing

Every year, thousands of people suffer serious thermal shock or scalding injuries in their bathtubs, sinks, and showers. Additional untold numbers become ill due to water-borne bacteria, such as Legionella.

These are very common problems when your bathtub or shower has the old two-handle (hot and cold) shower valve. The simplest solution to this problem is to install a single-handle shower mixing valve with a pressure-balancing feature. The valve is designed such that if the cold or hot water pressure drops, the mixture still stays relatively balanced.

Did you know that if you have an old two-handle shower valve, you are not keeping current code requirements? As of January 1, 2011, Houston plumbing codes P. 2802.2 for Scaling Protection and 420.0 for Shower and Tub-Shower Combination Control Valves require Thermostatic mixing valves that control water temperature in new Houston homes, many of which have old shower systems and need to be replaced. Getting a Thermostatic mixing valve installed in your home not only will help you meet these requirements, but also ensure that you have the utmost safety and comfort when using your water.

How It Works

The valve uses a thermostatic engine that is paraffin-based to keep a fairly steady exit temperature. If the water in the valve gets hotter than the set point, the paraffin expands rapidly, moving the valve hold to let more cold water in. If the water temperature drops below the set point, it then contracts, causing the valve to let more hot water into the mixture. If there is an interruption in the hot or cold water supply due to a failure of the cold or hot water supply, the valve will shut off completely. Because of the way it works, you get safety and comfort automatically.


Having a Thermostatic Mixing Valve installed in your home isn’t the easiest thing on the planet, but it definitely isn’t the most painful experience either. However, when dealing with these types of installations that require cutting drywall and soldering pipe, we recommend using the experienced, trusted hands, and of a John Moore technician. Plumbers will need to solder copper pipe to install the valve. We like Moen’s mixing valves, such as their M-Pact Thermostatic Mixing Valve 4796 ($119.10 MSRP), or their Moen 104465, which is a high flow mixing valve ($136.55 MSRP). Delta makes great and affordable mixing valves as well, like their R10000-UNWS MultiChoice Universal Tub and Shower Valve, which is only about $40 MSRP. According to Joe Bany, John Moore’s Plumbing Manager, and technician, the process is not hard but does require experienced hands to do it right.

“It’s not an incredibly elaborate install, but it does need to be in the right location,” Bany said.  “For the most part, I definitely suggest that it’s installed professionally because it needs copper and welding and soldering so it functions properly. It’s not expensive at all when you consider what it’s protecting against.”

Here are the things that getting a Thermostatic Mixing Valve installed for you and your family will take care of once and for all:


Scalding incidents happen mostly in people’s homes- a danger while showering for anyone, especially the elderly and young children. Children, the disabled, and the elderly don’t react as quickly as others can to really hot water, making them more susceptible to burns. Injuries due to scalding are extremely painful, and can affect the victim for many years. Joe Bany said that getting up to code and installing a thermostatic mixing valve will prevent this from happening and keep you and your family safe.

In some cases, the water heater thermostat is damaged, or sometimes can simply be set too high. Also, temperature regulating valves at the household hot water source can be either faulty or not there altogether. Because Water heaters are normally set to temperatures over 140°F to prevent the development of harmful bacteria, there is a huge risk of scalding if there is no automatic temperature control, as there is with a thermostatic mixing valve for your shower. Water at temperatures above 106°F is painful for us, so at a temperature of 140°F and above, a small child can be burnt in a matter of seconds.

Thermal Shock

Have you ever had a close, dangerous call when reacting quickly to a sudden change in your water’s temperature while enjoying a shower? Have you ever slipped and fallen, even hurt yourself? This is what is known as thermal shock, and it happens more often that you may think- especially with old, two-handle valves that many Houstonians have in their homes that tend to change the temperature at a simple flush of a toilet. Thermostatic mixing valves will maintain and limit mixed hot water to a comfortable and safe temperature, helping to minimize thermal shock.

Ideally, if the supply of cold or hot water is lost, the water flow should be shut down immediately. That’s where the new and improved thermostatic mixing valve comes in. Termination of flow of the cold or hot water will eliminate the instinctive but super-dangerous reaction to move away quickly from a too hot or too cold water stream.

Legionella Bacteria

Legionella is a somewhat common water bacterium that exists in many surface water sources such as lakes, rivers, streams, and ponds. It can also be found in ground water sources and some soils, which don’t usually threaten public health. However, when the bacteria enters a household water system, it can find the perfect host environment of warm water temperatures, inactive water areas (think storage tanks and dead-end piping legs) and plenty of food sources (things like sediment, scale, and biofilm) for them to keep growing and reproducing. Under these conditions, Legionella is able to quickly colonize and form higher concentrations that can threaten the health of you, your family, and others in the community.

A widely accepted and preferred method of controlling this bacterium is to keep the hot water system storage temperature constantly at or above 140°F. Unfortunately, the elevated temperature necessary to minimize the growth of and kill Legionella bacteria has the potential to cause serious thermal shock and scalding injuries. A Thermostatic Mixing Valve will maintain and limit the mixed hot water to a desirable, selectable temperature while still allowing for the storage of domestic hot water at the higher temperatures necessary to reduce the risk of Legionella growth in your system.

Even Superman Has a Plumber

You may think that you have the hang of your old, two-handle shower system and know all of its nicks and knacks, but it only takes one unguarded moment to hurt you or someone you love. Basically, you aren’t Superman (or woman!) and unexpected things do happen all the time that we didn’t really think would or could. All the things we mentioned are serious threats that can go undetected or just ignored for quite some time, so we urge you to look into how your system is functioning and whether it’s time to consult a trusted John Moore technician. Call John Moore today to learn more about what you can do to be on the way to showering comfortably and with peace of mind that you are clean and safe!