Table of Contents

10 sections 11 min read
Garrett FitzgeraldBy Garrett Fitzgerald

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An expansion tank absorbs extra pressure when heated water expands in a closed system. The listings below describe that job for water heaters, boilers and hydronic loops, so each tank needs to match the heater or loop it serves.

Most of these listings are written for standard water heaters or boilers, not solar-specific loops. Only the oiununo listing names solar thermal. Use the capacity, pressure and temperature data below as a starting point, then confirm ratings with your installer and the maker. For how tanks fit into a layout, see Solar Water Heater Storage Tanks: What Homeowners Should Know.

Every specification on this page comes from each product’s Amazon listing, checked on 7 November 2026. We have not used these products ourselves, so the picks are based on published specifications only.

For the wider parts list, read Solar Water Heater Components: Collectors, Tanks, Pumps and Pipes.

Quick picks

How we chose these

  • Capacity and heater size match the tank volume to the water heater or loop it serves.
  • Pressure and temperature ratings as stated by the maker, and whether a rating is given at all.
  • Mount and connection such as 3/4-inch MNPT versus 1/2-inch fittings, and wall, floor or ceiling mounting.
  • Water contact and materials such as butyl diaphragms, stainless fittings and potable-use claims.

Several listings leave pressure or temperature unstated, so check the maker’s manual before you buy.

Comparison table

Product Capacity Max pressure Max temperature Best for
1. EFIELD TANK001 2.1 gallons Not stated Not stated Standard floor-mount installs
2. Solimeta S23012 2.1 gallons 150 PSIG 200°F Wall mounting with bracket
3. TTFLEX 4.5 gallon 4.5 gallons Not stated Not stated Larger water heater lines
4. GE PM77X001 2.1 gallons Not stated (40 PSI pre-charge) 200°F Pre-charged residential heaters
5. PEVEPEXE 4.5 gallon 4.5 gallons 150 PSI Not stated Heaters up to 100 or 130 gallons
6. VEVOR 4.4 gallon 4.4 gallons Not stated (29 PSI pre-charge) Not stated Systems not used for drinking water
7. Amtrol ST-5 2 gallons 150 psi 200°F Wall or ceiling mounting
8. WaterWorker G5L 2 gallons Not stated (25 psi pre-charge) Not stated NSF 62 listed for potable use
9. HPS EASYFLEX 4.5 gallons Not stated Not stated Stainless fittings and wall kit
10. Seelink TANK001-1 2.1 gallons Not stated Not stated Tight installation spaces
11. ProWaterParts 1ET2G12F 2 gallons 130 PSI Not stated Wall-bracket installs
12. PLUMBINGMASTER 2.1 gallon 2.1 gallons Not stated Not stated Residential closed-loop systems
13. Eastman 60022 2 gallons 150 psi 210°F 30 to 50 gallon heaters
14. PEVEPEXE 2.1 gallon 2.1 gallons 150 PSI Not stated Heaters up to 50 or 60 gallons
15. oiununo 2.1 gallon 2.1 gallons 150 PSI operating (207 PSI rated) Not stated Solar thermal named in listing
16. Amtrol SX-40V 20 gallons 100 psi Not stated Large hydronic systems
17. Amtrol 30 Extrol 4.4 gallons 100 psig Not stated Boiler systems
18. Eastman 60008 2 gallons 150 psi 210°F Tankless and point-of-use

Not stated means the Amazon listing gives no value for that spec. Pressure figures are as stated by each maker and may differ in meaning, such as pre-charge versus working pressure.

Water heater expansion tanks

Tanks listed for standard residential water heaters, from about 2 to 4.5 gallons.

1. EFIELD TANK001: for standard floor-mount water heater installs

EFIELD says the tank soaks up extra thermal pressure to protect the water heater and plumbing. The listing gives a standard 3/4-inch MNPT connection and a floor mount.

  • Weight listed at 5 pounds (EFIELD)
  • Listing says it is certified for potable water use (EFIELD)

2. Solimeta S23012: for wall-mounted water heater or hydronic installs

Solimeta lists this tank for water heaters, boilers and hydronic heating, with a wall bracket set included. Its listing describes a diaphragm made of butyl and fittings in 304 stainless steel.

  • Listed size 9 inches wide by 16 inches high (Solimeta)
  • Weight listed at 5 pounds (Solimeta)

3. TTFLEX 4.5 Gallon Expansion Tank: for larger water heater lines

TTFLEX calls this an inline tank whose plastic liner keeps the water side separate from the air precharge, with a butyl diaphragm. It says the paint finish resists rust.

  • Listing says the tank takes in expanded water and sends it back once hot water is drawn (TTFLEX)
  • Capacity stated as 4.5 gallons (TTFLEX)

4. GE Appliances PM77X001: for pre-charged residential water heaters

GE Appliances says the tank absorbs extra pressure from heated water and comes factory pre-charged to 40 PSI. The listing gives a 200°F max temperature and a standard 3/4-inch MNPT fitting.

  • Carbon steel material listed (GE Appliances)
  • Maximum charge listed at 80 PSI (GE Appliances)

5. PEVEPEXE 4.5 Gallon Accumulator: for heaters up to 100 or 130 gallons and combi-boilers

PEVEPEXE says this 4.5-gallon tank fits residential heaters up to 100 or 130 gallons and also suits combi-boilers and hydronic systems. It lists a 150 PSI max pressure and a 40 PSI pre-charge.

  • Listed as meeting EPA and Prop 65 standards (PEVEPEXE)
  • Item weight listed at 5.8 pounds (PEVEPEXE)

6. VEVOR Expansion Tank 4.4 Gallon: for hot water systems not used for drinking water

VEVOR describes a thickened carbon steel tank pre-charged to 29 PSI for hot water systems, with a 3/4-inch NPT connection. The listing says it is not for drinking water and should not connect to the public supply.

  • Dimensions 10.94 by 10.94 by 14.57 inches (VEVOR)
  • Thickened carbon steel body (VEVOR)

7. Amtrol ST-5: for indoor wall or ceiling mounting

Amtrol lists this 2-gallon tank for wall or ceiling mounting, with energy-efficient and safety-enhancing features in its listing. The listing gives 150 psi and 200°F maximums.

  • Dimensions 8 inches wide by 12.63 inches high (Amtrol)
  • Weight listed at 5 pounds (Amtrol)

8. WaterWorker G5L: for potable water systems that need an NSF 62 listing

WaterWorker says the tank meets NSF standard 62 and uses a butyl diaphragm with a polypropylene liner, which it says adds no taste or odor. The listing also states a 5-year warranty.

  • Deep drawn steel dome said to be twice as strong as rolled steel at equal thickness (WaterWorker)
  • Listing says tanks can be combined for larger volume (WaterWorker)

9. HPS EASYFLEX 4.5 Gallon: for water heaters that need stainless fittings and a wall kit

HPS describes a cold-rolled steel body, a 3/4-inch stainless MIP connection, and a diaphragm that is all butyl, with a polypropylene liner. It says an optional wall bracket kit is available.

  • Listing says made in South Korea (HPS)
  • Offered in 2.1-gallon and 4.5-gallon sizes (HPS)

10. Seelink TANK001-1: for tight installs under sinks or in closets

Seelink describes a 2.1-gallon tank with a flexible butyl diaphragm and a rust-resistant 304 stainless fitting. The listing says it is compact enough for spaces such as under sinks and needs no special tools to install.

  • Dimensions 8 inches wide by 12.75 inches high (Seelink)
  • No electric power source listed (Seelink)

11. ProWaterParts 1ET2G12F: for wall-mounted residential water heater tanks

ProWaterParts lists a 2-gallon accumulator with a 1/2-inch female NPT connection and wall brackets included. The listing gives 130 PSI max liquid pressure and 30 PSI pre-pressurized air.

  • Dimensions 12 by 9 by 7 inches (ProWaterParts)
  • Weight listed at 5.3 pounds (ProWaterParts)

12. PLUMBINGMASTER 2.1 Gallon: for residential closed-loop systems

PLUMBINGMASTER says the 2.1-gallon tank handles thermal expansion in closed-loop systems and has a standard 3/4-inch MNPT connection. It describes an appliance-grade paint finish for rust resistance.

  • Described as sized for residential systems (PLUMBINGMASTER)

13. Eastman 60022 Thermal Expansion Tank: for 30 to 50 gallon water heaters and boilers

Eastman says this 2-gallon tank is made in the USA for water heaters and boilers from 30 to 50 gallons. It lists a butyl diaphragm and fittings in 304 stainless.

  • Max pressure 150 psi and max temperature 210°F (Eastman)
  • Dimensions 8.3 inches wide by 12.4 inches high (Eastman)

14. PEVEPEXE 2.1 Gallon: for heaters up to 50 or 60 gallons

PEVEPEXE says this 2.1-gallon tank fits residential heaters up to 50 or 60 gallons and also suits combi-boilers and hydronic systems. It lists a 150 PSI max pressure and a 40 PSI pre-charge.

  • Listed as meeting EPA and Prop 65 standards (PEVEPEXE)
  • Seamless TPV liner and butyl diaphragm described (PEVEPEXE)

15. oiununo Potable Thermal Expansion Tank 2.1 Gallon: for potable systems where the listing names solar thermal

oiununo lists a 2.1-gallon potable tank with a 3/4-inch MNPT connection and food-grade 304 stainless steel. The listing names solar thermal among its uses and gives a factory rating of 207 PSI, with operating pressure kept at or below 150 PSI.

  • Listing names solar thermal and residential plumbing as uses (oiununo)
  • Dual O-ring air valve described (oiununo)

Larger and hydronic tanks

Bigger tanks and boiler-style units listed for hydronic or large system use.

16. Amtrol SX-40V Extrol: for large hydronic systems

Amtrol describes a vertical 20-gallon hydronic tank with a thick butyl and EPDM diaphragm and a strong steel shell. The listing gives a 100 psi maximum pressure.

  • Depth listed at 32 inches (Amtrol)
  • Listed as a vertical stand style (Amtrol)

17. Amtrol 30 Extrol Boiler System: for boiler system expansion

Amtrol lists this 4.4-gallon boiler expansion tank with a 2.5-gallon maximum acceptance and a 100 psig maximum working pressure. It uses a 1/2-inch NPT connection.

  • Dimensions 11 inches diameter by 15 inches height (Amtrol)
  • Item weight listed at 1 pound (Amtrol)

Tankless and point-of-use

Small tanks listed for tankless heaters or point-of-use units with 2 gallons or less.

18. Eastman 60008 Mini Thermal Expansion Tank: for tankless or point-of-use heaters

Eastman describes a 2-gallon mini expansion tank for tankless or point-of-use heaters with 2 gallons or less of volume. The listing gives 150 psi and 210°F maximums and a 1/2-inch MIP connection.

  • Built with 304 stainless steel (Eastman)
  • Listing says it can be mounted in any orientation (Eastman)

Which one fits you

Your situation Look at Why
Standard water heater of 30 to 50 gallons Eastman 60022 or PEVEPEXE 2.1 gallon Eastman lists 30 to 50 gallon units; PEVEPEXE lists heaters up to 50 or 60 gallons
Tankless or point-of-use heater Eastman 60008 Listing limits use to heaters with 2 gallons or less of volume
Hydronic loop or boiler Amtrol SX-40V or Amtrol 30 Extrol Both list a 100 psi or 100 psig max working pressure
Solar thermal connection oiununo 2.1 gallon Only this listing names solar thermal; confirm the rating with your installer

Practical tips

  • Match the tank to the heater size the listing names, such as 30 to 50 gallons or 50 to 60 gallons, before you compare other specs.
  • Check that the maximum pressure and temperature meet your system’s needs, since several listings leave one or both unstated. Ask the maker for the rating in writing.
  • Look for butyl diaphragms and stainless fittings when they are listed, and confirm any potable-water certification if the tank will supply drinking water. See the Solar Water Heater Buying Guide for certifications and specs.

FAQ

Do these tanks all work with solar water heating?

Most listings describe water heater or hydronic use. Only the oiununo listing names solar thermal. Confirm the rating for your loop with your installer.

Why does the pre-charge matter?

Several listings give a pre-charge, such as 40 PSI from GE Appliances and PEVEPEXE or 25 psi from WaterWorker. WaterWorker says to set the charge as its manual describes.

Can I use a tank that is not for drinking water?

VEVOR says its 4.4-gallon tank is not for drinking water use and should not connect to the public water supply.

Sources

Specifications from each product’s Amazon listing, checked 7 November 2026: EFIELD TANK001, Solimeta S23012, TTFLEX 4.5 Gallon Expansion Tank, GE Appliances PM77X001, PEVEPEXE 4.5 Gallon Accumulator, VEVOR Expansion Tank 4.4 Gallon, Amtrol ST-5, WaterWorker G5L, HPS EASYFLEX 4.5 Gallon, Seelink TANK001-1, ProWaterParts 1ET2G12F, PLUMBINGMASTER 2.1 Gallon, Eastman 60022 Thermal Expansion Tank, PEVEPEXE 2.1 Gallon, oiununo Potable Thermal Expansion Tank 2.1 Gallon, Amtrol SX-40V Extrol, Amtrol 30 Extrol Boiler System, Eastman 60008 Mini Thermal Expansion Tank. Makers can change specifications; check the product page before you buy.

Garrett Fitzgerald

About Garrett Fitzgerald

Garrett writes about solar water systems. Each guide starts with research into how products are built and what owners report after months of use, and is revised when better options appear.