How Much Does a Water Heater Expansion Tank Cost?

$145 – $350, Installed

The cost to install a water heater expansion tank ranges from $55 and up for the rare DIY project, to about $350 when a pro adds an expansion tank to a large residential water heater.
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Average Cost of a Water Heater Expansion Tank Installation

To hire a plumber in your area, expect to pay an average cost of $265 to have an expansion tank added to your existing water heater. This will include the tank, all plumbing supplies, installation labor and inspection where required.

Average Do It Yourself cost
$55
Average Contractor Installed Cost
$265
Typical Cost Average
$145 – $350, Installed

hot water heater expansion tank cost

Overview of Water Heater Expansion Tanks

Thermal expansion tanks are now required by code for most water heaters using municipal water. This is a result of new codes that require backflow valves to be installed preventing water from your home to flow back into the municipal supply. The valve creates a closed system in which pressure can build.

If you replace your water heater or sell your home, you’ll need to add one to the system. The tank will also protect your water tank, plumbing and fixtures from the increased pressure of a closed system. There’s more information below in About Water Heater Expansion Tanks.

This cost estimate page, or Costimate, covers all potential costs for DIY or hiring a professional. These include job cost factors, retail expansion tank cost and installation labor costs. Prices from a few other reliable cost estimating sites are listed. The information should allow you to make a good cost estimate of what your project price will be.

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Product and Installation Supplies Cost Details

Expansion Tank Price Factors

Thermal expansion tank cost on a water heater is determined by these factors.

  • Who Installs the Tank – Most of the cost to install a water heater expansion tank is in the labor. If you can DIY, the savings will be about 75%.
  • Type of Tank Support – As simple metal or plastic strap to support the tank’s weight costs a few dollars. Steel brackets can cost 3-5 times as much as the tank.
  • Cost of the Tank – There are small cost differences in the prices of the 2-gallon to 5-gallon expansion tanks common to residential installation. Quality is also a factor in tank cost.
  • Installation Factors – When the water tank is easily accessed and there is room to work, installation charges may be lower than when, for example, the water heater is in a cramped crawlspace or utility closet.

Cost of Expansion Tank Installation Supplies

The size tank required is based on water heater capacity and the pressure of the incoming water supply line, this is especially important if you have a well pump. Most expansion tanks are less than 5 gallons, since residential water heaters range from about 30 to 100 gallons. Look for a lead-free tank rated for potable water.

Online sellers like Supply House have calculators or charts showing what size tank you’ll need.

Pro Tip: It’s always better to have a tank that is too large than one that isn’t large enough. When in doubt between two sizes, pick the larger tank.

Here are retail expansion tank and installation supply prices.

  • $35 – $70 | Residential Expansion Tanks, 2.0 to 5.0 gallons
  • $50 – $200 | Steel Tank Mounting Bracket
  • $6 – $12 | 30-foot Roll of Metal Hanging Strap
  • $15 – $25 | Pipe Cutter
  • $12 – $20 | 10” to 14” Pipe Wrench
  • $3 – $8 each | One ¾” Connector
  • $2 | Copper Tee
  • $6 – $8 | Short Section of Copper Pipe
  • $2 – $4 | Teflon PTFE Pipe Tape
  • $4 – $8 | One copper female threaded union
  • $25 – $40 | Soldering Kit, (pros prefer soldered connections to a “shark bite” connector)
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About Water Heater Expansion Tanks

Here’s why you might need a thermal expansion tank.

Water expands when heated. For example, 40 gallons of water at 60F becomes about 40.6 gallons at 120F, creating significant pressure inside the water tank and pipes.

In older water systems, that extra capacity was pushed back into the municipal water system, an open system. No problem.

By the early 2000s, most cities and counties required check valves on residential water lines to prevent this. These regulations produced closed systems that gave expanding water nowhere to go. The increased pressure often damages the water tank, pipes and fixtures. One plumbing contractor says, “I have seen several cases where pipes or water heaters split due to the pressure…so the expansion tank IS necessary if you have backflow preventing devices.”

Hence, adding a water heater expansion tank became a common indoor home improvement project when connected to “city water.” If you build a new home or have an inspector in to check the installation of your new water heater, you’ll probably have to add an expansion tank to meet code.

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Permits, Inspection, Related Costs and Installation Time

Permits and Inspection Cost

  • $0-$125 | In most counties, no permit is needed for the installation of an expansion tank. If the installation is part of installing a new water heater, then a permit might be required. Your local building department can let you know if a permit is required.

Related Costs and Installation Time

Hiring a licensed plumber is your best bet for having the job done correctly the first time. However, an experienced handyman might do a good job too.

Here are labor ranges for each:

  • $75 – $150 per Hour | Plumber Rates
  • $60 – $100 per Hour | Handyman Rates

This is a quick job for most pros:

  • 1-2 Hours | Time to Install a Water Heater Expansion Tank
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DIY or Hire a Pro?

steve-hansen

Installing a water heater expansion tank is moderately difficult. Here are the basic steps to help you evaluate whether to tackle it or call a pro.

First, you’ll need the tools and supplies listed in the Retail Costs above.

The expansion tank goes on the incoming supply line. Most installers place them directly above the hot water tank, so the expansion tank is horizontal. This is the easiest way to apply a metal support strap.

However, anywhere on the supply line after the water shut-off valve is OK. The expansion tank can hang vertically as long as it can be supported.

Thermal expansion tank installation step by step:

  1. Turn off the water, and open a spigot to take water pressure off the line.
  2. Turn off power to the water heater and/or shut off the gas by turning the valve to the closed position (the handle will be perpendicular to the gas line).
  3. Have a bucket handy to catch any water left in the supply line. Cut the supply line using a pipe cutter to get the cleanest cut.
  4. Install the copper Tee on the supply line, and solder it in place, if necessary.
  5. Attach the thermal expansion tank. Wrap the threads in 4-6 loops of pipe tape. Thread the connector onto the expansion tank, and attach the other end to the Tee.
  6. Use metal strapping to support the weight of the expansion tank, nailing both ends of the strap to the floor joist above.
  7. Turn on the cold water supply. If there are no leaks, turn on the water heater and gas, if it is gas fired.

Watching a pro do it, as seen in this video, will also prepare you for the project.

Is This a DIY Project? What do You Think?

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