Sized to the Heater and House Pressure, Charged to Match, and Held Up Properly
5 picks compared · prices, ratings and stock checked October 12, 2026
Our Top Pick
For a typical 40 or 50 gallon tank heater, the Eastman 60022 2 Gallon Thermal Expansion Tank, with a stated 40 psi pre-charge, 150 psi and 210°F ratings and a 3/4 in MIP connection. For a bigger heater or higher house pressure, step up to the EFIELD 4.5 Gallon Water Heater Expansion Tank.
4.7 on Amazon · 699 ratings
Quick answer
If a check valve, backflow preventer or pressure-reducing valve on your main makes the plumbing a closed system, your water heater needs an expansion tank on its cold supply; for a typical 40 or 50 gallon heater at ordinary house pressure, makers' charts generally call for about a 2 gallon tank, such as the Eastman 60022 2 Gallon Thermal Expansion Tank, rated 4.7 stars across 699 Amazon ratings. Its listing states a 40 psi factory pre-charge and 150 psi and 210°F ratings. Before installing, read your static water pressure with a gauge and set the tank's air charge to match.
Every pick below is currently stocked — ratings and stock read from Amazon on 12 October 2026.
Best for: A standard 40 or 50 gallon tank water heater on a closed system at ordinary house pressure
Listing verified 13 Oct 2026
Best for: A heater larger than 50 gallons, a home with high water pressure, or a heater set hotter than usual
Listing verified 13 Oct 2026
Best for: A 2 gallon-class install where the tank hangs off a long pipe run or a wall, and needs support
Listing verified 13 Oct 2026
Best for: An under-sink point-of-use heater or a tankless setup on a closed system, where the heater's maker calls for expansion control
Listing verified 13 Oct 2026
Best for: A homeowner who wants the air-charge limits spelled out before setting the tank
Listing verified 13 Oct 2026
How this page was made: we compare the current Amazon listings, the makers' published specs and what verified buyers report, then rank by fit for the job. Ratings, review counts and stock are read from Amazon and dated. We earn a commission on purchases through our links; it does not change the order. Reviewed by Marcus Reed, IICRC-certified Water Restoration Technician.
Full Reviews
Each pick in detail: what the listing states, what buyers report, and where it falls short.
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Listing verified 13 Oct 2026
See it on Amazon ↗Best Overall
Quick Verdict
Eastman 60022 2 Gallon Thermal Expansion Tank: the fully specified 2 gallon tank for a typical heater, once its air charge is set to your pressure.
Key Specs
Capacity
2 gallons
Pre-charge (stated)
40 psi from the factory
Ratings (stated)
Up to 150 psi and 210°F
Connection
3/4 in MIP
Construction (stated)
Butyl rubber diaphragm; 304 stainless steel system connection
Warranty (stated)
6-year limited warranty
Pros
Cons
Suited to
A standard 40 or 50 gallon tank water heater on a closed system at ordinary house pressure
Our take
Eastman's listing gives the numbers that matter for a standard install: 2 gallons, a 40 psi factory pre-charge, ratings of 150 psi and 210°F, a butyl rubber diaphragm and a 304 stainless steel connection on a 3/4 in MIP thread. Treat the 40 psi as a starting point, not a setting. Many homes run higher, and a tank charged below house pressure fills partly with water as soon as it is connected, which uses up room meant for expansion and flexes the diaphragm harder. Read your static pressure with a gauge and add air to match before the tank goes in. Plan a strap or bracket too, since none comes in the box.
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Listing verified 13 Oct 2026
See it on Amazon ↗Best Larger Tank
Quick Verdict
EFIELD 4.5 Gallon Water Heater Expansion Tank: the step-up size for big heaters or high pressure, on a listing that leaves its ratings to the label.
Key Specs
Capacity
4.5 gallons
Connection
3/4 in MNPT
Water use (stated)
Certified for potable water
Model
TANK002; a 2.1 gallon version (TANK001) is sold separately
Pre-charge, pressure and temperature ratings
Not stated on the listing
Diaphragm material
Not stated on the listing
Pros
Cons
Suited to
A heater larger than 50 gallons, a home with high water pressure, or a heater set hotter than usual
Our take
A 4.5 gallon tank is the usual next size up, and three things push you toward it: a larger heater, higher house pressure, and a hotter tank setting, because each puts more water into the tank per heating cycle or leaves less room in the air cushion. EFIELD's listing confirms potable-water certification and a standard 3/4 in MNPT connection, but leaves out the factory pre-charge, the pressure and temperature ratings and the diaphragm material. Read those off the tank's label when it arrives, and set the pre-charge before installing. Full of water after a diaphragm failure, 4.5 gallons weighs more than 37 lb, so strap or bracket it.
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Listing verified 13 Oct 2026
See it on Amazon ↗Best With Mounting Bracket
Quick Verdict
Solimeta 2.1 Gallon Potable Water Expansion Tank: a 2 gallon-class tank that comes with the wall bracket most installs should have.
Key Specs
Capacity
2.1 gallons
Ratings (stated)
150 psig maximum pressure; 200°F maximum temperature
Connection
3/4 in MNPT, with a rubber thread protector
Construction (stated)
Butyl rubber diaphragm; 304 stainless steel fittings
Mounting (stated)
Adjustable wall mounting bracket set included
Pre-charge
Not stated on the listing
Pros
Cons
Suited to
A 2 gallon-class install where the tank hangs off a long pipe run or a wall, and needs support
Our take
The bracket is the reason to pick this tank. An expansion tank screwed onto a tee hangs its weight on that one joint, and if the diaphragm ever fails the tank fills with about 17 lb of water. Solimeta includes an adjustable wall bracket, so the wall carries the tank and the pipe only carries water. The listing states a 150 psig limit, a 200°F limit, a butyl rubber diaphragm and 304 stainless fittings, but not the factory pre-charge, so check it with a tire gauge and match it to your house pressure. Its bullets also mention boilers and hydronic heating; on a water heater, make sure the tank's label says potable.
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Listing verified 13 Oct 2026
See it on Amazon ↗Best for Point-of-Use and Tankless
Quick Verdict
Eastman 60008 Mini Thermal Expansion Tank: the right size for a small point-of-use or tankless heater, and the wrong one for a tank heater.
Key Specs
Suits (stated)
Tankless or point-of-use water heaters with a storage capacity of 2 gallons or less
Connection
1/2 in MIP
Body (stated)
304 stainless steel; indoor or outdoor installation
Ratings (stated)
Max 150 psi; max 210°F
Mounting (stated)
Any orientation
Pressure (stated)
Adjustable; factory pre-charge not stated
Pros
Cons
Suited to
An under-sink point-of-use heater or a tankless setup on a closed system, where the heater's maker calls for expansion control
Our take
Read this listing carefully, because the 2-gallon in its title describes the heater, not the tank. Eastman sells the 60008 as a mini tank for tankless or point-of-use heaters that store 2 gallons or less, and it is far too small for a 40 or 50 gallon heater. On a small heater it makes sense: a closed system still pushes pressure up when that water heats, and a compact stainless tank that mounts in any orientation fits under a sink where a full-size tank would not. It has a 1/2 in MIP connection and ratings of 150 psi and 210°F. Check the heater's manual first, since not every tankless maker calls for one.
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Listing verified 13 Oct 2026
See it on Amazon ↗Clearest Air-Charge Limits
Quick Verdict
GE Appliances 2.1 Gallon Water Heater Expansion Tank: a 2 gallon-class tank with its 40 psi pre-charge and 80 psi charge ceiling stated plainly.
Key Specs
Capacity
2.1 gallons
Pre-charge (stated)
40 psi from the factory
Maximum charge (stated)
80 psi
Temperature (stated)
Up to 200°F
Connection
3/4 in MNPT
Diaphragm and working pressure rating
Not stated on the listing
Pros
Cons
Suited to
A homeowner who wants the air-charge limits spelled out before setting the tank
Our take
GE's listing is the clearest here on air charge: 40 psi from the factory, with a stated maximum charge of 80 psi. That ceiling is useful. If your static water pressure reads above 80 psi, you cannot charge this tank to match it, and that pressure is a problem in its own right, because many US plumbing codes call for a pressure-reducing valve once static pressure passes 80 psi. In that house, fit the PRV first, then charge the tank to the PRV's outlet setting. Beyond that, the listing gives a 200°F limit and a 3/4 in MNPT connection, but no diaphragm material or working pressure rating, so check the label.
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What to know before you buy.
Water takes up more room when it is heated. Warming it from about 50°F at the cold main to 120°F grows its volume by roughly 1 percent, so a 50 gallon heater has about half a gallon of extra water to put somewhere each time it heats a full tank. In an open system, that water is pushed back out toward the street main and nobody notices. A check valve, backflow preventer or pressure-reducing valve (PRV) on the main closes the system. Water barely compresses, so house pressure climbs instead until something gives, usually the temperature and pressure (T&P) relief valve on the heater. Model codes such as the International Plumbing Code call for thermal expansion control on a closed system, and your local code decides the details. An expansion tank gives that half gallon a cushion of air to push into.
Three things set the size: the heater's gallons, the water temperature, and the house pressure. More gallons and a hotter setting mean more expansion. Higher pressure matters in a less obvious way. The tank's air is charged to match house pressure, so at high pressure the cushion starts out already squeezed and has less room left to take water before pressure climbs. That is why makers publish sizing charts by heater size and supply pressure. On typical charts, a 2 gallon tank covers a 40 or 50 gallon heater at moderate pressure, and the chart moves you to a larger tank, often around 4.5 gallons, for a bigger heater or higher pressure. Use the chart for the exact tank you buy. None of the 2 gallon-class listings on this page prints its own chart.
This is the step most installs skip. Every tank has an air valve like a tire valve, and the air behind the diaphragm should match your home's static water pressure, the reading with no water running anywhere. Measure it with a pressure gauge on a hose bib or the heater's drain valve. If you have a PRV, use the pressure it delivers. Then check the tank with a tire gauge before it is connected, while it holds no water, and add air with a bicycle pump or compressor, or let some out, until it matches. Eastman and GE ship at 40 psi, which is lower than many homes run. Never charge past the tank's stated limit; GE gives 80 psi as its maximum. If a tank is already in place, shut off the water and relieve the pressure before checking it.
The tank goes on the cold water supply to the heater, downstream of the check valve, backflow preventer or PRV that closes the system, so it sits between that valve and the heater. Use a tank sold for potable water; tanks made only for boiler and hydronic heating loops are not meant for drinking water. Then think about weight. Water weighs about 8.3 lb per gallon, so if the diaphragm fails, a 2 gallon tank fills with about 17 lb of water and a 4.5 gallon tank with more than 37 lb, all hanging on one threaded joint. Support it with a bracket, strap or shelf; Solimeta includes a wall bracket. Follow the maker's instructions on orientation. Eastman says its 60008 mini mounts any way, but the other listings here do not address it.
A working tank is mostly air. Tap it with your knuckles: the top should sound hollow, and a dull thud all the way up suggests it has filled with water. Press the air valve stem briefly; water instead of air means the diaphragm has failed and the tank needs replacing. A pressure gauge with a red max needle, left on a hose bib overnight, shows the spikes a dead tank no longer absorbs. The classic symptom is a T&P relief valve that dribbles after the heater runs, since that valve is usually set to open at 150 psi or 210°F. Never cap or plug a T&P valve. EPA WaterSense notes that a faucet dripping once per second wastes more than 3,000 gallons a year, and a relief valve that drips every cycle is wasting water and warning you.
You may not need a tank at all if your home has an open system, with no check valve, backflow preventer or PRV on the main, though some heater makers and local codes call for expansion control anyway, so check the heater's manual. A tankless heater stores little water, and many need no tank; a mini tank like the Eastman 60008 is for small heaters whose makers call for one. If static pressure reads above 80 psi, fix that first with a PRV; a tank alone cannot fix high pressure. Call a licensed plumber for soldered connections, work on a gas heater, any job your area requires a permit for, or a T&P valve that keeps dripping with a charged tank in place. If a leak has already soaked the floor, EPA advises drying it within 24 to 48 hours to prevent mold growth.
You need one if your plumbing is a closed system, meaning a check valve, backflow preventer or pressure-reducing valve on the main stops heated water from pushing back into the street supply.
Many water utilities and local codes require one in that case. Look for a valve where the main enters the house, and check the heater's manual. A T&P valve that drips after the heater runs is a common sign the system is closed.
Usually about 2 gallons at moderate house pressure, but the maker's sizing chart for your exact tank decides. Charts size by heater gallons and supply pressure, because higher pressure leaves the air cushion less room.
At high pressure, or with a hot tank setting, the chart may move you up to a larger tank of around 4.5 gallons, such as the EFIELD 4.5 Gallon. Measure your static pressure before you choose.
The air charge should match your home's static water pressure, measured with no water running, or the outlet setting of your PRV if you have one. Tanks often ship at 40 psi, as Eastman's and GE's listings state, so most need air added.
Set it with a tire gauge and bicycle pump before connecting the tank, and stay within the tank's limit, such as the 80 psi maximum charge GE states.
On the cold water supply line to the heater, between the heater and the check valve, backflow preventer or PRV that makes the system closed. Model codes such as the International Plumbing Code place it downstream of those valves.
Close to the heater is common and easy to service. Support the tank with a bracket or strap rather than letting it hang from the pipe joint.
Tap it and press its air valve: a hollow sound near the top is good, while a solid sound throughout or water from the valve means the diaphragm has failed.
Other signs are a T&P valve that drips after the heater runs and pressure spikes shown on a gauge with a red max needle left on a hose bib overnight. A failed tank should be replaced, not recharged.
SometimesDepending on the maker.
Eastman says its 60008 mini tank can be mounted in any orientation, but the other listings on this page do not say, so follow the installation sheet that comes with your tank. Whatever the angle, support the tank with a bracket or strap, because a sideways tank puts even more bending load on the threaded joint.
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