The Math Problem Nobody Mentions
Walk-in tub salespeople love to talk about jets, heated seats, and chromotherapy lighting. They don’t love talking about the part where you sit naked in a cold tub waiting for it to fill because your water heater can’t keep up.
Here’s the math. A typical walk-in tub — a Kohler Walk-In Bath, a Safe Step, an American Standard Liberation — holds 50 to 80 gallons of water. You mix hot and cold, so roughly 70% of that needs to come from your water heater. For a 60-gallon tub, that’s 42 gallons of hot water. All at once.
A standard 40-gallon tank water heater can deliver about 28-30 gallons of hot water before the temperature drops. A 50-gallon tank gets you about 35-38 gallons. Neither one is enough to fill a walk-in tub without going cold halfway through.
And here’s the part that really matters: you can’t get out of a walk-in tub to adjust the temperature. The door seals when the tub is full. You’re sitting in it while it fills. If the water goes cold at gallon 35, you’re stuck in cold water until it drains enough to open the door.
Ask about water heater capacity before you sign anything. We’ve heard from Sacramento-area families who spent $8,000-$15,000 on a walk-in tub and didn’t find out about the water heater problem until the first bath. By then the tub was installed and the contractor was gone.
What’s in Most Sacramento Homes?
Sacramento’s housing stock is heavy on 1950s-1970s ranch houses. Arden-Arcade, Carmichael, Fair Oaks, Citrus Heights — these neighborhoods are full of single-story homes built with 40-gallon gas water heaters. Some have been upgraded to 50-gallon tanks, but plenty haven’t.
If your water heater has a label on it, check the gallon capacity. It’s printed right on the front. If the label is gone or unreadable, measure the tank: a 40-gallon gas unit is about 20 inches wide and 50 inches tall. A 50-gallon is the same width but about 6 inches taller.
Most of these older Sacramento homes run natural gas (PG&E) for the water heater. That matters when you’re deciding between a bigger tank and a tankless unit, because gas tankless heaters need a specific vent size and gas line capacity that your 1960s ranch might not have without upgrades.
Your Three Options
Option 1: Tankless water heater ($2,000-$4,500 installed)
A tankless unit heats water on demand. No tank, no running out. As long as water is flowing, it’s hot. For a walk-in tub, this is the gold standard.
In Sacramento, a gas tankless water heater (Rinnai RU199iN, Navien NPE-240A, Noritz EZ111) installed by a licensed plumber runs $2,000 to $4,500. The unit itself is $1,000 to $2,000. The rest is labor, venting, and potentially upgrading your gas line.
The gas line upgrade is where costs can spike. Older Sacramento homes often have a 1/2-inch gas line to the water heater. Most tankless units need 3/4-inch. Running a new gas line from the meter adds $300 to $800. You’ll also need a new vent — tankless units use stainless steel category III venting, not the B-vent your old tank uses.
Option 2: Bigger tank water heater ($800-$1,500 installed)
Swapping your 40-gallon tank for a 75-gallon tank is the simplest fix. A 75-gallon gas tank water heater (Rheem, A.O. Smith, Bradford White) costs $600 to $900 for the unit, plus $200 to $600 for installation.
Two things to check: Does the bigger tank fit in the same spot? A 75-gallon unit is wider and taller. In a tight garage corner or closet, it might not work without moving things around. Also, check your gas line — a 75-gallon heater has a bigger burner and may need more gas flow than a 40-gallon.
Option 3: Walk-in tub with inline heater
Some walk-in tubs come with a built-in inline heater. This is a small electric heating element that recirculates the water in the tub and keeps it warm. It doesn’t replace your water heater — you still need enough hot water to fill the tub initially — but it keeps the bath warm during a long soak.
Kohler, Safe Step, and American Standard all offer inline heater options. It adds $300 to $800 to the tub price. If your current water heater can almost fill the tub (say a 50-gallon tank with a 60-gallon tub), an inline heater might be enough to bridge the gap.
But if you’ve got a 40-gallon tank and a 75-gallon tub, the inline heater won’t save you. You’ll still run out of hot water during the fill. The inline heater only maintains temperature; it doesn’t heat cold water fast enough to make up a 30-gallon deficit.
Gas vs Electric Water Heaters in Sacramento
Sacramento is a gas town for water heating. PG&E natural gas is available in most of the metro area, and gas water heaters recover faster than electric (meaning they reheat a new tank of water more quickly).
Electric water heaters exist here too, especially in newer construction and areas served by SMUD. But electric tank heaters recover slowly. A 50-gallon electric unit takes about an hour to fully reheat. Gas takes 30-40 minutes. For a walk-in tub, that recovery time matters if anyone else in the house needs hot water after your bath.
Electric tankless is an option but it requires serious electrical work. Most whole-house electric tankless units need 150-200 amps. Plenty of older Sacramento homes only have a 100 or 150-amp main panel. Upgrading the panel adds $1,500 to $3,000 to the project. For most Sacramento homes, gas tankless is the simpler path.
What to Ask the Contractor Before You Buy the Tub
Any walk-in tub contractor who doesn’t bring up your water heater during the sales visit is either careless or hoping you won’t ask. Here are the questions:
1. “How many gallons does this tub hold?” Get the exact number, not “enough.” Check it against the spec sheet.
2. “What size water heater do I need for this tub?” They should know. If they say “your current one is probably fine” without checking, that’s a problem.
3. “Is a water heater upgrade included in this price?” Some contractors bundle it, some don’t. Get it in writing either way.
4. “Does this model have an inline heater option?” If so, what does it add to the price? Does it eliminate the need for a water heater upgrade?
5. “Who handles the water heater — you or a separate plumber?” Some walk-in tub companies subcontract the plumbing. That’s fine, but make sure someone is responsible for making sure the whole system works together.
Bottom Line
A walk-in tub without enough hot water is an expensive mistake. Before you sign a contract, check the label on your water heater and compare it to the tub’s gallon capacity. If the numbers don’t work, factor in the cost of a water heater upgrade — $800 to $4,500 depending on which route you take.
The best contractors bring this up on the first visit. If yours doesn’t, bring it up yourself. And remember: don’t pay more than $1,000 or 10% of the contract price upfront. That’s California law (B&P Code 7159), and it applies to the tub, the water heater, and everything else in the project.
Frequently Asked Questions
Most walk-in tubs hold 50 to 80 gallons when filled to bathing level. Compact models (Kohler Belay, American Standard Gelcoat) hold closer to 40-50 gallons. Larger hydrotherapy tubs can hold 80-100 gallons. The spec sheet will list the exact capacity.
For a standard 50-80 gallon walk-in tub, you need at least a 75-gallon tank water heater or a tankless unit rated for 5+ gallons per minute. A 40-50 gallon tank won’t produce enough hot water to fill the tub without going cold.
$2,000 to $4,500 installed. The unit runs $1,000-$2,000 (Rinnai, Navien, Noritz are the common brands). Installation adds $1,000-$2,500, which includes venting, gas line work, and permits. Gas line upgrades from 1/2-inch to 3/4-inch add $300-$800 in older Sacramento homes.
Yes, but they only maintain water temperature — they don’t heat cold water fast enough to fill the tub. If your water heater can almost fill the tub (50-gallon tank, 60-gallon tub), an inline heater bridges the gap. If there’s a big mismatch (40-gallon tank, 75-gallon tub), you still need a water heater upgrade.
Decide on the tub first so you know the gallon capacity, then size the water heater to match. Ideally, buy and install both at the same time. Some contractors handle both and can bundle the labor. Don’t buy the tub first and figure out the water heater later — you’ll end up with a tub that runs cold.