Heated seat, heated backrest and inline heater: how a walk-in tub keeps you warm

Why do people get cold in a walk-in tub?

A walk-in tub changes the order of a bath. In a regular tub you fill first and then climb in. In a walk-in tub you step through the door, close it, sit down and then fill, because the water would pour out of an open door. At the end the order flips again: the water holds the door against its seal, so you stay seated until the tub has drained. That gives every bath two stretches where you sit with little or no warm water around you: the fill and the drain.

How long those stretches last depends on the tub and your plumbing. The Ella’s Bubbles Companion holds 65 to 85 gallons with a bather inside, and its fast-fill faucet is rated for up to 16 gallons a minute at 60 psi under ideal home plumbing, according to its spec sheet. At that rate, 60 gallons arrives in under four minutes. At a more typical 7 gallons a minute it takes more than eight. A full walk-in tub typically takes up to about seven minutes to drain, according to a U.S. patent for a faster tub drain, and longer with a slow house drain; our fill and drain time guide shows how to time your own.

That matters more for older bathers. The National Institute on Aging says changes that come with aging can make it harder to notice when your body is getting too cold. It advises keeping the home at at least 68°F and warns that even mildly cool rooms of 60 to 65°F can lead to hypothermia in older adults. It also lists diabetes, thyroid problems, Parkinson’s disease, arthritis and some medicines among the things that make it harder to stay warm. A wet body in a cool bathroom loses heat quickly, which is why “I got cold waiting for it to drain” is one of the most common walk-in tub complaints. The main site lists it among the real walk-in tub problems and how to avoid each.

What does a heated seat and backrest do?

A heated seat and backrest is a set of low-voltage heating pads built into the tub shell behind the seat and the back wall. It warms the surfaces your body touches, so you are not sitting on cool acrylic while the tub fills, and it keeps working after the water has gone.

The Ella owner’s manual describes how its surface heater control works:

• Switch it on 5 to 10 minutes before you get in. The manual recommends this so the seat is already warm when you sit down.
• One press starts a 30-minute timer. A red light shows that the heaters are running. Press the button again to turn them off sooner.
• It reaches a comfortable level within 5 to 10 minutes.
• It is a small load. The controller plugs into a 120-volt, 15-amp GFCI supply, sends 24-volt DC power to the pads, and lists a 96-watt maximum heater load.

On the Ella Companion and Escape spec sheets, the heated seat and backrest appears under optional features. That is the practical lesson: decide on it when you order, and check that it is written into your quote. Our therapy options builder shows how it fits with jets and the other add-ons.

What does an inline heater do, and what can’t it do?

An inline heater sits in the plumbing of the water-jet system. As the pump circulates bath water through the jets, the heater warms it a little on each pass, which slows the natural cooling of the bath. On the Companion and Escape sheets it is rated at 5.5 amps and 650 watts and is listed with the hydro massage (water-jet) system.

The limit is simple physics. The U.S. Energy Information Administration defines a Btu as the heat needed to raise one pound of water by 1°F, and one kilowatt-hour equals 3,412 Btu. Sixty gallons of water weighs about 500 pounds, at the 8.34 pounds per gallon the U.S. Geological Survey uses. Running a 650-watt heater for a full hour delivers 0.65 kWh, or about 2,218 Btu. Spread over 500 pounds of water, that is a rise of about 4.4°F per hour, and that is the best case with no heat escaping into the air, the tub or you.

So an inline heater is a keep-warm device. It helps a 20-minute soak end close to where it started, but it cannot rescue a lukewarm fill, and it does nothing during the fill or the drain because the jets are not running then. The temperature you fill at is the temperature you get. That makes your home’s hot water supply the real heater; the main site’s water heater sizing guide covers whether yours can keep up.

Which feature warms which part of the bath?

The hand-shower figure comes from the faucet section of the Companion sheet. If your plan is a tub with a shower for the drain wait, our sister site walks through it in drain time and the wet-seat wait.

How warm is too warm?

Heat helps comfort only up to a point. The Ella manual warns that water above 100.4°F (38°C) may be harmful, tells anyone with a heart condition or who takes medicines, herbal remedies or sleep aids to ask a physician first, and warns that staying in a heated bath too long can cause hyperthermia, with dizziness, drowsiness and fainting. The Arthritis Foundation describes 92 to 100°F as a healthy soaking range, and the U.S. Consumer Product Safety Commission sets 104°F as the most a spa should ever reach.

Three habits keep warmth safe:

1. Measure, don’t guess. Hands are poor thermometers, especially with diabetes or nerve damage. A floating bath thermometer costs a few dollars. Our arthritis guide has a thermometer check.
2. Warm the room, not just the water. A heated seat cannot offset a 60°F bathroom. If you need extra heat, the NIA cautions that some portable space heaters are fire or carbon monoxide hazards; keep any heater well away from water, and ask an electrician about a permanent bathroom heater.
3. Stand slowly. A warm soak can leave you lightheaded. Use the grab bar, and sit a moment after the tub drains before you open the door. Our page on who should skip jets covers blood pressure that drops on standing.

Is a heated seat worth it?

For most bathers who feel the cold, we think it is one of the best-value options, for three reasons. It covers all three phases of the bath, including the drain, where nothing else helps. It costs almost nothing to run: a full 30-minute cycle at the 96-watt maximum uses about 0.05 kWh, under one cent at the July 2026 U.S. average of 18.31 cents per kWh. And it has no jets to clean. The inline heater is worth having if you plan long soaks with the water jets, but it is a partner to the jets, not a substitute for a hot fill or a warm room.

If cost is the deciding factor, put warmth before jet count. A tub with a heated seat, a fast-fill faucet and a good drain often feels better day to day than one with more jets and a slow, chilly drain. The operating cost calculator shows that hot water, not the motors, is the real running cost.

Always cold in the bath? Tell us about your bathroom and water heater. Aging Safely Baths will suggest models with heated surfaces, fast fill and fast drain, and quote them in writing. BBB accredited, helping families since 2012.

Sources

• Ella acrylic walk-in bathtubs owner’s manual (rev. 03/18): surface heater operation (5 to 10 minutes, 30-minute timer), 96 W maximum load on a 120 V 15 A GFCI supply, 100.4°F and hyperthermia warnings.
• Ella’s Bubbles Companion and Escape spec sheets (PDF): inline heater 5.5 A / 650 W, optional heated seat and backrest, occupied capacity, 16 GPM faucet at 60 psi, 1.9 GPM hand shower.
• National Institute on Aging, Cold weather safety for older adults (updated January 26, 2026): 68°F minimum, 60 to 65°F hypothermia risk, conditions and medicines, space heater cautions.
• U.S. Energy Information Administration, British thermal units (Btu definition; 1 kWh = 3,412 Btu) and Electric Power Monthly Table 5.6.A (18.31¢/kWh, July 2026).
• U.S. Patent 8,549,678, Accelerated tub drain (background: walk-in tub volumes “require up to seven minutes to drain”).
• U.S. Geological Survey, A million gallons of water: how much is it? (8.34 pounds per gallon).
• Arthritis Foundation, Heat therapy helps relax stiff joints (92 to 100°F); CPSC, CPSC warns of hot tub temperatures (104°F maximum).

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