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Does your water heater need a vacuum relief valve?
Answer two questions about how cold water enters the tank. The checker reads IPC 2021 section 504.
The code language is short. IPC 2021 section 504.1 says an approved means, such as a cold water dip tube with a hole at the top or a vacuum relief valve installed in the cold water supply line above the top of the heater or tank, shall be provided to prevent siphoning.
Section 504.2 says bottom-fed water heaters and bottom-fed tanks connected to water heaters shall have a vacuum relief valve, and it must comply with ANSI Z21.22.
Many states and cities adopt the IPC, often with local changes, and others use a different plumbing code. Your local inspector has the final word.
PlumbingPicks spec score out of 10, from the Cash Acme, Watts and Zurn Wilkins spec sheets and the Watts product page, read Oct 24, 2026. It is not a customer rating or our own test.
Best for most water heaters
Cash Acme VR20
3/4 in. vacuum relief valve with dust cover, 22398LF
3/4 in. male NPT13 SCFM at 2 in. Hg200 psi inlet210°FDZR brass
Buy it if
You’re adding or replacing the vacuum relief valve on a residential water heater or storage tank.
Skip it if
The water runs hotter than 210°F, as on some commercial or steam-heated tanks. Pick the Watts or Zurn at 250°F.
The VR20 is the valve I’d put on most water heaters, and I’ve used it. It scored 9.5, the top score here.
Cash Acme’s spec sheet says it protects hot water supply systems and pressure vessels against negative pressure, the vacuum that can burn out heaters and collapse storage tanks, especially copper ones. Installed on the cold water supply line, it closes tightly under pressure and opens at a 1 in. mercury vacuum, letting air in to break the vacuum.
It’s the only pick that publishes its opening point. It’s certified to ANSI Z21.22/CSA 4.4 and NSF/ANSI 372, and listed by CSA. Cash Acme says every valve is tested for performance before shipping.
The body and cap are lead-free DZR brass with a stainless spring, a silicone seat disc and a polypropylene dust cover about 1.75 in. across that protects the slotted vent. It comes in 1/2 in. (22397LF) and 3/4 in. (22398LF) male inlets.
The sheet gives 13 SCFM at 2 in. Hg, a 200 psi maximum inlet pressure and 210°F. That temperature is the one place it trails the Watts and Zurn, which list 250°F. For a home water heater set at normal temperatures, 210°F is well above what the tank should ever reach.
Cash Acme recommends installing it upright. Its drawing shows 1-3/8 in. across the body and about 2-1/2 in. tall with the dust cover.
Ignore the Amazon listing’s wording. It talks about over-pressure and thermal expansion, calls the body bronze and says the valve reseals after pressure relief. Cash Acme’s own sheet says it’s a vacuum relief valve with a brass body. For thermal expansion you need an expansion tank, not this valve.
On Oct 24, 2026 the listing was sold by Amazon.com.
Best for the most venting air
Watts LFN36-M1
3/4 in. lead-free brass vacuum relief valve, 0556031
Watts’ product page lists two different working pressures
Not a backflow preventer, Watts warns
3/4 in. male NPT15 CFM200 psi water250°FLead-free brass
Buy it if
You want the most venting capacity, or the tank sees low-pressure steam, like a jacketed kettle or steam coil heater.
Skip it if
Your inspector asks for NSF/ANSI 372 paperwork by name. Cash Acme and Zurn print it on their sheets.
The LFN36-M1 is Watts’ water heater vacuum relief valve, and I’ve used it. It scored 9.2.
Watts’ ES-LFN36 sheet lists a venting capacity of 15 CFM for both sizes, the highest of the three. The valve permits air to enter and prevent vacuum conditions that could siphon the water out, collapsing a tank or water heater or burning out equipment.
It’s tested and rated to ANSI Z21.22 and CSA certified, with a lead-free brass body, a silicone disc, a 302 stainless spring, a Buna-N O-ring and a glass-filled polysulfone float under a polypropylene cover.
Watts lists more uses than the others: domestic water heaters and supply tanks, table top heaters, jacketed steam kettles, unit heaters, low pressure steam systems and steam coil heaters. The sheet gives a 15 psi maximum steam pressure and 250°F, and says to use a pigtail in steam service so live steam can’t damage the valve.
Two marks against it. Watts says “Lead Free” and that it meets lead-free installation rules, but the sheet doesn’t name NSF/ANSI 372 the way the other two do. And Watts’ product page lists 200 psi maximum working pressure in its description but 15 psi in its spec table; the 15 is the steam figure. The Amazon listing gives 200 psi for water, which matches the description.
The sheet carries an important note: vacuum relief valves are not designed or approved as backsiphonage backflow preventers. For that, Watts points to its 288A vacuum breakers. See vacuum breaker vs anti-siphon valve for the difference.
It’s about 2 in. across and 2 in. tall and weighs 4 oz, per Watts, and comes in 1/2 and 3/4 in. Amazon.com sold the 3/4 in. listing on Oct 24, 2026.
Best for 250°F and NSF 372 in 1/2 in.
Zurn Wilkins 12-VR10XL 1/2 in. vacuum relief valve
1/2 in. threaded13 CFM200 psi250°FLow-lead brass, ASTM B 371
Buy it if
Your tank has a 1/2 in. tapping and you want 250°F, 200 psi and NSF 372 together.
Skip it if
You need 3/4 in. The 3/4 in. VR10XL wasn’t in stock on Amazon when I checked.
The VR10XL is Zurn Wilkins’ vacuum relief valve, and I’ve used it. It scored 8.2.
Zurn’s TP-VR10XL sheet says it’s for commercial and residential water lines, protecting water supply systems and pressure vessels against internal vacuum that could drain a system by siphonage, burn out heaters or collapse storage tanks.
It meets ANSI Z21.22/CSA 4.4 and is certified to NSF/ANSI 372 by IAPMO R&T, with a body of low-lead brass to ASTM B 371, Buna nitrile and silicone elastomers, and 300 series stainless internals. It has the strongest ratings sheet of the three: 200 psi and 250°F, with 13 CFM capacity.
Zurn draws it at 2-1/2 in. tall and 1-1/4 in. across, with a 1 lb shipping weight. At 2-1/2 in. it’s taller than the 2 in. Watts, about the same as the Cash Acme with its cover.
It lost points on one check: Zurn’s sheet lists no vent cap or dust cover. The other two cover the vent so dust and debris stay out of the seat.
Zurn’s typical installation drawing shows it on the cold supply to a hot water storage tank alongside its TP220 relief valve and XT expansion tank. That’s the right company for it: the T&P valve handles over-pressure and over-temperature, the expansion tank handles thermal expansion, and this valve handles vacuum.
On Amazon only the 1/2 in. size was in stock, sold by Plumber’s Paradise, on Oct 24, 2026. Check your tank’s tapping or tee size before ordering.
Zurn lists its threads to ANSI B1.20.1, the standard tapered pipe thread, and names two of its T&P valves (TP1100A-4C and TP220-5C) and its XT expansion tank as matching accessories. Zurn lists its Buna nitrile and silicone elastomers to FDA 21 CFR 177.2600, the FDA rule for rubber parts meant for repeated contact with food.
The listing says CSA certified and ANSI Z21.22 rated, but I didn’t find an Eastman spec sheet to check capacity, temperature or pressure.
Cash Acme 2239LF listing
Its model number doesn’t match Cash Acme’s 1/2 in. part (22397LF), so I couldn’t tie it to the sheet.
“Fits LFN36-M1” look-alikes
Third-party valves sold as compatible with Watts, not genuine Watts parts.
Pressure vacuum breakers (Zurn 720A, 710)
Those are irrigation backflow devices, a different product.
What a vacuum relief valve does
1
Normal pressure
Water pressure holds the valve shut, so nothing leaks out.
2
The supply loses pressure
A main break, a drained line or a pump shutting off can pull a vacuum on the tank.
3
The valve opens
Cash Acme’s VR20 opens at a 1 in. mercury vacuum and lets air in.
4
The vacuum breaks
Air in the tank stops water from siphoning out and keeps the tank from collapsing.
5
Pressure returns
Water pressure closes the valve again.
All three makers describe the same failures it prevents: water siphoned out of the tank, burned-out heating elements or heaters, and collapsed storage tanks. Cash Acme singles out copper tanks. An electric element left running in a tank that has siphoned dry is one way that burnout happens.
Where the valve goes
Setup
Where the makers or code put it
Top-fed heater, no dip tube hole
On the cold supply line above the top of the heater or tank (IPC 504.1)
Bottom-fed heater or tank
Required (IPC 504.2); the makers show it on the cold side
Separate storage tank
On the tank’s supply; Zurn’s drawing shows it with the T&P valve and expansion tank
Steam kettles, coil heaters
Watts lists these uses; use a pigtail in steam service
Cash Acme says its VR20 goes on the cold water supply line and should be installed upright. Its Amazon listing says either side is fine, which doesn’t match the maker’s sheet. I’d follow the sheet and the code: cold side, above the top of the heater or tank where the code calls for that.
Use a tee in the cold line above the heater, with the valve pointing up. Wrap the male threads with thread tape or use a rated pipe dope, as with any threaded brass fitting; see Teflon tape vs pipe dope.
What a vacuum relief valve isn’t
Device
What it protects against
Can it replace a vacuum relief valve?
T&P relief valve
Too much pressure or temperature in the tank (IPC 504.4)
No
Thermal expansion tank
Pressure rise as heated water expands
No
Vacuum breaker / backflow preventer
Dirty water siphoning back into the drinking water
No, and Watts says a vacuum relief valve can’t replace it either
Dip tube with a siphon hole
Siphoning a top-fed tank (IPC 504.1)
Yes, for top-fed heaters only
People mix these up because they all sit near the water heater. A T&P relief valve lets water out when the tank gets too hot or too pressurized. A vacuum relief valve lets air in when the tank is being sucked empty. They do opposite jobs, and a bottom-fed heater needs both.
Choosing a size and a rating
Question
What to look for
Thread size
Match the tee or tank tapping: 1/2 or 3/4 in. male NPT. All three come in both; on Amazon the Zurn was 1/2 in. only.
Temperature
Watts and Zurn list 250°F; Cash Acme lists 210°F.
Pressure
All three list 200 psi for water.
Venting
Watts 15 CFM; Cash Acme 13 SCFM at 2 in. Hg; Zurn 13 CFM.
Lead-free paperwork
Cash Acme and Zurn name NSF/ANSI 372; Watts says lead-free.
Steam
Only Watts lists low-pressure steam use (15 psi).
For a home water heater, any of the three covers the job; pick by thread size and whether your inspector wants NSF 372 named on the sheet. For a steam kettle or coil heater, the Watts is the one with steam ratings.
Replacing a vacuum relief valve
1
Shut off the heater and water
Turn off power or gas, then close the cold supply valve.
2
Relieve pressure
Open a hot tap to drop the pressure in the line.
3
Unscrew the old valve
Use a wrench on the hex, not the cap.
4
Seal and install the new one
Seal the threads and install it upright, per Cash Acme.
5
Refill and check
Open the supply, purge air at a hot tap, then look for leaks at the threads.
A vacuum relief valve that drips or sprays when the system is under normal pressure isn’t sealing. The makers don’t publish a service life, so replace it when it leaks, and whenever you replace the water heater. See why is my water heater leaking if you’re not sure where water is coming from.
Materials, by maker
Part
Cash Acme VR20
Watts LFN36-M1
Zurn VR10XL
Body
Lead-free DZR brass
Lead-free brass
Low-lead brass, ASTM B 371
Seat / disc
Silicone disc, integral body seat
Silicone disc
Buna nitrile and silicone
Spring / internals
Stainless spring, brass parts
302 stainless spring
300 series stainless
Cover
Polypropylene dust cover
Polypropylene cover
None listed
DZR means dezincification resistant, a brass made to resist losing zinc in aggressive water. Silicone seats tolerate heat well, which matters on a valve that sits on a water heater.
How to tell if a heater is top-fed or bottom-fed
Clue
Top-fed
Bottom-fed
Cold inlet
On top of the tank, with a dip tube inside
Near the bottom of the tank
Common on
Most residential tank heaters
Some storage tanks
Code path
IPC 504.1: dip tube hole or vacuum relief valve
IPC 504.2: vacuum relief valve required
Where to confirm
The heater manual or data plate
The heater or tank manual
A top-fed heater sends cold water down a plastic dip tube to the bottom of the tank. A small hole near the top of that tube breaks a siphon, which is why IPC 504.1 accepts it as an anti-siphon means. A bottom-fed tank has no dip tube, so a siphon can pull water straight out of the bottom; that’s why 504.2 requires the valve.
A separate storage tank fed by a boiler or a tankless heater can be bottom-fed. Zurn’s typical installation drawing shows exactly that setup: a hot water storage tank with the vacuum relief valve on the cold supply.
Using a vacuum relief valve on steam equipment
Watts application
Note from the ES-LFN36 sheet
Jacketed steam kettles
Use a pigtail between the steam space and the valve
Unit heaters and steam coil heaters
Shown with a pigtail and a steam trap
Low-pressure steam heating
Maximum steam working pressure 15 psi
Under 5 psi steam
Watts says the pigtail isn’t needed below 5 lbs
Steam equipment can pull a vacuum as it cools, the condition Watts says the valve is there to break. Watts is the only maker here that rates its valve for steam, at up to 15 psi, and it calls for a pigtail so live steam can’t reach the valve’s seat.
Size on the pipe
Valve
Height
Width
Weight
Cash Acme VR20
About 2-1/2 in. with dust cover
1-3/8 in. body; cover about 1-3/4 in.
Not listed
Watts LFN36-M1
2 in.
2 in.
4 oz
Zurn Wilkins VR10XL
2-1/2 in.
1-1/4 in.
1 lb shipping
All three are small enough to fit in a tee above a residential heater. Leave room above the valve so its vent stays open; a valve buried in insulation or pressed against a ceiling can’t breathe in air when it needs to.
Questions people ask
What is the best vacuum relief valve?
On our spec score, the Cash Acme VR20 (9.5), then the Watts LFN36-M1 (9.2).
Is a vacuum relief valve required on a water heater?
On bottom-fed heaters and tanks, yes: IPC 504.2. Top-fed heaters need a dip tube hole or a vacuum relief valve under IPC 504.1.
Where does a vacuum relief valve go?
On the cold supply line, upright. IPC 504.1 says above the top of the heater or tank.
Is a vacuum relief valve the same as a vacuum breaker?
Match the tee or tank tapping, usually 1/2 or 3/4 in. male NPT.
Can a vacuum relief valve replace a T&P valve?
No. A T&P valve lets water out; a vacuum relief valve lets air in.
Why is my vacuum relief valve leaking?
A valve that leaks under normal pressure isn’t sealing. Replace it.
What does a vacuum relief valve open at?
Cash Acme’s VR20 opens at a 1 in. mercury vacuum. Watts and Zurn don’t publish an opening point.
Do I need one with a tankless water heater?
IPC 504 covers storage water heaters and tanks. A tankless unit with a storage tank may need one on the tank.
What standard should a vacuum relief valve meet?
ANSI Z21.22, which IPC 504.2 names. All three picks meet it.
How I picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all three picks. Every figure comes from the Cash Acme, Watts and Zurn Wilkins spec sheets and the Watts product page, read Oct 24, 2026, plus IPC 2021 section 504.
How I pick
ANSI Z21.22 vacuum relief valves for water heaters and tanks only.
Genuine maker listings, new and in stock on Amazon on the day of the update.
Every pick scores 7.0 or more on the spec score below.
Prices come from Amazon’s API with the time they were read.
The spec score, check by check
The six vacuum relief valve checks below each count for one sixth of the score. Each is scored 0 to 10 from the spec sheets, then averaged to one decimal. No bench test, no customer reviews.
Check (weight)
How it’s scored
ANSI Z21.22 / CSA (1/6)
10 if the maker states ANSI Z21.22 rating and CSA certification
Lead-free certification (1/6)
10 if NSF/ANSI 372 is named; 7 if lead-free is stated without it
Venting capacity (1/6)
15 CFM or more 10; 13 CFM 9
Max temperature (1/6)
250°F 10; 210°F 8
Max water pressure (1/6)
200 psi stated consistently 10; stated with a conflicting figure 8
