Install Expansion Tank Hot Water Heater Video
A standard tank water heater can stress your plumbing pipes by the normal thermal expansion that happens during the heating process. A safety device known as a water heater expansion tank (sometimes called a thermal expansion tank) can help minimize the risk of pressure damage to the plumbing system. (This is normally not a problem on modern on-demand, tankless water heaters--only tank-style heaters are subject to this problem.)
The water heater expansion tank serves as an overflow receptacle by absorbing excess water volume created by the tank water heater when heating water, as well as absorbing fluctuations in the incoming water supply pressure. Since water expands when it is heated due to thermal expansion, the water heater creates extra water volume every time it heats water. It's estimated, for example, that the cold water in a standard 50-gallon water heater expands to 52 gallons when heated to 120 F. This extra water volume can create excess pressure in the plumbing system, and if the increased pressure is enough it may, over time, cause damage to the water heater, plumbing fixtures and the water pipes themselves.
Closed Water Supply Systems
I'm interested in the best place to put an expansion tank in my cold water line with a new tankless water heater install. Currently with my tank water heater (to be replaced), an expansion tank is located right next to the cold inlet to the unit. Shut off power supply and cold water supply to the water heater. Drain water from the water heater by opening a faucet or other fixture. This must be left open to prevent vacuum build-up in the water heater. Install the WH or WHV tank as shown by teeing into the the cold water line. Make sure that all joints are leak free. Tank Precharge.
In an open system where expanding water can push back into the city water supply, there is rarely any problem. However, many homes have a closed water supply system, which is a water system equipped with a one-way valve such as a backflow valve, check valve or pressure-reducing valve. In a closed system, this extra water pressure from thermal expansion can cause the most damage because the extra water pressure cannot push back into the city water supply and therefore has nowhere to go.
Most cities require that residential closed plumbing systems be equipped with expansion tanks. If you have some form of backflow preventer installed on the main water line, you may be required by law to also have a water heater expansion tank installed. Check the local building code or call the building and safety department to find out.
How a Water Heater Expansion Tank Is Installed
If you do not have a one-way valve installed on the main water line and therefore do not have a closed water system, you may still benefit from a water heater expansion tank. Expansion tanks are normally installed above the water heater on the cold water line before it enters the water heater; however, they can really be installed anywhere on the cold water line prior to entry into the water heater. Having an expansion tank helps prevent dripping faucets and running toilets by keeping the extra built-up pressure in the system from reaching the fixtures and prematurely damaging them.
Water heater expansion tank prices start at around $40 and range up to nearly $200; pricing is largely dependent on the size of the tank. For most residential installations with 40- or 50-gallon water heaters, a simple 2-gallon tank is fine. The tank is quite easy to install with a normal 3/4” threaded connection. A tee fitting will have to be installed above the water heater if one is not there already.
If you are hiring a plumber to have a water heater installed, it’s a good idea to get a price for the installation of an expansion tank at the same time. It may not be much more than you are already paying if it is done at the same time. If you are installing a water heater yourself, consider installing an expansion tank even if it is not required, since the benefits far outweigh the work and cost involved.
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Before new plumbing regulations came into existence, excess water from water heaters flowed back into the municipal water supply, causing contamination. One solution was to fit a backflow valve on the heater outlet. However, added pressure overstressed the tank, causing an explosion hazard. Changes in municipal regulations now call for an expansion tank to be fitted to water heaters. These tanks are divided by a rubber membrane supported by compressed air, with sufficient space above the membrane to absorb the overflow. With the latest breakthroughs in plumbing technology, you can save money by installing a pressure tank yourself.
Household Pressure
Obtain a suitable thermal expansion tank based on the size of your water heater. Read the pressure requirement on the side of the tank; this is usually between 40 and 60 psi. Establish the household’s static pressure by attaching a pressure gauge to a threaded faucet such as a washing machine inlet or garden standpipe. Turn off all faucets and relevant appliances to get a reading of the household’s static water pressure. If it is above 60 psi or below the recommended pressure printed on the expansion tank, adjust the household's water pressure reducing valve. This is a small component fitted with a bell-shaped housing between the water meter and main household plumbing. Undo the locknut below the hex screw protruding from the top of the bell-shaped housing. Ask a friend to monitor the pressure gauge while calling you on his cell phone. Turn the adjusting screw clockwise with an adjustable wrench to Increase the pressure; counterclockwise to reduce pressure. When the pressure reaches the expansion tank’s recommended setting, hold the adjusting screw steady and tighten the locknut with a second adjustable wrench.
Tank Pressure
Check the pressure inside the expansion tank with a tire-pressure gauge pressed onto the Schrader valve on the bottom of the tank. If the reading is high, bleed off some of the pressure. If it is below the recommended pressure, attach a hand pump to the Schrader valve and pump in more air until the reading on the tire gauge coincides with the static pressure in your home. Do not use an air compressor as it may rupture the rubber bellows inside the tank.
Saddle Clamp
Locate the household water supply shutoff valve on the house side of the pipe leading from your water meter. Turn the handle all the way to shut off the water, then open a bathroom or kitchen faucet until it stops dripping, to relieve any water pressure. Use a saddle valve to provide a T-coupling attachment point on the pipe without cutting the tubing or using solder. Undo the clamp bolts, remove the upper half of the clamp and position the saddle valve on the tubing with the outlet pointing downward. Ensure the rubber gasket on the lower half of the valve is seated properly. Slide the saddle valve sideways to allow sufficient clearance for the expansion tank to fit between the valve and the water heater. Replace the top half of the clamp and tighten the clamp bolts fairly securely with an adjustable wrench; do not collapse the tubing by overtightening the clamp. Screw the piercing handle on the side of the valve clockwise all the way until the sharpened point penetrates the copper tubing. Undo the piercing handle to the fully open position. With the tank pointing downward, this configuration will support its weight without stressing the copper tube.
Installation
Wrap a short piece of Teflon tape tightly around the expansion tank's connecting thread. Lift the tank and screw it clockwise onto the saddle valve until the threads are tight. Open the household water shutoff valve and check for leaks. If water drips from the base of the piercing handle shaft, tighten its connecting union carefully until it stops dripping. Alternatively, if water seeps out of the clamp, tighten the clamp screws another quarter turn. Open the hot water faucet farthest away from the tank to bleed off any air bubbles trapped in the pipes.
References (3)
About the Author
After graduating from the University of the Witwatersrand and qualifying as an aircraft engineer, Ian Kelly joined a Kitchen remodeling company and qualified as a Certified Kitchen Designer (CKD). Kelly then established an organization specializing in home improvement, including repair and maintenance of household appliances, garden equipment and lawn mowers.
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