A water heater expansion tank is a crucial component in modern plumbing systems, designed to mitigate pressure buildup caused by thermal expansion. This guide details the installation process, necessary tools and materials, and considerations for determining the appropriate tank size. The installation process involves turning off the water supply, connecting the tank to the cold water line, and verifying the system for leaks.
Understanding the Need for an Expansion Tank
In closed plumbing systems – those containing a check valve or backflow preventer – water has nowhere to expand when heated. This expansion creates pressure spikes that can damage water heater components, cause leaks at pipe joints, and prematurely activate the temperature-pressure relief (TPR) valve. Many building codes now require expansion tanks, particularly for tankless water heater systems, though they are recommended for all water heaters to prolong system life and prevent potential damage. An expansion tank functions by providing a space for the expanding water to enter, compressing a pocket of air within the tank. When the water cools and pressure decreases, the compressed air pushes the water back into the plumbing system, maintaining consistent pressure.
Tools and Materials Required
Successful installation requires specific tools and materials. The following list is based on common installation requirements:
- Pipe wrench
- Channel-lock pliers
- Teflon tape
- Drill with bits
- Expansion tank (properly sized)
- 3/4″ copper tee fitting
- Copper pipe (short sections)
- Mounting straps/brackets
- Dielectric water heater union
- 2 3/4 inch copper female-threaded unions
- Plumbing soldering equipment (if needed)
- Copper flex pipes (if needed)
- Additional 3/4-inch copper fittings (as needed)
Determining the Correct Expansion Tank Size
Selecting the appropriate expansion tank size is critical for effective pressure management. A typical 80-gallon residential water heater generally requires a 2.1-gallon expansion tank. For water heaters exceeding 80 gallons, a 4.8-gallon expansion tank is usually necessary. Tank size correlates directly with the amount of pressure that can be safely released from the water heater. To ensure accurate sizing, it is recommended to consult the tank manufacturer’s sizing chart or seek guidance from a water system expert.
Installation Procedure: A Step-by-Step Guide
The installation process involves several key steps, ensuring both safety and proper functionality.
- Preparation: Begin by turning off the power supply to the water heater. This can be achieved by unplugging the unit or switching off the corresponding circuit breaker.
- Water Supply Shutoff: Locate the home’s main water shutoff valve and turn it to the “off” position.
- Workspace Preparation: Ensure the area around the water heater is clear and accessible.
- Tank Pressurization: Before connecting the tank to the plumbing, it is essential to pre-charge it to match the home’s water pressure, or slightly above. Use a pressure gauge to determine the home’s water pressure. Compare this reading to the pre-charged pressure of the tank, typically found under a cap on the bottom or side of the tank. Adjust the tank’s pressure using a standard air pump, setting it to 5–10 psi above the home’s water pressure to account for potential pressure loss over time. This step must be performed before any water enters the tank to ensure an accurate setting.
- Thread Sealant Application (Optional): Applying plumber’s tape to the threaded fitting on the tank’s connection can enhance the seal and reduce the risk of leaks. Wrap the tape clockwise around the threads 2–3 times, ensuring it lies flat and does not extend beyond the fitting’s edge.
- Tank Connection: Thread the expansion tank onto the pipe fitting by hand. Hand-tightening is generally sufficient, especially if thread tape has been applied. Avoid using tools to overtighten, as this could damage the tank or the connection.
- Plumbing Integration: The expansion tank is typically installed directly above the water heater, spliced into the cold water delivery pipe using a tee-fitting. The tank can be mounted vertically or horizontally, depending on available space and the tank’s specifications.
- Water and Power Restoration: Once the tank is securely installed, slowly restore the water supply by turning the main water shutoff valve back to the “on” position. Then, restore power to the water heater by plugging it in or switching the circuit breaker back on.
- Leak Check: Carefully inspect all connections for leaks. Address any leaks immediately by tightening fittings or reapplying Teflon tape as needed.
Expansion Tank Installation Costs
The approximate cost of an expansion tank installation ranges from $30 to $70 for materials, plus the cost of labor if a plumber is hired. A thermal expansion tank itself typically costs between $25 and $60, depending on size and model. Plumber’s tape or thread sealant costs less than $1, and a mounting bracket or support strap (for horizontal installation) costs under $10. Professional installation by a plumber can add $100 to $300 to the total cost, varying based on local rates and any necessary adjustments to existing piping.
Identifying the Need for Expansion Tank Replacement
Expansion tanks, like all plumbing components, have a limited lifespan and may require replacement over time. Several indicators suggest the need for replacement:
- Closed-Loop Plumbing System: If the plumbing system includes a backflow preventer, check valve, or a water meter with a built-in check valve, an expansion tank is essential.
- Pressure Spikes: Experiencing water pressure spikes when hot water is used indicates the expansion tank may be failing to adequately manage thermal expansion.
- Temperature-Pressure Relief (TPR) Valve Activation: Frequent or unexplained activation of the TPR valve suggests excessive pressure buildup, potentially due to a malfunctioning expansion tank.
- Visible Tank Damage: Any visible signs of corrosion, leaks, or physical damage to the tank necessitate immediate replacement.
System Types and Permitting
Water heater installation often requires a plumbing permit, which will clarify any expansion tank requirements specific to the local jurisdiction. An expansion tank may not be required for open plumbing systems, but installing one is still advisable to help preserve the home’s plumbing. Instructions should be considered general guidance, as specific installations may vary depending on the tank and plumbing system. If unsure about any aspect of the installation process, consulting a professional plumber is recommended.
How Expansion Tanks Function
An expansion tank contains a flexible rubber diaphragm that divides the tank into two sections. One section allows water to enter as it heats, while the other provides an air chamber for the diaphragm to expand into. As water fills the tank, it compresses the air, absorbing pressure without straining the pipes. When the water cools or pressure drops, the compressed air pushes the stored water back into the plumbing system, maintaining consistent pressure.
Conclusion
Installing a water heater expansion tank is a relatively straightforward process that can significantly protect a home’s plumbing system from the damaging effects of thermal expansion. By following the steps outlined in this guide, homeowners can ensure proper installation and long-term system reliability. Proper sizing, careful installation, and regular inspection are key to maximizing the benefits of an expansion tank.