Which Size Moen Flo Fits My Main Water Line?

A homeowner we worked with recently bought their own Moen Flo because their insurance carrier required an automatic water shutoff. The trouble was the size. The device has to match the main line that feeds the house, and theirs didn't.

Before you order one yourself, here is how the sizes break down and how to tell which one your home needs.

What sizes does the Moen Flo come in?

Two. Moen currently makes a smaller unit and a larger unit, and nothing in between.

The smaller unit is the 3/4-inch device. It installs on either a 3/4-inch line or a 1-inch line, with a different adapter for each size.

The larger unit is the 1-1/4-inch device. It installs on 1-1/4-inch mains, and it also works on 1-1/2-inch mains.

Is there a Moen Flo for a main bigger than 1-1/2 inches?

Not yet. Moen doesn't have a unit built for anything above 1-1/2 inches. If your home has a main that large, find that out before you spend money on a device.

How do I know which size my main line is?

Look at the pipe at your main riser, the spot where your whole-house shutoff is. On most homes that's at the front of the house, and it's the same place the device gets installed.

If you can't tell the size by looking at it, have a plumber confirm it before you order. Guessing is how people end up with the wrong unit.

What happens if you buy the wrong size?

We saw exactly this in North Fontana, in the new condos going up above the 210 off Sierra, near Duncan Canyon Road. The homeowner's insurance carrier would only underwrite the policy if an automatic shutoff went on the water system. They ordered the smaller unit, the one made for 3/4-inch and 1-inch lines. The house has a 1-1/4-inch main.

The good news is that a mismatch usually costs the owner nothing but a headache. In most cases you can send the device back and buy the correct one.

Plan for the difference in price, though. The larger unit runs roughly $300 more than the smaller one, so a home with a bigger main needs a bigger budget for the device itself.

What should you check before you buy your own smart water shutoff?

Four things decide whether the device you buy will work in your home: pipe size, power, Wi-Fi and location.

Pipe size: The smaller unit is for 3/4-inch and 1-inch lines. The larger unit is for 1-1/4-inch and 1-1/2-inch mains.

Power: The valve needs an outlet close enough to reach where it will be mounted.

Wi-Fi: Stand where the device will go and check your phone. You want at least 2 bars at that spot.

Location: It belongs on the main supply for the whole house. We have found these on hot water lines and sprinkler lines, where they protect nothing.

Our smart water shutoff installation page covers the best place to mount the valve and what we do on install day.

Does water pressure matter for a Moen Flo?

Yes. These units are rated for a maximum of 80 psi. When the pressure regulator on the main is bad, or the house doesn't have one, a new regulator goes in as part of the install.

On a larger main, that matters for your budget. Regulators that are 1-1/4 inches and up start around $850 and can run as high as $3,000. Our water pressure regulator page explains what the regulator does and why it matters.

What if your insurance requires an automatic shutoff?

Find out the size of your main before you order anything. Then match the device to it: the smaller unit for 3/4-inch and 1-inch lines, the larger unit for 1-1/4-inch and 1-1/2-inch mains.

If you've already bought a device and you aren't sure it fits, have us check the size of your main. We are a Moen-registered installer, going on two years now, and we work in Fontana and the surrounding cities. Call (909) 600-4561.