What water temperature does the in-line heater hold during hydro massage?

The in-line heater does not hold a fixed, published temperature. It maintains whatever temperature you set at the faucet when you filled the tub, and it does that only while the hydro massage pump is running, because it has no thermostat to set and no button of its own. What Is an In-Line Water Heater on a Walk-In Tub? describes the part itself; this page covers what temperature you can expect, what actually decides it, and the 100.4 degree Fahrenheit ceiling Ella recommends for bath water.

There Is No Set Point, Only Your Fill Temperature

People often expect a hot tub style heater with a dial and a target number. An Ella in-line heater works differently. It sits in the hydro massage loop under the tub, and when the hydro pump pulls water through the jets, that water passes through the heater and back out. The heater offsets the natural cooling of the bath so the water stays close to where it started. It switches on and off with the pump, so there is nothing to program and nothing to adjust. The temperature it holds is the temperature you chose at the faucet, whatever that was.

The short video on this page states the same thing in one sentence: with the five-piece or two-piece fast-fill faucet set you set the temperature at a level that suits you, and when you engage the hydro massage the in-line heater, working with the water pump, maintains a consistent warm temperature. Two things follow from that. The heater will never raise a bath that arrived cool, and it will not keep a bath warm while you soak with the hydro switched off.

What Actually Decides the Temperature of Your Bath

Because the heater only maintains, your bath temperature is decided before the tub is full, by three things.

1. Your home water heater. Depending on the model, a walk-in tub takes roughly 55 to 75 gallons or more to fill once you are seated. A Transfer60 takes 55 to 75 gallons depending on the bather, and the Big4One holds 127 gallons unoccupied and 75 to 100 gallons occupied. Ella recommends a 75 gallon or larger tank, or a tankless unit rated around 11 gallons per minute; a 40 gallon tank can work only if nothing else draws hot water at the same time. If the hot water runs out halfway through the fill, Why Does My Hot Water Run Out Before the Tub Is Full? covers tank sizing and 3/4 inch supply lines.
2. The faucet setting. Fill hot from the faucet to the level you want. On a tub with the Ella thermostatic control valve, the handle has a spring-loaded anti-scald pin that stops at 100.4 degrees, and the button must be pushed to go hotter. The second video shows how that stop works and how the valve is internally adjusted with an Allen wrench; that adjustment is a job for your plumber, not a routine setting.
3. The room. Cold bathroom air and a poorly insulated room are things the heater has to work against, and they are listed among the likely causes when water seems to cool faster than expected.

Ella's published guidance is to keep bath water at or below 100.4 degrees Fahrenheit. That figure is the practical ceiling for a hydro session, and it matches the anti-scald stop on the thermostatic valve. So while there is no held temperature printed on a spec sheet, the range you should expect is simply your comfortable fill temperature, up to that ceiling, held steady for as long as the hydro runs.

When the Heater Runs and When It Does Not

• It runs only with the hydro pump. There is no heater switch. Fill the tub until the water is 2 inches above the highest jets, switch on the hydro massage, and the heater comes on with the pump.
• On tubs with independent foot massage, the heater is attached to the foot massage pump. On a Hydro plus Hydro Foot build, the seat jets alone will not hold the temperature; run the foot jets. What Is Independent Foot Massage on a Walk-In Tub? explains that layout and the foot-only fill level.
• It does nothing for the air massage, which has no heater. On an air plus hydro tub, air alone does not keep the water warm.
• Soaking tubs and air-only tubs have no hydro pump and no in-line heater, and the heater cannot be added to those configurations.
• With the hydro off, the water cools like any bath. That is expected and not a fault.

Do Walk-In Tubs Have Heaters to Keep the Water Warm? puts the same routine in one line: fill hot from the faucet, then run the hydro massage to hold that warmth for the rest of your bath.

Heater Ratings on the Spec Sheets

The heater is a modest electrical load, which is another reason it maintains rather than heats. The published ratings are 6A 650W on the Standard, Zen and Flow, 5.5A 650W on the Elite and Petite, and 9A 1000W on the Ultimate foot loop. Like the pumps and controls, the heater is ETL certified, clearly marked, and placed where an electrician can reach it during installation. It is covered as supporting equipment under the Lifetime Limited Warranty, alongside the pumps and electronic controls.

If the Water Still Cools During a Hydro Session

Work through these in order before opening a ticket.

1. Confirm the fill was hot. The heater cannot raise a cool fill, and if the fill itself is not hot enough the house supply is the place to look.
2. Confirm the hydro pump is running for the whole session, and on a Hydro plus Hydro Foot tub that the foot pump is running.
3. Confirm the package. Soaker and air-only tubs have no heater.
4. Check the heater cord at the control box. A heater plugged into the wrong port never runs. If the heater and the lights stopped working together, check the green LED on the box and the GFCI.
5. Look for water at the heater unions. The usual cause is an over-tightened or displaced O-ring; the union is taken apart, the O-ring reseated and the union reassembled, and the heater threads should match the pipe threads.

If you fill hot, the hydro runs, the cords are on the right ports and the water still drops noticeably during a session, open a ticket at ellasbubbles.com/support or call your Ella dealer or the team at (800) 480-6850. Include your model, serial number, therapy package and a photo of the control box with every cord visible. Ella does not send technicians; if a part is needed it ships under the warranty and a local licensed plumber or electrician fits it. Why Doesn't the Water Stay Hot and Why Do the Jets Blow Cold? is the full troubleshooting page.

Related Guides

• What Size Water Heater Do I Need for My Walk-in Tub?
• Does My Ella Tub Include an In-Line Heater? Hydro, Air-Only, Soaker and Clearance Units
• The Thermostatic Control Valve (Anti-Scald): Which Faucets Have It, Its Setting, and Water-Heater Advice

Common Questions