How to Choose the Right Plumbing Outlet Box

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Whether you’re roughing in a new home or remodeling a laundry room, choosing the right plumbing outlet box ensures code compliance, simplifies installation, and delivers a clean, finished look.

This guide explains what to consider when selecting an outlet box, whether you're a DIYer, plumber, remodeler, or supplier.

What Is a Plumbing Outlet Box?

A plumbing outlet box, also called a supply box, provides a recessed area in the wall to connect water supply lines and drains for appliances like washing machines, refrigerators, dishwashers, and toilets. These boxes house valves and connections in one compact, accessible location.

Why Use a Plumbing Outlet Box?

Clean, Finished Look

One of the biggest advantages of a plumbing outlet box is its clean, streamlined appearance. Instead of exposed pipes and valves, everything is neatly contained within the wall for a more professional finish—ideal for kitchens, laundry rooms, and utility areas.

For a consistent look across any project, the Oatey MODA Supply Box System uses a universal white faceplate compatible with all box types. Whether you’re installing a washer, ice maker, lavatory, or toilet connection, the faceplate and footprint stay the same, delivering a uniform, compact look throughout the home or building.

Easy Access and Maintenance

Outlet boxes make it easier to reach water shutoff valves when service or emergency access is needed. Instead of searching behind appliances or in tight spaces, homeowners and contractors can quickly shut off water, minimizing potential damage and downtime. This accessibility also simplifies routine maintenance.

Faster, Easier Installation

Many outlet boxes are designed with features that help save time on the job. Pre-installed valves, snap-lock faceplates, and tool-free test plugs make installation faster and more efficient, especially in rough-in environments. With consistent sizing and layout flexibility, boxes like Oatey MODA simplify both new construction and retrofit work.

Space Efficiency

Recessed designs allow appliances like washers and refrigerators to sit closer to the wall, maximizing available space and improving functionality in laundry rooms, kitchens, and utility areas.

Versatility

Outlet boxes are available in a range of configurations to suit different fixture types, wall depths, and plumbing setups. Whether you’re working in a fire-rated wall, tight framing, or a modular multi-unit build, there’s a solution to match. Oatey offers versatile options like Quadtro, Eliminator, and Centro II to fit nearly any installation scenario.

What to Consider When Choosing an Outlet Box

Choosing the correct box depends on several key factors: the type of fixture, plumbing layout, installation environment, space constraints, and future service needs.

1. Identify the fixture type —

Start by matching the outlet box to the fixture:

Washing machines require hot- and cold-water supply lines and a drain connection.
Ice makers need a cold-water line in a compact configuration.
Dishwashers, kitchen sinks, and lavatories may require various supply options and drainage configurations.
Toilets generally require a single cold-water line.

The Oatey MODA Supply Box System’s modular design and consistent faceplate across applications make fixture planning easier.

2. Understand supply and drainage configuration —

Consider how the water will be supplied and where it needs to drain, especially in washing machine installations.

Most Oatey washing machine outlet boxes (WMOB) support common piping materials (PEX, CPVC, copper) and come with or without water hammer arrestors. If your supply comes from above, look for boxes that support inverted installation. Most Oatey WMOBs are invertible, except the Eliminator and fire-rated MODA models.

If your layout requires additional drainage, such as for condensate lines, choose a box with multiple knockouts. The Oatey Eliminator supports dual drainage with a single-point connection, while the 2x4 WMOB includes knockouts in all four corners for added flexibility.

For maximum adaptability, the Oatey Quadtro WMOB allows valve positioning on either side of the drain, straddling it, or from above, making it one of the most versatile boxes available.

3. Match the box to your pipe material —

Understand the type of plumbing pipes in the building. Are you working with copper, CPVC, or PEX? This will determine the type of valve connections you need. Oatey’s Quadtro Washing Machine Outlet Box allows valves to support layouts requiring the drains to be positioned to the left or right or centered on the drain pipe, or even to come from above.

4. Consider structural and spatial constraints —

Wall cavity depth, stud layout, and wall construction all affect box selection. For example, MODA boxes can straddle studs, be installed over-under, or mounted on separate walls, thanks to their modular design. If space is tight, the Centro II offers a compact form without compromising durability.

Here are six examples of different types of washing machine installations and options MODA offers from a layout perspective:

5. Factor in special requirements —

In multi-family or commercial buildings, fire-rated walls may require UL-classified outlet boxes. Oatey fire-rated outlet boxes, made with Bulk Molding Compound (BMC), are designed for these environments. They include UL-listed insulating and intumescent components, offering a plastic alternative to traditional metal boxes.

There is a widespread belief that metal outlet boxes are the sole fire-rated option available. Through this blog, we seek to debunk this misconception and shed light on the effectiveness of fire-rated, plastic outlet boxes.

6. Prioritize ease of installation —

Look for time-saving features like pre-installed valves, snap-lock faceplates, and tool-free test plugs to reduce labor costs and streamline installation. Oatey’s supply boxes are designed with installers in mind, providing consistent sizing across product lines to simplify prep and rough-in.

For maximum efficiency, opt for a system with a uniform footprint across all applications. Whether you’re roughing in a washing machine, ice maker, lavatory, kitchen sink, dishwasher, or toilet, the Oatey MODA Supply Box System delivers a clean, coordinated look throughout the entire project.

7. Plan for future maintenance

Removable and replaceable components make servicing easier down the line. Oatey’s MODA system features LocPin™ technology, which allows valve replacement without damaging finished walls.

Plastic vs. Metal Outlet Boxes

Each material has its place depending on application needs:

Feature	Plastic Boxes	Metal Boxes
Cost	More affordable	Generally more expensive
Corrosion Resistance	Excellent (noncorrosive)	May corrode over time
Fire Rating	Available in UL-rated options	Commonly assumed to be fire-rated
Installation	Lightweight, easy to install	Heavier and more rigid

Contrary to common belief, fire-rated plastic outlet boxes are a reliable, code-compliant option. Oatey’s BMC fire-rated boxes meet the same standards while offering easier handling and reduced weight, compared to their metallic counterparts.

Oatey outlet boxes are available at major home improvement retailers and plumbing wholesaler-distributors. Whether you’re a homeowner working on a renovation or a contractor stocking materials for a new build, Oatey offers reliable solutions for every job.

For more installation help, explore How to Install a Washing Machine Outlet Box or browse our full line of Oatey Supply Boxes.

Frequently Asked Questions

What is a plumbing outlet box used for?
- A plumbing outlet box is a recessed or surface-mounted box that houses water supply valves and drainage connections for appliances like washing machines, ice makers, and dishwashers. It keeps plumbing connections organized and hidden inside the wall, providing easy access for maintenance while creating a clean, professional appearance. Outlet boxes also help installations meet plumbing codes by ensuring proper valve placement and backflow prevention.
Are plastic outlet boxes code-compliant?
- Yes, plastic plumbing outlet boxes—such as those made from high-impact polystyrene (HIPS) or Bulk Molding Compound (BMC)—can be code-compliant, including in fire-rated wall assemblies. Products like Oatey’s fire-rated outlet boxes meet UL fire safety standards and include features like intumescent pads and UL-listed insulation. These plastic boxes are lightweight, corrosion-resistant, and easier to install than metal alternatives—without sacrificing performance or compliance.
How do I choose the right washer outlet box?
- Consider your water supply configuration (e.g., coming from above or below), drain requirements, and wall-cavity space. Look for models compatible with your pipe type (PEX, copper, or CPVC) and layout needs. For example, the Oatey Quadtro WMOB allows flexible valve positioning, while the Oatey Eliminator supports dual drain lines. A low-profile model like the Centro II is a smart choice in compact spaces.