What Temperature Should I Set My Water Heater for a Walk-In Tub?

The Ella manuals and spec sheets do not print a thermostat setting for your home water heater. The temperature they do specify is the bath itself: the manuals warn that water above 100.4 degrees Fahrenheit may be harmful, so the number that matters is the hot and cold mix you set at the faucet or thermostatic valve before the water reaches you. Your water heater's job is to deliver enough hot water, at a high enough flow, for the fast-fill faucet to fill the tub while you sit in it, which is why heater size and flow get more attention than the dial. How do you fill a walk-in tub after you get in? covers the fill sequence, and this page explains where the temperature is set, what the tub's own heater does and does not do, and how to tell whether your water heater is up to the job.

Where the Bath Temperature Is Actually Set

In a walk-in tub you are seated with the door locked before the water arrives, so the temperature has to be right at the spout from the first gallon. On the dual-lever 5-piece fast-fill faucet and the 2-piece fast-fill faucet, neither of which is thermostatic, you set the mix by hand with the levers before the water reaches you. That is the step the first-bath sequence places ahead of opening the faucet, and it is the point where the 100.4 degree limit applies.

Tubs ordered with an Ella thermostatic faucet package include a Thermostatic Control Valve, or TCV, on the deck. It blends hot and cold to a set temperature before the water leaves the faucet, factory-set at 100.4 degrees Fahrenheit, and it limits the hot flow if the cold supply drops. That matters more in a walk-in tub than in a shower, because you cannot step out of the way of a temperature spike until the tub drains. The valve can be adjusted for warmer water: the first video shows removing the set screw cover, loosening the set screw with an Allen wrench, resetting the handle a quarter turn counterclockwise and confirming the spring-loaded anti-scald button is set before tightening the screw again. The valve carries a 1-year limited warranty, separate from the lifetime parts warranty, and it needs an inline filter or mesh on the supply lines because a cartridge fouled by calcium or iron is not covered. What Is a Thermostatic Control Valve (TCV) on a Walk-In Tub? explains the valve in full.

What the Tub's Own Heater Does and Does Not Do

Many owners assume the in-line water heater under the tub will bring cool water up to temperature. It will not. The in-line heater is plumbed into the hydro massage loop and maintains, but does not raise, the bath temperature while the hydro pump is running. Your home water heater does the heating. The in-line heater only offsets the natural cooling of the bath once the water is above the highest jets and the hydro massage is on. It switches on and off with the pump, so there is no heater button and no thermostat to set, and it does nothing for the air massage, which has no heater. On tubs with independent foot massage, such as the Ultimate, the heater sits on the foot massage loop, so running the foot jets is what keeps the water warm.

The spec sheets rate the heater at 6A 650W on the Standard, Zen and Flow, 5.5A 650W on the Elite and Petite, and 9A 1000W on the Ultimate foot loop. Those ratings hold a temperature; they do not create one. A bath filled with lukewarm water because the house heater ran short stays lukewarm, which is the practical reason to get the fill right at the source. The second video shows the heater working with the water pump to keep the temperature you set at the faucet. What Is an In-Line Water Heater on a Walk-In Tub? covers the heater, its unions and its warranty.

Why Heater Size and Flow Matter More Than the Dial

The Ella faucet fills at about 16 gallons per minute, and you typically use 30 to 75 gallons per bath once you are seated, because your body displaces part of the volume. A tank heater supplies stored hot water at any flow rate until the stored water is used up, so an undersized tank runs out partway through the fill and the last part of the bath arrives cold. A tankless heater never runs out, but it can only warm so many gallons per minute, so an undersized unit delivers the whole fill cooler than the temperature you set. The support team's guidance is a tankless unit rated for at least 11 gallons per minute, and its own example is a 27 kW unit rated at 4.8 gallons per minute that struggles to keep up with the fast-fill faucet.

For you, the difference is in how a shortfall shows up. If the bath starts warm and turns cold before the water reaches the jets, the tank is too small or another fixture was running at the same time. If the water is cooler than you set from the first minute, a tankless unit is being asked to heat faster than it can. Neither is fixed by the tub's in-line heater, and neither is fixed by pushing the faucet levers hotter, because the supply itself is the limit. Does a tankless water heater work with an Ella walk-in tub? has the checks to run before the tub arrives.

Cold Air at the Jets Is Not a Water Temperature Problem

If the water feels right but the air massage feels cold, the water heater is not the cause. The air pump has no heating element and draws its supply from the space under the tub, so a cold floor or an unheated space beneath the tub means cooler air at the jets. The motor warms as it runs, warming the bathroom first helps, and running the hydro jets so the in-line heater maintains the water temperature offsets the feel of the moving air. Why Does the Air Massage Blow Cold Air? There Is No Heating Element explains why this is normal operation.

Putting It Together for Your Bathroom

• Plan the water heater by the tank size or tankless flow figure for your model, not by its thermostat.
• Set the bath temperature at the faucet levers or the TCV before the water reaches you, and keep the bath at or below 100.4 degrees Fahrenheit.
• Fit and periodically clean the inline filter or mesh if your tub has a TCV.
• Expect the in-line heater to hold the temperature you filled at, not to raise it.
• Avoid running other hot water fixtures during the fill, since they draw from the same supply.

If you are not sure which faucet package or heater your tub has, check your order confirmation or look on the deck for a separate temperature handle beside the faucet, then ask your Ella dealer or the team at (800) 480-6850.

Watch: Ella's Bubbles: In-line Water Heater Maintains Comfortable Water Temperature with chapters and a full transcript.

Related Guides

• What Size Water Heater Do I Need for My Walk-in Tub?
• Why Does My Hot Water Run Out Before the Tub Is Full?
• How Do I Adjust the Maximum Temperature on a Walk-In Tub Thermostatic Valve?

Related Videos

Common Questions