Q&A / 

Anti-Scald Tub and Shower Faucets

DEAR TIM: My wife has requested that I install a new anti-scald tub and shower faucet. I told her that I could eliminate the possibility of scalding by simply turning down the temperature on the hot water heater. Will this work? Do the anti-scald valves really work, and if so, just how do they regulate the water temperature? P. G.

DEAR P. G.: Beware! Turning down the temperature on your hot water heater is not the answer. Installing an anti-scald valve is the best way to minimize your chances of being scalded by hot water.

Hot water is a real danger. A person can receive a blistering second degree burn in several seconds as water temperatures approach 150 - 160 degrees F. It is a very real possibility for water to leave your water heater at or above this temperature, even though your water heater's thermostat is set at a much lower temperature.

The cold water which enters your hot water heater does so through a long tube called a dip tube. This tube extends almost to the bottom of the hot water heater. The thermostat for virtually all hot water heaters is located near the bottom of the tank. Herein lies the problem.

Water temperatures within hot water heaters are not always uniform. In fact, there can be a huge difference in temperature between the water at the top of the tank and the cold water entering the bottom of the tank. The temperature difference at the top of the tank, away from the thermostat, can be up to 30 degrees hotter than the thermostat setting. This means that if your thermostat is set at 120 degrees F, water can leave the tank at up to 150 degrees F.

Some anti-scald valves can protect you against this danger. However, it requires a specialized thermostatically controlled valve. The problem is, a large majority of anti-scald valves purchased by homeowners and plumbing contractors are not this type. The most popular anti-scald valve currently sold is a pressure balance type valve. Current plumbing codes allow either type to be installed.

The pressure balance valve controls water temperature by sensing pressure differences between the hot and cold water pipes that feed the valve. You can get scalded by pressure differences. If you happen to be showering and another individual somewhere else in the house turns on a hose or flushes a toilet, the pressure and volume may change in the cold water line leading to the shower faucet. This may cause the temperature of the water coming from the valve to increase, even though the hot water was not turned up.

However, pressure balancing valves have a slight drawback. When they are installed, they have a high temperature limit stop which allows you to set the maximum temperature of the water which comes from the shower head. This setting is based upon the temperature of the water leaving the hot water heater. If you make an adjustment on the thermostat of your hot water heater, either up or down, after you have installed the valve and adjusted it, the temperature of the water coming out of the shower or tub faucet will be directly affected. Remember, the pressure balance valves react to pressure, not temperature.

The ultimate tub and shower faucet is one that can adjust for both temperature and pressure differences. These valves can be expensive. They also have minor drawbacks as well. Once you have selected a water temperature, often it can't be readjusted unless you turn the valve completely off.

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