How to Install a Stiebel Eltron Tempra Plus Tankless Water Heater: 7 Steps an Admin Buyer Actually Learned

Who This Is For (And Why I'm Writing It)

I'm the office administrator who handles equipment purchasing for a mid-sized commercial property management firm. If you're someone who deals with facility upgrades—contractors, wholesalers, installers—this guide is for you. I'm not an electrician or a plumber. But after managing the installation of three Stiebel Eltron Tempra Plus units across our properties in 2024, I've picked up a few things that the manual doesn't spell out.

Let's be honest: the Stiebel Eltron water heater manual is thorough, but it's written for someone who already knows what they're doing. If you're a contractor or a facilities manager installing this for the first time, here's the checklist I wish I'd had. Seven steps, no fluff.

Step 1: Verify Your Electrical Capacity Before You Order

This is the one that trips up almost everyone. The Tempra Plus is a beast. The 24 kW model requires three 40-amp double-pole breakers and 6 AWG copper wire. I can't tell you how many times I've heard, "We'll just swap out the old unit." No, wait—that's exactly what our contractor said before he realized the existing panel didn't have the headroom.

What to do: Have an electrician confirm your service panel can handle the load. And I mean confirm—not "probably."

• Calculate total draw: The 24 kW model pulls about 100 amps at 240V.
• Check if you have 200-amp service minimum. Many older commercial buildings have 100-amp panels.
• Factor in other loads: HVAC, lighting, office equipment.

If I remember correctly, our 2022 install on a building with a 150-amp panel required a sub-panel upgrade. That was an unexpected $1,200. (Should mention: we caught it after ordering the unit, which meant a two-week delay.)

Step 2: Choose the Right Location (Not Wherever the Old Heater Was)

It's tempting to just put the new unit where the old tank was. But the Tempra Plus is smaller and wall-mountable, which means you can put it closer to the point of use. The manual says it can be installed indoors only, and it needs to be protected from freezing. Obvious, right? But I've seen units installed in uninsulated utility closets.

Key considerations:

• Proximity to the main hot water demand. Shorter pipe runs = less heat loss.
• Access to the electrical panel. Running 6 AWG wire 50 feet is expensive.
• Ventilation. It's electric, so no combustion venting, but it still needs airflow for cooling.
• Service access. You'll need to descale it annually. Don't mount it in a corner where you can't reach the front panel.

Pro tip: We installed one in a mechanical room directly below a bathroom cluster. The plumber said it saved about 40 feet of pipe compared to the old location. That translates to faster hot water delivery and less energy waste.

Step 3: Mount the Unit (Level, Please)

The unit comes with a mounting bracket. It's straightforward—mark the studs, drill, screw in the bracket, hang the unit. But here's the detail that our installer nearly skipped: the bracket needs to be dead level. Why? Because the internal flow sensor and heating elements rely on proper orientation. A slightly tilted unit can cause nuisance error codes.

Checklist:

• Use a 24-inch level, not a 6-inch one.
• Confirm the bracket can support 30+ pounds (the unit is heavy when filled with water—about 28 lbs dry).
• Leave at least 12 inches clearance on the bottom for plumbing connections.

Step 4: Install a Thermostat (Wait, Does It Need One?)

This is a common source of confusion. The Tempra Plus doesn't use a standard thermostat like a furnace. It has an internal thermostat that regulates the outlet temperature based on flow rate. You don't need a separate wall thermostat. But—and here's what I learned—if you're installing this as a point-of-use heater, you should consider a mixing valve or a temperature-limiting valve.

Why? The unit can deliver water at 140°F if needed, but for most commercial sinks, you want 120°F max. A mixing valve blends cold water to prevent scalding. Our local code required it for the handwashing sinks in the break rooms.

How to install a thermostat (the real version):

• If you're using the internal controls: Learn the button combination to set the temperature. The manual has a chart. (Should mention: our contractor spent 20 minutes trying to figure out why the water was cold—he hadn't set the temp above the factory default of 104°F.)
• If you want remote control: The unit can be wired to a remote switch or timer, but it's not a standard HVAC thermostat. It uses a low-voltage connection.
• If you need cascading systems: The Tempra Plus can be paired with a flow control system for multi-unit setups. That's a whole other article.

Seriously, read that manual section twice. It'll save you a headache.

Step 5: Connect the Water Lines (Copper vs. PEX)

The unit has 3/4-inch NPT connections. That's standard. You can use copper or PEX, but here's the nuance: the Tempra Plus has a high flow rate—up to 7.5 GPM for the 24 kW model. If you use PEX, make sure it's sized for full flow. A 1/2-inch PEX line will restrict flow and cause the unit to short-cycle.

Installer tip: Use a full-port ball valve on the inlet. We had a contractor use a standard gate valve, and it created enough restriction to cause flow sensor errors. We only caught it because the unit kept displaying an error code.

Don't forget: Install a shut-off valve on the outlet too. Makes descaling way easier.

Step 6: Wire It (Don't Wing This)

I am not an electrician, so I'll keep this brief. But I've watched enough installs to know what matters.

• Use copper wire only. Aluminum is a fire risk at these loads.
• Torque the terminals. Loose connections cause arcing. The manual specifies torque values.
• Each heating element needs its own breaker. The 24 kW model uses three 40-amp breakers. Don't try to combine them.
• Ground it properly. The unit requires a dedicated ground.

Our electrician's advice: "Take pictures of the wiring before you close anything up. Makes troubleshooting later a lot easier." Solid advice.

Step 7: Set the Flow and Temperature (The Final Calibration)

Once everything is connected, turn on the water supply and check for leaks. Then flip the breakers. The unit will go through a self-test cycle.

Initial setup:

1. Turn on a hot water faucet. You want a steady flow, not full blast.
2. The display should show the set temperature and flow rate.
3. Adjust the temperature using the buttons on the front panel. The factory default is 104°F.
4. If the water isn't getting hot enough, check the flow rate on the display. If it's above 4 GPM, the unit may not be able to heat it fully. Reduce the flow slightly.

Common mistake: People set the temperature to 140°F and wonder why their electric bill spikes. For handwashing, 110-120°F is plenty. The unit will cycle less, save energy, and you won't need as much cold water blending.

Final Considerations (What I'd Do Differently)

After three installs, here's what I've learned:

• Always order the service kit upfront. The descaling kit and replacement flow sensor are cheap. Having them on hand saves panic later.
• Don't assume the manual covers everything. The Stiebel Eltron water heater manual is good, but it assumes you know electrical theory. Have a pro double-check your setup.
• Think about hard water. If you're in an area with hard water, budget for annual descaling. A clogged heat exchanger can kill the unit.
• The 'bigger is better' trap. The 24 kW model is powerful, but if you only have a 100-amp panel, it won't work. The 13 kW model might be fine for point-of-use.

The upside of getting it right? Consistent hot water, lower energy costs, and a system that will last 15+ years. The risk of getting it wrong? Expensive callbacks, potential equipment damage, and a very unhappy finance department.

I tell our contractors: this isn't a weekend DIY project for a residential homeowner. It's a commercial-grade install that needs attention to detail. Follow these steps, and you'll be fine. If you get stuck, call a Stiebel Eltron service tech. Seriously. It's cheaper than fixing a mistake.