Plumbing and hot water for a walk-in tub with shower
Short answer: in most homes a walk-in tub with shower connects to the same drain and water lines the old tub used. The things that change the job are: which end the drain is on, adding or replacing a shower valve in the wall, a dedicated electrical circuit if the tub has jets or a heater, and having enough hot water. Walk-in tubs hold more water than a regular tub, so the water heater is the most common surprise.
The plumbing checklist
| Item | Usually | When it gets bigger |
|---|---|---|
| Drain | Reuses the existing tub drain. | The new tub drains on the other end, or the drain line is old and needs replacing once the floor is open. |
| Hot and cold supply | Connects to the existing lines at the tub wall. | Very old or undersized supply pipes that cannot keep up with the tub filler. |
| Shower valve | Many combos use the existing valve location or the tub’s own deck valve with a diverter. | A new wall valve and riser for a fixed head, or moving controls to where a seated bather can reach them. |
| Anti-scald protection | Shower and tub-shower valves must be pressure-balanced or thermostatic under the plumbing code. | An old valve that does not meet current code may have to be replaced. |
| Electrical | None for a soak-only tub with no pump or heater. | Jets, a heated seat or an in-line heater usually need one or two dedicated GFCI-protected circuits. |
| Floor | A sound floor carries the filled tub and bather. | Soft spots, old water damage or a weak subfloor found when the old tub comes out. |
| Permit | Depends on your city and how much plumbing or electrical work is done. | New circuits or relocated plumbing are more likely to need one. Your installer should know local rules. |
Hot water: the item most often missed
A standard bathtub holds roughly 25 to 45 gallons. Walk-in tubs run deeper: the spec sheets we track list 30 to 90 gallons with a bather seated, and most of every warm bath comes from the water heater. On a combo the heater also serves the household’s showers, so the real test is the busiest hour, not the tub alone.
- Tank heaters: compare the bath plus any showers in the same hour with the first-hour rating on the EnergyGuide label.
- Tankless heaters: they do not run out, but their flow at your winter temperature rise sets how fast the tub fills.
- In-line heaters: they keep a full tub warm while you soak; they do not heat the fill.
The water heater check for a combo runs the numbers for tank and tankless heaters, with published tub capacities.
Plumbing questions to ask before you sign
- Is the tub ordered with the drain on the same end as my current drain?
- Is the shower valve new, and is it pressure-balanced or thermostatic? What maximum temperature is it set to?
- Where will the controls be, and can I reach them from the seat?
- Does this tub need its own electrical circuit? Is that included in the quote?
- What happens to the price if the floor or drain line is in poor shape once the old tub is out?
- Who pulls the permit, if one is needed?
Our homepage FAQ covers related installation questions, including whether a walk-in tub needs its own circuit.
The Better Business Bureau accredits Aging Safely Baths. Tap the seal to read our BBB profile before you call.
Sources
- Standard bathtubs of roughly 25 to 45 gallons: Retirement Living, How many gallons does a walk-in tub hold? Walk-in tub capacities: manufacturer spec sheets listed on the water heater sizing page.
- In-tub heaters and mixing valves for walk-in tubs: City of Boca Raton, Walk-in tubs and water heater sizing (PDF).
- Shower and tub-shower valve requirements: International Code Council, 2021 International Plumbing Code, section 412.3 (PDF).
Questions people ask
Does a walk-in tub with shower need special plumbing?
Usually not special, just complete. It connects to the existing drain and supply lines. The extra pieces are the shower valve and heads, and possibly an electrical circuit for jets or a heater. Moving the drain or adding a wall valve makes the job bigger.
What size water heater do I need for a walk-in tub?
Compare the hot water for one full bath, plus any showers in the same hour, with the first-hour rating on the heater's EnergyGuide label. With typical temperatures about three-quarters of a warm bath comes from the heater, so a 60-gallon bath needs roughly 45 gallons of hot water. Your plumber confirms it for your home.
Will a tankless water heater work with a walk-in tub?
It can, if its flow rating at your winter water temperature keeps up with the tub filler. If not, the tub fills slowly or runs cool. Ask the installer to compare the two numbers.
Can the shower and tub share one valve?
Yes. Many combos use one valve with a diverter that sends water to the tub filler, the hand shower or a fixed head. Make sure the diverter is easy to operate with a weak grip.
Does an in-line heater fill the tub with hot water?
No. An in-line heater keeps water that is already in the tub warm while you soak. The hot water for the fill still comes from your water heater.
Want us to look at your plumbing questions?
Tell us your water heater size and send a photo of the tub faucet wall. We can usually spot the big items before anyone opens a wall.