How Much Does a Water Heater Expansion Tank Cost?

Common Range: $100 – $500, Installed

National Average: $275, Installed

Updated: November 17, 2023. Written by: Steve Hansen

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Water Heater Expansion Tank Cost Range

The cost range of a water heater expansion tank is between $40 – $175 depending on the size of your water heater and the type of expansion tank installed.

Average Cost

To hire a plumber in your area, expect to pay an average cost of $275 to have an expansion tank added to your existing water heater. This will include the expansion tank ($40 – $115), all plumbing supplies (up to $40), installation labor ($75-$200) and inspection where required (up to $100).

Average Do It Yourself Cost
$95
Average Contractor Installed Cost
$275
Typical Cost Range
$100 – $500, Installed

hot water heater expansion tank cost

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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.

And a Temperature and Pressure valve, a T&P, is not enough either by code or by practical design. As one master plumber says at Shamrock Plumbing Company, “The T&P valve is not supposed to act for thermal expansion because of the good possibility that over time the T&P will lime up and freeze closed, making it inoperative when needed to prevent explosion.”

If you replace your water heater or sell your home, you’ll need to add one to the system. Go here to calculate the cost of water heater replacement for your specific size and type of unit. This is true even for some tankless water heaters, but only when you have a storage tank in combination with the tankless system. The tank will also protect your water heater, plumbing and fixtures from the increased pressure of a closed system. There’s more information below in About Water Heater Expansion Tanks.

Why You Need a Water Heater 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.

Note: Solar water heaters are becoming more popular, and solar water heater expansion tanks are required too.

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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Expansion Tank Cost 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 in a spacious basement 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.
  • Where you Live – Local Cost of Living is a factor – Plumbing costs are higher in metro areas of the East Coast and the Pacific Northwest than in Midwest, South and other regions.

Expansion Tank and Installation Supplies Cost

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.

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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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.

Installation Labor Cost Range

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

Typical Installation Time for a Pro

  • 1-2 Hours | Time to Install a Water Heater Expansion Tank
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Are You a Plumber or Expansion Tank Installer?

If so, head over to our Costimates Pro’s page, and help us make this page better and more accurate for both our visitors and your future customers.

DIY or Hire a Pro?

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.

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Reviewed and edited by Steve Hansen of Costimates

steve hansen of costimates-sm Steve Hansen, that's me, the Senior Editor of Costimates. (Learn more about myself and our team) I'm an avid home improvement professional with more than 37 years experience working on all types of residential new home building, upfits, repairs and remodeling.

"Like most homeowners, I was frustrated with the lack of quality information available on specific home improvement repairs and renovations. In 2015, Costimates was formed to help homeowners learn as much as possible about various projects and their costs so they could make better financial decisions."