Walk-in tub glossary

Threshold is the height you must step over to enter. Lower is easier, but no walk-in tub is zero-threshold — verify the actual number for the model against what the user can manage.

Inward vs outward door. Inward doors open into the tub, save floor space and are held shut by water pressure, but they narrow the entry and cannot be opened when the tub holds water. Outward doors give a wider entry but require clear floor space; This Old House prices outward-opening doors at $500–$2,000 extra and wheelchair-accessible doors at $1,000–$3,000 extra.

Gasket is the rubber seal around the door — the most common source of leaks and a routine replaceable part. Fill volume is how many gallons the tub holds; most are 40 to 80, averaging around 50, and it drives water heater sizing.

Fast fill / fast drain are powered options that shorten the wait, since normal fill and gravity drain each commonly take 10 to 15 minutes. Hydrotherapy is water jets; aerotherapy is air jets. Be careful with "ADA-compliant" as a product label: the ADA Standards apply to covered public and commercial facilities, not to private single-family homes, so the phrase on a residential tub is marketing rather than a legal requirement you must meet.

How to choose

Ask for the threshold height in inches

It is a specific number in the product spec. Compare it to what the user can actually step over.

Get fill volume in gallons

It determines water heater sizing, fill time, and water cost. Do not accept 'about the same as a normal tub.'

Understand door swing physics

Inward doors seal partly by water pressure and cannot open when full. That is a safety consideration worth discussing.

Ask what fast drain actually achieves

Get the stated drain time with and without the option, and confirm your waste line can support it.

Treat 'ADA-compliant' with caution

ADA Standards govern covered public accommodations and commercial facilities, not private homes. It is not a certification of suitability for your relative.