Hot Water Heater Expansion Tanks

Virtually, every modern plumbing code requires the installation of an expansion tank on hot water heater installations. The reason is simple. Water expands when heated. This extra volume of water needs to go somewhere. Before the widespread usage of backflow preventers, check valves and pressure reducing valves, this expanded water simply pushed the cold water back into the city water main. If your house has one of the above mentioned devices, you could have problems. These devices prohibit the flow of water from your house back into the public water system.

Without an expansion tank, the expanding water can cause your hot water heater to possibly fail because of the increased pressure. This pressure can cause serious life threatening problems as well, if you heat your water with natural gas or propane. The water heater tank can collapse around the internal flue and cause carbon monoxide to enter your home. It is serious business.

Expansion tanks are really simple devices. They contain compressed air and a special rubber bladder. When your hot water heater turns on, the water within your piping system begins to expand. This expanding water enters the expansion tank. Eventually, hot water is drawn from the system thru a faucet and the expansion tank releases the extra water into the piping system.

Expansion tanks come in various sizes. The size you need depends upon two very important variables. You need to know the capacity in gallons of your hot water heater and the water pressure of your house piping system. The capacity of your hot water heater is stamped on a label or a plate on the side of your hot water heater.

Water pressures within municipal water systems vary widely. Here in Cincinnati, water main pressures vary from 50 pounds per square inch (PSI) to over 200 PSI within a distance of a mile! This same thing may be true in your city. People with cisterns or wells control their own system pressure thru the use of electric pumps.

It is easy to determine your incoming water pressure. Many plumbing supply houses sell a little gauge that attaches to any faucet which has garden hose threads.  Or if you like, you can call your local water department. They will possibly send a technician to your house. This person has very accurate gauges which will do the same thing.

Once you have this information, visit a local plumbing supply house that sells these tanks. They will be able to provide you with the proper sized tank to suit your needs.

Be sure to follow the directions that are packaged with the expansion tank. It only takes a few moments to read them. This will insure that your tank will function properly.

If you install a pressure reducing valve to control water hammer, be sure to buy one with a bypass feature. Without this, your water heater will begin to malfunction. You will see water dribble out of the pressure/temperature safety valve without a doubt.

The reason lies in the fact that heated water expands. Without a pressure reducing valve, this expanded water can easily go right back outside to the water main. Low quality or malfunctioning pressure reducing valves block this backwards flow of expanding water.

An inexpensive expansion tank installed on the cold water side of your hot water heater will solve this problem. The tank absorbs the expanding water and then releases it once hot water is drawn from the hot water heater. They are simple yet effective devices.

Installing an Expansion Tank

The first thing you need to do is to size the expansion tank according to the size of your hot water heater. The tank manufacturers make this easy. All you have to do is to determine the capacity of your hot water heater. This is always stamped on the side label of the hot water heater. You may have a 50 gallon or 80 gallon or whatever size hot water heater. Take this information to your plumbing supply house to get the right sized expansion tank.

A Simple Tee Fitting

The expansion tank installation requires you to install a simple tee fitting in your cold water supply line. I like to install these on a horizontal run of pipe, not a vertical piece. A vertical piece of pipe can cause undo stress on the connection point between the tank and the supply piping. I always hang my water-heater expansion tank above the horizontal pipe and recommend NEVER to hang it below. However, ALWAYS read the instructions provided by the manufacturer.

The tanks simply have a threaded connection. You will install the opposite type threaded adapter to your tee fitting. Apply Teflon tape or pipe dope to the male threads and screw the tank onto the fitting. To get a tight fit, you may have to use a pipe wrench or a leather belt around the tank. Most tanks come with a place to attach a tightening wrench. Follow the instructions and this can be done in 1/2 hour or less!