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What Size Water Heater Do I Need for My Walk-in Tub?

Updated September 2026

▶Glossary7
  1. Watch: Hot Water Capacity and Supply
  2. The Factors That Determine Your Water Heater Needs
  3. Our Sizing Recommendations
  4. How to Find Your Tub's Water Capacity
  5. What the In-Line Heater Does and Does Not Do
  6. Related Guides
  7. Common Questions

What size water heater do I need for a walk-in tub? For most homes the answer is a 75 gallon or larger tank, because a walk-in tub holds more water than many standard bathtubs and you want it filled hot before you settle in. Ella's Bubbles recommends the maximum capacity water heater available for your house, anything less than 75 gallons is not recommended, and the largest models such as the ShaK and the Big4Two may call for a dedicated large heater in addition to the one serving the rest of the home. One important point up front: the in-line water heater included with hydro massage tubs maintains your bath temperature while the hydro pump runs, but it never raises the temperature, so your house water heater does all the work of filling the tub hot. This article walks through the factors that matter, the sizing recommendations, tankless options and where to find your tub's exact water capacity.

Watch: Hot Water Capacity and Supply

Hot Water Capacity and Supply for Ella Walk-In Tubs
Chapters in this video
  1. 0:00 Hot Water Heater Capacity The video explains the recommended hot water heater capacity for an optimal walk-in tub bathing experience.
  2. 0:37 Finding Tub Water Capacity The video shows how to find the water capacity of Ella's Bubbles walk-in tubs on the website.
  3. 1:04 Dedicated Hot Water Supply The video suggests considering a dedicated hot water supply system for your walk-in tub.
  4. 1:16 Supply Lines And Faucet Sets The video recommends 3/4 inch supply lines and mentions included supply lines with Ella's Fast Fill faucet sets.

Key points from the video: Watch: Ella's Bubbles: Determining Correct Hot Water Supply For A Walk-In Tub with chapters and a full transcript.

  • With the water demands of modern homes, a professionally installed high capacity water heater gives you consistent, constant hot water delivery, especially for our larger tubs such as the Big4Two or the ShaK.
  • To check your tub's needs, visit the Compare Ella Walk-In Tubs page on ellasbubbles.com and click Compare Specs to see water capacity in gallons, both occupied and unoccupied.
  • Consider a dedicated hot water supply system just for the walk-in tub, or a combination of two systems, and always consult your installer or a professional plumber.
  • We recommend 3/4 inch supply lines with easily accessible shutoff valves. Ella 2-piece and 5-piece fast fill faucet sets include 5 foot supply lines.

The Factors That Determine Your Water Heater Needs

Every home is different, so there is no single answer that fits everyone. These are the factors that affect fill time and water temperature:

  • The size of the walk-in tub, meaning its occupied water capacity in gallons
  • The water pressure in your house
  • The supply piping size and configuration, for example 1/2 inch versus 3/4 inch
  • The distance from the walk-in tub to the water heater
  • The faucet on the tub, fast fill versus standard
  • The efficiency and capacity of your water heater
  • Whether other plumbing fixtures run at the same time

The supply side of that list is covered in water supply lines, shut-off valves and pipe size, and what a realistic fill looks like is in fast-fill faucet expectations.

Our Sizing Recommendations

  • Average size walk-in tubs: most homes need to replace a smaller existing heater with a 75 gallon or larger water heater.
  • Our largest models, such as the ShaK and the Big4Two: these may call for a dedicated large water heater in addition to the one already serving your house.
  • Tankless water heaters: electric and natural gas high efficiency tankless heaters can work, but they usually fill more slowly, so choose the highest flow rate available, 11 GPM or higher. A small on-demand unit rated at only a few gallons per minute will feel far too slow with a fast-fill faucet.

It is always recommended to upgrade toward the larger size once all the factors are considered. Please consult an experienced professional contractor to assess your home and recommend the best solution. For assisted bathing, Ella also offers systems with a dedicated pre-heated reservoir: the HomeCare 32x60 transfer tub carries an 80 gallon fast fill tank, and the CareGiver lay-down system has a side reservoir of about 105 gallons; our team can tell you whether one fits your project.

Illustration of the fast fill water heater reservoir tank used with an Ella assisted-bathing walk-in tub
For assisted bathing, a dedicated pre-filled reservoir delivers a full hot bath without waiting on the house heater.

How to Find Your Tub's Water Capacity

Every Ella walk-in tub lists its water capacity in gallons, both occupied and unoccupied, on its specification sheet and on the compare specs tool at ellasbubbles.com. Your occupied capacity is the practical number for hot water planning, since the bather displaces part of the volume. As a guide, the Elite holds about 75 gallons empty and 35 to 55 gallons with a bather, the Monaco about 55 to 85 gallons occupied, the Ultimate about 95 gallons empty and 55 to 85 occupied, and the Big4One about 75 to 100 gallons occupied. The complete list is in the water capacity guide by model. Make sure your hot water supply covers the tub plus the other fixtures and appliances in your home.

What the In-Line Heater Does and Does Not Do

Tubs with the hydro massage option include an in-line water heater. It is designed to maintain the temperature of the water already in the tub, and it only operates while the hydro massage pump is running. It will not make your bath warmer, so it is not a substitute for adequate house hot water capacity. Air massage tubs have no heater at all; the blower simply moves air. See how the in-line water heater maintains temperature for the full explanation, and will I get cold while the tub fills or drains for how the heated seat helps at both ends of the bath.

Ella walk-in tub in-line water heater unit with power switch, indicator light and stainless steel fitting
The in-line heater under the deck holds the bath at temperature while the hydro pump runs; it does not replace the house water heater.

If your home is on a private well or a septic system, see using an Ella walk-in tub with well water and a septic system for what to filter, flush and have your plumber confirm before installation.

Common Questions

Is a 40 or 50 gallon water heater enough?
It is not recommended. A 40 or 50 gallon tank may manage a partial fill when nothing else in the house is running, but for a full hot bath the recommendation is a 75 gallon or larger water heater, or the maximum capacity your home can accommodate. Please consult an experienced professional contractor or plumber to assess your home.
What size tankless water heater do you recommend?
Electric and natural gas high efficiency tankless heaters can work, but they usually fill more slowly than a large tank, so choose the highest flow rate available, 11 gallons per minute or higher. A small on-demand unit rated at only a few gallons per minute will feel far too slow with a fast-fill faucet and will noticeably stretch the fill time. Your plumber can confirm that the unit's flow rate and your supply piping match the demands of the tub.
Does the in-line water heater warm the bath?
No. The in-line water heater included with hydro massage tubs maintains the temperature of water that is already in the tub, and it runs only while the hydro pump is running. It never raises the temperature, so it is not a substitute for adequate house hot water capacity. Fill the tub with hot water from the faucet, then let the in-line heater hold that temperature during your hydro massage, and note that air massage tubs have no heater at all.
How many gallons does my tub hold?
Every Ella walk-in tub lists its water capacity in gallons, both unoccupied and occupied, on its specification sheet and on the compare specs tool at ellasbubbles.com. Typical occupied figures run from about 30 to 50 gallons on the compact models to 75 to 100 gallons on the Big4One and 80 to 120 gallons on the ShaK. Use the occupied figure for hot water planning, since the bather displaces part of the volume, and make sure your supply also covers the other fixtures and appliances in your home.
How long does the tub take to fill?
Typically 7 to 15 minutes, depending on tub size, water pressure, supply pipe size, the distance from the water heater and the capacity of the heater itself. It takes about 10 minutes to reach a level where the hydro jets are safe to use, and a few minutes more to reach the overflow. A fast-fill faucet, 3/4 inch supply lines and a heater with enough capacity all help, while running other fixtures at the same time lengthens the wait.
Does the water heater need to be close to the tub?
Closer is better, because the distance from the walk-in tub to the water heater is one of the factors that affect fill time and water temperature. A long run means waiting for hot water to arrive at the faucet as well as needing enough volume in the tank. If the heater is far from the bathroom, discuss pipe routing and insulation with your plumber, and consider whether a dedicated hot water supply for the tub makes sense for your home.
Is there an Ella fast-fill water tank?
Yes, for assisted bathing. The HomeCare 32x60 transfer tub carries an 80 gallon pre-heated fast fill tank, and the CareGiver lay-down system has a side reservoir of about 105 gallons, so a full hot bath does not wait on the house heater. For a standard walk-in tub the usual route is a larger house water heater, sized for the tub and the rest of your home. Share your model and project details with your Ella dealer or the team at (800) 480-6850, and they can tell you whether the reservoir fits your project.
Is there a recommended water heater temperature setting?
Ella's Bubbles does not publish a water heater setpoint. Water temperature at the tub is controlled at the faucet like any other bath, so set the heater with your plumber's guidance. If your faucet has a thermostatic control valve, use its anti-scald setting so the water delivered to the tub stays at a safe, comfortable temperature.
If I already have a water heater, do I need a second one just for the tub?
Not necessarily. Give your plumber the occupied water capacity printed on your model's spec sheet; that is the number of hot gallons one bath needs. If your tank falls short, a tankless heater tied into the hot line as a booster is one option, and for the largest tubs the team has suggested an 80 gallon tank, two 50 gallon tanks side by side or a tankless unit. Ella's Bubbles does not make or install water heaters.
Does the tank size matter more than the water pressure?
Both matter. The fast fill faucet can only deliver what your supply pressure and pipe size allow, so confirm the house has good pressure and 3/4 inch supply lines before you count on a quick fill. A hot shower taken right after a full bath on a small tank is where owners most often run short.

Still need help? Our team is always happy to assist. Open a ticket at ellasbubbles.com/support or call (800) 480-6850.

About this guide. Answers in the Ella’s Bubbles Support Center are compiled from real conversations with tub owners, our technicians’ notes and the product documentation, then reviewed by our team. Tub models and options have evolved over the years, so a detail here may differ slightly from your exact tub. If something looks different on yours, send us your serial number and a specialist will confirm it for your model.

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