What size smart water shutoff valve do I need?

Two answers circulate, and only one is about the pipe#

The first answer says measure your pipe and buy the valve with the same number on it. The second says pipe size barely matters, because one adapter fixes everything. Each is right for one kind of product and wrong for the other.

Inline valves replace a section of your main water line. Moen says installation "requires removing a section of your main water pipe". For these, the first answer holds, with one catch: the number you are matching is a nominal trade size, not a measurement. A 3/4 in copper main is not 3/4 in across.

Actuators do not touch the pipe at all. They bolt over the handle of the shutoff valve you already have and turn it with a motor. For these, the pipe size is close to irrelevant, and the questions that decide fit are what kind of valve you have, how big it is, and how much room is around it. Buying an actuator by pipe size, and then finding a round-handled gate valve on the wall, is the mistake the second half of this page exists to prevent.

The inline valves: what size each one takes#

As published on each maker's product pages and spec sheets, read in October 2026. Prices are each maker's own store in US dollars.

Four things come out of that table:

1. Every Moen size is a maximum, and Moen disagrees with itself about the maximum. Its shop page says the 3/4 in model "is compatible with ¾ inch or smaller pipe diameter". The same model's spec sheet says it goes on a line "that is 0.75 inch diameter (can be installed on 1.25 inch diameter or smaller)". The 1 1/4 in model's listing gives both "1 ¼ inch or smaller" and "1.5 inch or smaller" on one page. Use the shop page's stricter figure, which is the one Moen puts in front of buyers, and buy the size that matches your main: it is the cheapest unit that fits, and its tailpieces arrive in your size.
2. Phyn is the only one-size design. Its 1 in NPSM ends take adapters to your pipe, and Phyn's fittings table lists two male adapters per install, by material: solder for copper, crimp for PEX, solvent weld for CPVC. Galvanized steel gets a separate warning to hire a plumber.
3. Sinopé is the only maker here selling a PEX-ended version, which saves two threaded joints on a PEX main. Its Zigbee fact sheet gives the PEX model as type B.
4. Pressure is a real limit. Moen's spec sheets give a maximum operating pressure of 175 psi, while its installation sheet recommends the device for a maximum continuous pressure of 80 psi. Moen also says Flo goes "after water meter, water shut-off and pressure regulating valve (if applicable)", so a house with a pressure regulator puts Flo on the regulated side.

How to tell 3/4 in from 1 in without a caliper#

Nominal size is a trade name. Phyn puts it plainly: "a pipe's name (e.g., '3/4 inch pipe') is its 'nominal size,' not its actual measurement." Moen suggests looking first at the shutoff valve or pressure regulator, which may be marked with the pipe size, then measuring the circumference "using tailor's tape or a string".

Sinopé publishes the conversion. Wrap a string around a straight run of pipe, away from fittings, which make it look bigger, and compare:

Divide the copper figure by pi and a 3/4 in copper line works out to 0.875 in across, and a 1 in line to 1.12 in. That gap is why "it measured about an inch, so it is 1 in pipe" is the most common sizing mistake: a 3/4 in main measured with a tape across its face reads close to 7/8 in, and a 3/4 in steel main reads more than an inch.

The actuators: your valve decides, not your pipe#

An actuator is the renter-friendly, no-plumber option: no pipe is cut and the original valve stays. That is also its limit, because the actuator can only turn a valve that turns well.

What the actuator table settles:

• A gate valve rules out every actuator here. Zooz says "ball valves only", AcuRite says "inline ball valves", YoLink says "existing ball valve". Phyn's guide describes the difference: a gate valve "has a round, wheel-like handle", a ball valve has a straight lever and closes with a quarter turn. If yours has a wheel, the choice is a plumber swapping in a ball valve, which is a pipe-cutting job anyway, or an inline unit.
• The valve has to work before the motor touches it. YoLink's guide says the existing ball valve "must open and close smoothly, with minimal effort, and it must close fully", and that the operator "is not able to correct mechanical issues". Zooz gives the numbers: a normal valve needs about 1.5 to 3.5 N·m, a "super stiff" one 5 to 6 N·m, "at this level, you can hardly move it by hand". The Titan's 6 N·m covers the stiff case. AcuRite's top figure lands just under it.
• Plastic pipe can twist under the motor. Zooz says yes to PVC, no to CPVC, and that PEX "all depends on pipe material quality/hardness", with PEX C recommended and B possible if the valve is not on a long flexible run. AcuRite names metal valves only.
• AcuRite's "O.D." wording does not match a nominal size. By Sinopé's table a nominal 3/4 in copper line is 0.875 in outside diameter, so a literal 3/4 in O.D. pipe is not a standard 3/4 in copper main. Ask AcuRite which it means before buying for a 3/4 in copper line.

YoLink's range is the widest, up to 2 in, which makes it the one to check first on a larger main or a commercial-style valve.

Where the valve goes#

The location rules matter as much as the size, and the well rules are the ones most guides leave out:

• After the meter and the main shutoff, before the first branch. Phyn installs "right after your water meter or where the water enters your home and before your pipes split off". Moen adds "after... pressure regulating valve (if applicable)".
• After a fire sprinkler branch. Phyn allows installation with a standalone sprinkler system only "as long as it is placed after where your sprinkler line branches off". An automatic shutoff upstream of sprinklers could shut them off.
• Wells: after the pump, the tank and the treatment. Moen's spec sheets say a Flo on a well or irrigation line goes downstream of filtration, after the pump and storage tank, and if it must go before a filter, a wye strainer "with a 100 mesh or finer screen and blow-down port is required".
• Indoors, or rated for outdoors. Moen keeps the device and power supply between 32°F and 140°F, and needs an outlet within 6 ft (3/4 and 1 1/4 in models) or 10 ft (1 in model). Sinopé's Zigbee valve is "indoor installation only" at 32°F to 104°F. The Zooz Titan is IP66 and sold for outdoor use.

What keeps it closing when the power or internet goes out#

A shutoff that needs Wi-Fi and wall power to close is exactly the thing that fails in the storm that floods the basement. The backups, as each maker states them:

Moen Flo and the AcuRite actuator both join 2.4 GHz Wi-Fi only, so if setup stalls on a mesh router, the 2.4 GHz pairing fix applies, along with the other costs of Wi-Fi devices. Sinopé's fact sheet is the bluntest about the trap: without a backup supply on the gateway, "the shut-off signal cannot reach the valve" in a power failure. The general case for keeping safety automations off the cloud is in what still works when the internet goes down and local versus cloud control; the outage page names water valves among the things never to leave on its two most cloud-dependent rungs.

Which one, by situation#

1. 3/4 or 1 in main, lever-handle ball valve, room around it: an actuator. The Zooz Titan if you run a Z-Wave hub such as Home Assistant or Hubitat, because its wired probe works with no network at all; YoLink if you want the wider valve range and its own hub. Either avoids cutting pipe, which also suits a rental where the landlord has agreed to the valve but not to plumbing.
2. Gate valve, corroded valve or no clearance: an inline valve, because the plumber is coming anyway. Moen Flo or Phyn if you want flow monitoring, a Sinopé valve if you want a plain shutoff on Zigbee or Sinopé's own Wi-Fi system.
3. 1 1/4 in main: Moen's 900-002, Phyn Plus with adapters, or an actuator on an existing 1 1/4 in ball valve. Sinopé stops at 1 in.
4. Larger than 1 1/4 in: YoLink's EVO, which lists up to 2 in, or Moen's 900-002 within the 1.5 in its spec sheet allows.

Whatever you buy, it is only as good as what tells it to close. Put leak sensors with a local siren at the low points first; a valve with nothing to trigger it is a remote-control tap. Matter has included water valves since version 1.3, as the Matter version history records, but none of the makers read here lists Matter on the pages above, so plan around each one's own app or hub, and check whether you need a hub at all before buying one for a single valve.

Where this page stops#

• US and Canadian products read from first-party pages and documents, as of October 2026: Moen, Phyn, Sinopé, YoLink, Zooz and AcuRite. Alarm.com's valve, Phyn's larger Protect XL models and other brands were not read, so the page makes no claim about them.
• Nominal sizes only. The string table is Sinopé's; other makers publish no conversion.
• Not plumbing code. Whether an inline valve needs a licensed plumber and a permit where you live is a local rule. Moen and Phyn both recommend a professional.
• Prices change. Moen's 1 1/4 in model costs $364 more than its 1 in, which is the one figure here most likely to move. Check the model on the box, as the buying checklist says for every device.