Does a walk-in tub drain need its own vent or air admittance valve?

No. An Ella walk-in tub does not need a special vent of its own. Its drains connect to the house drain the way a conventional bathtub does, and it is that house line that must flow freely and be trapped and vented to local code by your licensed plumber. Whether an air admittance valve is an acceptable way to vent that trap is a local code question that your plumber and inspector decide, not something the tub requires or rules out. Does the Fast Dual Drain Overwhelm Standard Household Drain Piping? explains why the gravity design places no unusual demand on the drain system.

Three Different Things Called a Vent

Part of the confusion is that the word vent shows up three times around an Ella tub, and only one of them is a plumbing-code vent.

• The house drain vent. Every trap on a house drain needs venting to code, and the tub's drain is no exception. This is your plumber's work on the house side of the connection. The tub adds no vent requirement of its own; it simply needs a house drain that has been tested for free flow, trapped and vented to local code.
• The drain handle vent assemblies. Each chrome drain handle on the tub deck sits on a vent assembly that passes through the deck and is secured underneath by a retaining ring and lock nut, with the drain cable attached beneath it. The easy-turn drain handles double as air vents on the tub side, eliminating air pockets so the water flows out smoothly rather than in surges. These are part of the tub's drain hardware and work on the tub side only; the house trap still needs the venting your code requires.
• The hydro line vent valve. Under the deck, at the end of the hydro line, is a fitting that Ella's technical team describes as a vent for the hydro system. It is tied to the stainless steel frame at the highest level under the deck. It has nothing to do with the drain plumbing.

The drain cable replacement video on this page shows the second of these. The retaining ring nut on the vent is loosened and the drain vent assembly is lifted out of the deck, which makes clear that the vent on top of the tub is a small handle assembly with the cable attached, not a pipe your plumber has to connect.

What Your Plumber Actually Connects

Ella's Dual Drain Technology is purely gravity driven with no pump anywhere in the system. The water falls through the tub's 2 inch drains, and the house line accepts it at whatever rate its size and condition allow. For comparison, a standard house bathtub drain is 1.5 inches, and a 2 inch pipe carries about four times the volume of water of a 1.5 inch pipe. Ella tubs use two independent 2 inch drains: open the first and the tub drains at a fast pace, open the second and it goes faster still.

1. On dual drain models the two drains join under the tub into a single house connection, so there is one P trap and one reducing fitting, not two drain pipes.
2. A 2 inch house main is recommended for the fastest emptying, but a standard T or Y fitting into a 1.5 inch house drain works. The plumber fits a 2 inch to 1.5 inch reducing coupling on the tub side of the P trap riser, or runs a 2 inch PVC 90 off the drain body and reduces ahead of the trap.
3. A Y is preferred over a T because the water changes direction less.
4. The T type drain body accepts the house connection from either direction, and end caps close the unused ports.
5. There is roughly 3 inches of clearance under the tub for 2 inch PVC, so the run can go to either side.
6. The drains always sit on the side opposite the door as you face the tub: a right side door means left side drains, and a left side door means right side drains. Confirm the door side before roughing in.

Because nothing is pumped, the water is only ever moving under its own weight, and a pump or power failure can never leave you sitting in a full tub. That is also why a walk-in tub is treated like any other gravity fixture for venting: the trap and vent your local code requires for a bathtub are what it needs, and no more.

Slab Floors and Above-Floor Piping

The default installation keeps all piping above the floor and needs no cutting or access from below, which is why a concrete slab works. The leveling legs set the frame with about 3 inches of clearance beneath it, so one drain line coming up through the slab can be run to either side. Lowering the tub means putting the drain below the floor and trimming the apron, which affects the warranty on the altered parts. Where Does the Drain Sit for a Slab Installation? covers the layout, and What Plumbing, Electrical and Space Does a Walk-In Tub Installation Need? puts the drain requirements alongside the supply and electrical ones. Rough in dimensions come from the spec sheet and drawings for your model, so have those in hand before the pour or the rough in.

Symptoms That Get Blamed on Venting

When a tub drains slowly, gurgles or shows water underneath, venting is often the first guess. Most of the time the cause is somewhere else.

• Slow draining. Actual drain time depends on the tub's water capacity and on the condition and layout of the house drain. The fewer turns and the better the condition of your home's drainage, the faster the water leaves. The dual drain speeds up the tub side but cannot fix a slow house line, which is why Ella asks for the house drain to be tested for free flow before the tub goes in.
• A wobbly or spinning drain handle. That is the vent assembly on the deck, not the plumbing vent. Why Are My Drain Handles Loose and How Do I Tighten Them? covers the allen screw, the retaining ring and lock nut, and the cable behind the access panel.
• A drip under the tub that starts only when the water reaches the top jets. That points to the air manifold or the hydro line vent valve having dropped below its correct height, and Leak Under the Tub Only When Water Reaches the Top Jets explains the fix, which is re-securing them to the frame at the highest point under the deck.

If a question about venting or the drain connection comes up during installation, your plumber can call the team at (800) 480-6850 or open a ticket at ellasbubbles.com/support with your model, serial number and a photo or sketch of the drain layout. Ella does not send technicians, so the plumbing work stays with your local licensed plumber, and the team answers questions from you or your contractor.

Watch: Drain Cable Replacement with chapters and a full transcript.

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