Water Heater Expansion Tank: Do You Need One? (T&P Dripping?)

If your T&P relief valve drips after the heater runs, your toilet fill valves keep failing, or an inspector flagged your new water heater install, thermal expansion may be the cause. The usual fix is a small potable-rated tank on the cold supply line.

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What thermal expansion actually is

Water expands when you heat it. Amtrol’s reference guide says the water in a 40-gallon heater expands to about 40.60 gallons when it reaches the set temperature. Water doesn’t compress, so that extra volume has to go somewhere.

In an open system it simply pushes back into the city main. That’s why older homes often never needed an expansion tank.

In a closed system it can’t. Many homes are closed systems, often without the owner knowing, because of a check valve, backflow preventer, or pressure-reducing valve (PRV) at the meter. Amtrol also lists water meters with check valves, and Rheem’s manual says a check valve can be part of a PRV, a water meter or a water softener. Once that one-way device is in place, the expanding water is trapped and the pressure rises every heating cycle.

What that pressure does

• The T&P valve weeps after the heater fires. People replace the valve and it drips again. Rheem’s manual says replacing the relief valve will not correct the problem, and A. O. Smith says the valve is not intended for the constant relief of thermal expansion.
• Fixtures and appliances take the pressure. A. O. Smith lists leaking faucets and damage to heater connections and to the pumps in washers and dishwashers. Its brochure says excess pressure can make rubber parts fail early, including flush valves.
• The heater takes it too. A. O. Smith says thermal expansion can cause premature tank failure and that its limited warranty does not cover that. Its brochure warns that extreme pressure can collapse the flue tube of a gas heater. Bradford White says its warranty does not cover thermal expansion damage such as pressure bulges.

A T&P valve that drips is a symptom to diagnose, never something to cap or plug. It is the tank’s last line of safety. Watts says never to plug a safety relief valve, and A. O. Smith says plugging the opening can cause property damage, serious injury or death. If the valve itself has failed, our T&P valve replacement guide matches the size, pressure and shank.

What the plumbing codes say about expansion tanks

Three model codes cover this. The wording below is the 2021 edition of each, as published. Which edition your city uses, and any local changes, are for your building department.

• IPC 2021, §607.3. Where a storage water heater is supplied with cold water that passes through a check valve, pressure reducing valve or backflow preventer, a thermal expansion control device must be connected to the heater’s cold supply pipe downstream of all of them. Thermal expansion tanks must be sized per the tank maker’s instructions so that system pressure stays within §604.8.
• IPC 2021, §504.4. The relief valve “shall not be used as a means of controlling thermal expansion.” Under §504.5, T&P valves are set at not more than 210°F and at a pressure not above the manufacturer’s rated working pressure or 150 psi, whichever is less.
• UPC 2021, §608.3. A water system with a check valve, backflow preventer or other normally closed device that stops pressure from dissipating back into the water main “shall be provided with an approved, listed, and adequately sized expansion tank or other approved device,” whatever type of water heater is used. It goes on the building side of that device and is sized and installed per the maker’s instructions. Pre-pressurized tanks must comply with IAPMO Z1088, and §608.2 says expansion tanks in drinking-water systems shall comply with NSF 61.
• IRC 2021, §P2903.4. A means of controlling pressure from thermal expansion must be installed where §P2903.4.1 or §P2903.4.2 requires it. That covers a PRV (service up to 2 inches) when thermal expansion pushes the downstream pressure above the PRV setting, and any backflow prevention device, check valve or other device on a system with storage water heating equipment that lets thermal expansion raise the pressure.

The IPC and IRC say “device,” and the UPC says “expansion tank or other approved device.” A tank is the usual answer.

Heater makers say it too. A. O. Smith’s manual says a properly sized and charged thermal expansion tank must be installed on all closed systems. Bradford White’s says not to run the heater in a closed system without proper provisions, meaning a tank and/or other device, and that its warranty does not cover thermal expansion damage. Rheem’s suggests a tank on the cold line between the heater and the check valve. Read the closed-system section of your own manual, because a skipped tank can affect your warranty.

Georgia. Since January 1, 2026, Georgia’s state minimum plumbing code has been the 2024 IPC with Georgia amendments. It keeps the §504.4 sentence quoted above. Its amended §607.3 puts the thermal expansion control device downstream of all check valves, pressure reducing valves, backflow preventers and shut-off valves, and says thermal expansion tanks shall be located a minimum of 18 inches in developed length from the water heater’s cold-water inlet fitting. Georgia’s older 2018 text also required an expansion control device when the relief valve discharge piping ran upward; the 2026 amendments rewrote §504.6 without that sentence.

Separately, IPC §604.8 requires a PRV where static pressure in the building is over 80 psi, reducing it to not more than 80 psi. That is the quiet irony of this subject: Amtrol lists PRVs among the one-way devices that trap expanding water, so the valve the code requires is often what creates the need for the tank. (Replacing the PRV itself? Our PRV replacement guide matches the models by brand.)

Find out whether your system is closed — without opening anything

You do not need to identify the device at the meter. You can watch the symptom instead, and it takes one gauge and one afternoon. This is our field check, not a maker procedure.

1. Screw a pressure gauge onto a hose bibb and open it fully. Use one on the house side of the PRV: IPC §604.8 exempts lines to outdoor faucets from the PRV rule, so some hose bibbs read street pressure and will not show the rise. A. O. Smith puts its gauge between the PRV and the expansion tank. Note the reading with no water running. That is your static pressure.
2. Run a good volume of hot water — a full tub, or a long shower — so the heater has to reheat a substantial charge of cold.
3. Close everything and leave the gauge alone while the heater recovers.
4. Read it again. On an open system the pressure comes back to roughly where it started. On a closed system it climbs and stays climbed, because there is nowhere for the extra volume to go. A gauge with a peak-recording hand left on overnight catches the highest spike of the day, which is usually the one doing the damage.

Take the first reading when the heater has not just fired. A. O. Smith warns that a pressure read while the water is already hot and expanded gives a false number. Its fix is to run a hot faucet for 15 minutes, shut it off and read the pressure right away.

If the static reading alone is over 80 psi, you have a second problem to solve before the expansion tank means much; the pressure guide covers the range and water pressure gauges covers the tool.

How to size a water heater expansion tank

Sizing takes three inputs: the heater’s size in gallons, the house supply pressure and the thermostat setting. Then read the tank maker’s own chart. The makers’ charts rest on different assumptions, so do not mix rows between them.

Use the right pressure number. A. O. Smith’s guide defines the pressure in its chart as the highest recorded inlet pressure in a 24-hour period, which is what a 24-hour max pointer gauge test records. Amtrol adds that you should not set the water heater temperature higher than the expansion tank maximum.

Amtrol Therm-X-Trol, thermostat set no higher than 140°F (Amtrol labels it “Maximum Temperature Setting 140°F”). Tank volume in gallons, by heater size and supply pressure.

Amtrol, thermostat set no higher than 160°F. A hotter setting moves several rows up.

Amtrol says its chart assumes 40°F incoming water, a 150 psi T&P valve and a precharge equal to the static supply pressure. Its 180°F chart is on the same sheet. Amtrol’s model names for these volumes are ST-5 (2.0 gallons), ST-12 (4.4) and ST-25V (10.3); the 3.2-gallon size is the ST-8 (our reading of Amtrol’s two charts). One conflict: Amtrol’s older 2010 reference guide listed the ST-5 (2.0 gallons) for a 60-gallon heater at 140°F and 40 or 60 psi, and its 2017 sheet lists 3.2 gallons. We follow the newer sheet.

A. O. Smith (owner’s manual chart, thermostat assumed 140°F): at 40, 50 and 60 psi, heaters of 30 to 66 gallons take its 2-gallon tank (2.1 gallons) and heaters of 80 to 120 gallons take its 5-gallon tank (4.5 gallons). Its 70 and 80 psi rows are inconsistent. The manual’s 80 psi row calls for 5 gallons on a 40-gallon heater but 2 gallons on a 50-gallon one, and the brochure’s rows differ from the manual’s there. A. O. Smith recommends 60 psi or less and says a PRV is required above 80 psi.

Zilmet (quick chart for its Easy Pro tanks, thermostat up to 150°F): a 40 or 50 gallon heater takes the ZEP5 at 40, 60 or 80 psi, and a 60 or 80 gallon heater takes the ZEP12. If you are unsure, Zilmet says to go to the next larger size, because you can never oversize an expansion tank but can easily undersize one.

Watts gives an acceptance-volume table by precharge for its PLT tanks, not a heater-size chart. It is in the PLT-12 entry below.

Example. A 50-gallon heater on 60 psi with the thermostat at 140°F: Amtrol says 2.0 gallons, A. O. Smith says 2 gallons and Zilmet says the ZEP5. Change two inputs to an 80-gallon heater on 80 psi and Amtrol says 4.4 gallons, A. O. Smith says 5 gallons and Zilmet says the ZEP12.

Set the precharge to your supply pressure

Sizing fixes the tank. The air charge decides whether it works. Amtrol says the precharge must match the incoming supply pressure and that doing it wrong can contribute to premature tank failure. Its guide shows why: with a 40 psi precharge on 70 psi supply, the supply pressure pushes the diaphragm in and takes up space before the water has even started to expand. Here is each maker’s rule:

• Amtrol: with the tank empty of water, adjust the air precharge to match the cold water supply pressure. Amtrol ships at 40 psi.
• Watts: read the system pressure first (open a faucet so the pressure equalizes, close it, read the gauge), then set the tank to that number before you install it. Adjust only under zero system pressure. The normal factory precharge is 20 psi, and Watts says never to exceed an 80 psi air charge. If system pressure is over 80 psi, Watts says to add a PRV or put the tank on a riser below 80 psi.
• A. O. Smith: ships at 38 psi. If inlet pressure is higher, match the air pressure to it, but not above 80 psi. A. O. Smith’s check is to shut the main, open a faucet until the flow stops, then read the tank with a tire gauge. Raise it with a manual tire pump. Lower it by pressing the valve core.
• Zilmet: measure and adjust the precharge, if necessary, so it equals the operating pressure of the system, and only when the tank is empty of water and open to atmosphere.

The wording differs, but all four mean the same thing: no system pressure on the water side when you read or set the air. Put the cap back on tight. Amtrol warns that a valve cap that is not properly sealed will lose precharge and the tank will fail.

Best water heater expansion tanks

Three tanks, all sold as potable-water tanks. The specs below come from the maker documents named in each entry, not from our own testing.

Top pick for 40 to 50 gallon heaters: Amtrol Therm-X-Trol ST-5. Amtrol’s installation sheet covers the ST-5 for residential potable water, and its sizing guide says the ST-5 through ST-210V are listed by NSF 61. Amtrol lists it at 2.0 gallons with a 0.9 gallon maximum acceptance, 8 inches across and 12 5/8 inches tall, 5 pounds, with a 3/4-inch NPT connection. It carries a five-year limited warranty and an InSight cap that changes color when the tank should be replaced. Amtrol says to press the Turbulator into the tee connector before you install the tank. Watch for this: 2.0 gallons fits the 40 and 50 gallon rows of the 140°F chart at 40 to 80 psi. At a 160°F setting it still fits a 40-gallon heater up to 60 psi and a 50-gallon heater at 40 psi; past that, Amtrol’s chart moves to 3.2 gallons. See the Amtrol ST-5 on Amazon.

For bigger heaters: Watts PLT-12. Watts lists it at 4.5 gallons, 150 psi and 200°F, with a 3/4-inch male connection, 10.5 inches across, 13.5 inches long and 10 pounds. Its instruction sheet says it is certified to ANSI/NSF 61 and listed by IAPMO. It ships with a 20 psi precharge, so raise it to your supply pressure. Watts’ acceptance table shows how a higher precharge shrinks the room for water: 2.88 gallons at a 40 psi precharge, 2.49 at 60 and 1.85 at 80. Watts prefers vertical mounting and allows horizontal if the tank is properly supported. It carries a one-year limited warranty. At 140°F and 40 to 60 psi, Amtrol’s chart lists 3.2 to 4.4 gallons for 60 to 120 gallon heaters and A. O. Smith’s lists 5 gallons for 80 to 120, so the 4.5-gallon PLT-12 sits in that range (our reading; Watts prints no heater-size chart). The Amazon buying link is currently removed; see the seller note below.

Another 2-gallon option: Thrifco 4906032. Thrifco’s product page lists 2 gallons, a 3/4-inch stainless MIP connection, a butyl diaphragm, a 150 psi maximum, 200°F operating temperature, a 40 psi factory precharge and a polypropylene liner, and says “UPC certified/ NSF 61 compliant.” That is the maker’s wording, so ask for the certification listing if your inspector wants proof. The page has no installation sheet or sizing chart, so size it from the charts above. See the Thrifco 4906032 on Amazon.

Seller check, October 6, 2026. The Amtrol ST-5 and Thrifco 4906032 listings were in stock from third-party sellers NYDIRECT and Jenco Wholesale, Inc., respectively. The Watts PLT-12 listing showed Big Frog Supply with only four left, so we removed its buying links. Sellers and stock change; check the current seller before ordering.

🔴 Buy a tank listed for potable water. Hydronic (heating loop) tanks are a different product. Zilmet’s manual says its hydronic tanks “cannot be used for the production of potable (drinking) water” and have no internal liner, so the water touches the steel dome. A. O. Smith labels its boiler tank line not for use with potable water heating systems. Look for the word potable and NSF 61 on the listing or the maker’s sheet.

Installing a water heater expansion tank

Amtrol says a qualified professional must install its tanks, and Zilmet says only qualified and licensed personnel may. Rules on who may do the work vary by place, so check yours before you start. This is the order the makers’ sheets follow.

1. Set the precharge first, as above, with the tank empty of water.
2. Shut off the water and the heater. Close the heater’s cold supply or the main, then the electricity or gas. Watts says to drain the system following the heater maker’s instructions before you cut the tank in. Zilmet says the system must be shut off, cooled and not pressurized.
3. Put it on the cold supply, on the heater side of the one-way device. Amtrol and Rheem both say the cold line between the heater and the check valve, PRV or backflow preventer. A. O. Smith lists the order on the cold line, starting at the heater, as the tank (at least 18 inches from the heater’s cold inlet fitting), a pressure gauge, then the PRV if you have one. Georgia’s current code also puts it downstream of the shut-off valve and at least 18 inches in developed length from the cold inlet.
4. Mount and support it as the maker says (table below).
5. Turn the water on and purge the air. Open a hot faucet until the air is out of the system (Watts, Amtrol and A. O. Smith all say this), then check the connections for leaks. Turn the power or gas back on only after that. Watts restores power after the purge, and Bradford White warns that an electric heater’s elements can fail if they are not fully under water. Amtrol says to open a hot faucet briefly while the heater comes up to temperature so the first expansion can bleed off. Watts says to recheck the system pressure afterward.

The makers do not all agree. Amtrol’s older 2011 technical bulletin said its tank can be mounted in any position, and its 2017 installation sheet says vertical, hanging down. Follow the sheet packed with your tank.

• The T&P valve stays. Amtrol says a relief valve must be installed, and that a licensed contractor should inspect the T&P valve at least every 3 years or if it has discharged. A. O. Smith says to lift the T&P lever at least once a year with the outlet clear, because the water may be extremely hot. Never plug it.
• Put the tank where a leak will not do damage. Watts and A. O. Smith both say an expansion tank, its piping and its connections may eventually leak, and that you should not install one without adequate drainage provisions.
• Keep it from freezing. A. O. Smith says to locate the tank indoors in an area not subject to freezing, and Amtrol says not to expose its tanks to freezing temperatures.
• Check it on a schedule. Amtrol says a professional plumber should check the system, tank included, yearly and more often as it ages. Zilmet says to check the precharge and inspect the tank every six months. Amtrol says to replace a corroded or damaged tank and not to adjust its precharge.

Four ways a correctly bought tank still does nothing

Each of these can leave a tank on the wall that looks installed:

• Precharge left at the factory number. Amtrol ships at 40 psi, A. O. Smith at 38 psi and Watts at 20 psi. On a 70 psi house, Amtrol’s own guide shows the supply pressure pushing the diaphragm in before the water even heats.
• Precharge read or set with the system live. Put a tire gauge on the air valve of an installed, pressurized tank and the number does not mean what you think. Amtrol says to check it only while the tank is isolated and empty of water, and Watts says only under zero system pressure. A reading taken any other way can pass a bad tank.
• Fitted in the wrong place. The makers and the codes put it on the cold supply, downstream of the check valve, PRV or backflow preventer. Upstream of that device the tank is on the open side of the system, where the expansion was never trapped. On the hot outlet, Amtrol says the expanded water sits in the tank and cools, so hot water is not immediately available at the fixtures.
• Never rechecked. Amtrol and Zilmet both set a schedule (yearly and every six months). A. O. Smith lists a mismatched air charge as one cause of a weeping T&P valve, so a valve that starts weeping after quiet years is a reason to check the tank.

When it is not the expansion tank

Arguing the other side honestly: a dripping T&P valve is not always thermal expansion.

• A worn or clogged valve. A. O. Smith lists wear and lime or calcium buildup as a cause. It says that if the valve does not fully reset after you lift the lever and keeps releasing water, you should close the cold supply and replace it. If the system tests as open and the pressure does not climb, suspect the valve itself.
• Supply pressure above the recommended 60 psi, or an air charge that does not match the incoming pressure. A. O. Smith lists both.
• A genuine over-temperature. If the water at the tap is scalding and the T&P is discharging, that points to a heating-control fault, not an expansion problem (our reading), and it is the more urgent of the two. Turn the heater off and get it looked at.
• Condensation mistaken for a drip. A. O. Smith’s manual says condensation on a cold tank should not be confused with a tank leak. A cold inlet sweating in a humid room can run down the tank and pool where a T&P leak would. Dry everything, watch for a heating cycle, and see where it starts.

🔴 Whatever the cause, do not cap, plug, or reduce the discharge line. A. O. Smith says the discharge opening must not be blocked or reduced in size under any circumstances. If the valve is faulty, replace the valve.

Doing other water heater work?

If you’re already draining the tank, the jobs pair naturally: a dead heating element is the usual cause of no hot water on an electric unit, and flushing sediment while it’s drained is free maintenance — see how to flush a water heater. Working the symptom from scratch: no hot water troubleshooting.

Not sure you actually have thermal expansion? Prove it before you buy a tank — a 24-hour max pointer gauge test records the overnight peak.

Replacing the whole heater rather than adding to it? A.O. Smith vs Rheem works through the brand choice, and the expansion tank is still on the list either way. The heater size you pick sets the row in the charts above; the water heater size calculator helps with that.

FAQ

Do I need an expansion tank on my water heater?

If a check valve, backflow preventer or pressure-reducing valve sits on the cold supply to the heater, you have a closed system, and the model codes call for thermal expansion control (IPC 607.3, UPC 608.3, IRC P2903.4). A. O. Smith says a tank must be installed on all closed systems, and Bradford White says not to run its heater in a closed system without a properly sized tank or other device. Your local code and your heater’s manual settle the details. A T&P valve that drips after the heater runs is a common sign of a closed system without one.

What is the small tank above my water heater?

Usually a thermal expansion tank. It is teed into the cold water line to the heater and holds the extra water that expands when the heater fires, which keeps the pressure below the relief valve setting. See the sizing charts and the precharge section on this page.

What size expansion tank do I need for my water heater?

It depends on three inputs: heater gallons, house supply pressure and thermostat setting. For a 40 or 50 gallon heater at 40 to 80 psi with the thermostat set no higher than 140°F, Amtrol’s chart lists 2.0 gallons, A. O. Smith lists 2 gallons for heaters up to 66 gallons at 40 to 60 psi, and Zilmet lists its ZEP5. An 80 gallon heater at 80 psi moves up to 4.4 gallons on Amtrol’s chart and 5 gallons on A. O. Smith’s. Use the chart of the maker whose tank you buy. Watts and Thrifco print no heater-size chart, so compare their volumes with the charts above. If you are unsure, Zilmet says to go to the next larger size.

What pressure should I set my expansion tank to?

Your house supply pressure, measured with no water running at a gauge on the house side of the PRV. Amtrol, Watts, A. O. Smith and Zilmet all say to match the air charge to it before the tank goes in, with no water pressure on the tank. Factory settings differ: Amtrol ships at 40 psi, A. O. Smith at 38 psi and Watts at 20 psi. Watts says never to go above an 80 psi air charge.

Why does my T&P valve keep dripping?

Often thermal expansion in a closed system, and replacing the valve will not stop it; Rheem’s manual says the same. A. O. Smith also lists a worn or lime-clogged valve, inlet pressure above the recommended 60 psi, and a tank air charge that does not match the incoming pressure. Never cap or plug a T&P valve. It is the tank’s safety device.

How do I know if my expansion tank is bad?

Use the maker’s check. Amtrol says a professional plumber should check the system and the tank yearly, reading the precharge only while the tank is isolated and empty of water. On its ST-5, ST-8 and ST-12 an InSight cap changes color when the tank should be replaced, though Amtrol says not to rely on the cap alone. Zilmet says to check the precharge and inspect the tank every six months. A tank that is corroded or damaged is a replacement, not a repair. A T&P valve that starts weeping again is another reason to check it.

How do I tell whether my system is open or closed?

Put a gauge on a hose bibb on the house side of the PRV and note the static pressure, run a lot of hot water, then let the heater recover with everything closed and read it again. On an open system the pressure returns to roughly where it started. On a closed one it climbs and stays up. This is our field check, not a maker procedure. A gauge with a peak-recording hand left on overnight makes it clearer.

Can I check the pre-charge with the tank installed?

Not while the water side is under pressure. Amtrol says to check the precharge only while the tank is isolated and empty of water, Watts says to adjust it only under zero system pressure, and Zilmet says a filled system’s tank must be isolated and emptied first. A. O. Smith’s method is to shut the main, open a faucet until the flow stops, then read the tank with a tire gauge. Amtrol notes that checking lets a little air escape, so check only as the maker directs.

Does the expansion tank go on the hot or cold side?

The cold supply to the water heater, downstream of the check valve, PRV or backflow preventer. IPC 607.3 says downstream of all of them, and the UPC says the building side of the device. Amtrol says that on the hot outlet the expanded water sits in the tank and cools, so hot water is not immediately available at the fixtures.

My pressure reads over 80 psi. Does a tank fix that?

No. An expansion tank absorbs the volume change from heating. It does not lower your standing supply pressure. IPC 604.8 calls for a PRV above 80 psi static, A. O. Smith says a PRV is required above 80 psi, and Watts says to add a PRV or put the tank on a riser below 80 psi. Fitting a PRV is often what closes the system and creates the need for the tank, so you may need both.

Sources

Read on 2026-09-29. Each spec, chart row and code quote on this page traces to one of these.

• 2021 International Plumbing Code, §607.3 Thermal expansion control (and §604.8, §504.4 and §504.5 at the same site): the wording quoted above.
• 2021 International Residential Code, §P2903.4 Thermal expansion control with §P2903.4.1 and §P2903.4.2.
• 2021 Uniform Plumbing Code (IAPMO/ANSI UPC 1-2021), Chapter 6: §608.2 and §608.3, read in IAPMO’s online viewer.
• Georgia State Amendments to the International Plumbing Code (2024 Edition) (Georgia DCA, revised January 1, 2026): §504.6 and §607.3 as amended.
• Georgia Plumbing Code 2024 (IPC 2024 with Georgia amendments), Chapter 6: §607.3 and §604.8, as posted by UpCodes.
• Amtrol Therm-X-Trol ST and T series installation and operation instructions (part 9015-942, 03/17; a distributor-hosted copy): precharge, location, mounting, sizing charts.
• Amtrol, Sizing the Therm-X-Trol Potable Water Expansion Tank (part 9017-112, 04/11): one-way devices, factory precharge, NSF 61, hot-side warning.
• Amtrol Therm-X-Trol Reference Guide (MC# 8550, 02/10): expansion figure, older model chart.
• Watts PLT-5, PLT-12, PLT-20 installation instructions (IS-PLT 0932): precharge, acceptance volumes, mounting, NSF 61.
• A. O. Smith water heater thermal expansion tanks owner’s manual (100306555): sizing chart, location, air-charge check, weeping T&P causes.
• A. O. Smith potable expansion tank sizing guide AOSEB55300 (March 2013): residential sizing charts, 38 psi factory charge, 24-hour pressure definition.
• A. O. Smith TW-series expansion tank brochure: side effects of excess pressure, 140°F sizing chart.
• A. O. Smith direct-vent gas water heater manual 326940-001: closed-system and thermal expansion sections.
• Bradford White gas water heater manual 238-51012-00V: closed-system warning.
• Bradford White electric water heater manual 238-55974-00C: closed-system warning and warranty note.
• Rheem gas water heater manual AP22543 Rev 04: Thermal Expansion section.
• Zilmet USA expansion tanks installation manual (rev. 9/25): potable vs hydronic, precharge, mounting, maintenance.
• Zilmet thermal expansion tank guide (undated sheet): quick sizing chart.
• Thrifco Plumbing 4906032 product page: specifications as the maker lists them.

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