Stiebel Eltron Hot Water Systems: 8 Questions Installers Actually Ask (And What I've Learned the Hard Way)

If you're an installer or facility manager looking at Stiebel Eltron hot water systems, you've probably got questions. Not the fluffy marketing ones—the real ones. The kind that keep you up at night when a client's tankless unit dies mid-winter.

In my role coordinating emergency hot water replacements for commercial properties, I've fielded hundreds of these. Here are the questions I actually get asked—and the answers I've learned through trial, error, and a few expensive lessons.

1. Is the Stiebel Eltron Tempra 36 Plus worth the premium over cheaper tankless heaters?

Honestly? It depends on what you're optimizing for. If your client just needs hot water and doesn't care about longevity or serviceability, a $400 unit might work for a while.

But here's what I've seen: In Q1 2024 alone, we replaced 7 failed 'budget' tankless units in a single apartment complex. Average lifespan? 18 months. Meanwhile, the Tempra 36 Plus units we installed in 2020 are still running with zero major issues.

The real difference isn't the upfront cost—it's the total cost of ownership. The Tempra 36 Plus has a copper immersion element that's replaceable individually, modulated power control for precise temperature, and German-engineered internals that don't scale up with hard water. I've seen the cost difference recouped in the first 2 years of operation on a 3-bedroom home with two bathrooms.

"I only believed in paying for German engineering after I had to rip out a 'value' unit that was 6 months past warranty and the manufacturer wanted $300 just for the part."

2. How do I drain a Stiebel Eltron hot water heater for maintenance or winterizing?

This is simpler than most installers think—but you need to do it right. I messed this up my first time and ended up with a flooded mechanical room.

Here's the process we use across our 47 units in cold climate installations:

1. Turn off power at the breaker—never drain a tankless with power on. You'll fry the control board.
2. Close the cold water isolation valve (usually a ball valve or gate valve on the inlet).
3. Open a hot water tap somewhere in the building to relieve pressure.
4. Attach a garden hose to the drain port—it's a 3/4" brass fitting on the bottom of the unit.
5. Open the drain valve and let gravity do the work. For the Tempra 36 Plus, there's also a built-in sediment flush plug you can open for a full drain.

Pro tip: If you're in a hard water area, drain and descale every 6-12 months. I've seen units go from 55°C output to 40°C in 18 months just because of calcium buildup. A $25 descaling kit and 2 hours of labor saves a $1,200 replacement.

3. Can I install a Stiebel Eltron heat pump water heater in an existing home without ducting?

It's tempting to think you can just drop a heat pump unit into a basement and it'll work fine. But the oversimplification of 'heat pumps are efficient' ignores the reality of confined spaces.

The Stiebel Eltron heat pump water heaters (like the 80-gallon model) need at least 700 cubic feet of air space around the unit to pull heat from. If you're installing in a 400 ft³ closet, you'll get about 1 cycle per day before the ambient temp drops to 10°C and the electric resistance takes over.

We installed one in a townhouse basement last year—perfect conditions, open to the rest of the basement. The owner saved 62% on their hot water bill. But the next job? A 2×3 meter utility room with no ventilation. Unit spent 80% of its time in resistance mode. Total savings: about 10%.

When I compared the two side by side, I finally understood why Stiebel Eltron recommends a minimum of 2,000 cubic feet for optimal performance. It's not marketing—it's physics.

4. How do I replace the air filter on a Stiebel Eltron unit (or do I need to)?

Good question. Most Stiebel Eltron hot water systems—especially the tankless electric models like the Tempra series—don't have traditional air filters like a furnace would. The air intake is typically through the bottom of the unit, and there's a mesh screen to keep out debris.

But for their heat pump water heaters, yes—there's a filter. Specifically, the air intake filter on the top or side of the unit. It's a washable foam panel, usually around 12" by 18".

Here's the process:

1. Turn off the power at the breaker.
2. Locate the filter access panel (it's usually held by 2-4 screws or clips).
3. Pull the panel out—careful, the foam is fragile when saturated.
4. Rinse the filter under a garden hose (no soap—it'll leave residue).
5. Squeeze out excess water and let it dry completely (I recommend overnight).
6. Reinstall and secure the panel.

When should you replace it? Honestly, you don't need to buy a new one unless the foam is crumbling or deformed. I've seen units go 5 years with quarterly rinses and the filter looked fine. But if you're in a dusty environment (construction site, agricultural area), replace every 2-3 years.

"I skipped air filter maintenance for 3 years on a heat pump install. The efficiency dropped 15% before I figured out why—and the client was not happy."

5. Can I use a Stiebel Eltron unit with a dehumidifier in the same room?

I get this one a lot—especially for basement installations. Short answer: yes, but it's not ideal.

Heat pump water heaters pull heat from the surrounding air. If you're running a dehumidifier in the same space, you're literally fighting the heat pump for the same heat energy. The dehumidifier wants to cool and dry the air; the heat pump wants to warm it up.

We tested this on a job last year—a basement with a Stiebel Eltron heat pump water heater and a Midea dehumidifier running 24/7. The dehumidifier consumed about 500W and the heat pump's COP dropped from 3.2 to 2.1. Net energy loss for the system.

If you need dehumidification (mold risk, musty smell), a better strategy is to ventilate the space with outdoor air or use a dedicated dehumidifier that's controlled by a humidistat and shuts off when the heat pump is running.

6. What's the real-world cost difference between a Stiebel Eltron tankless and a traditional tank heater?

I'll be transparent: the upfront cost is higher. A Tempra 36 Plus retails around $1,200-1,400, plus installation. A 50-gallon tank might be $500-700 installed.

But here's the math that changed our company's recommendation policy in 2023:

On a typical 3-person household with electric tank heater ($0.12/kWh):

• Tank: 4,500 kWh/year × $0.12 = $540/year
• Tempra 36 Plus: 3,200 kWh/year × $0.12 = $384/year
• Annual savings: $156
• Break-even: ~5 years

But that's assuming the tank lasts. If the tank fails at year 8 (which is common in hard water), you're looking at $700 replacement plus labor. The Tempra 36 Plus has a 10-year warranty on the heat exchanger and a 5-year parts warranty. We've had units in service for 12+ years without needing replacement.

The total cost of ownership over 10 years heavily favors the tankless—but only if you factor in longevity and energy savings. The vendor who lists all fees upfront—even if the total looks higher—usually costs less in the end.

7. What maintenance does a Stiebel Eltron tankless actually need?

Less than you think. More than you want.

Here's the minimized maintenance schedule I recommend after 200+ installations:

• Every 6 months: Flush the unit with a descaling solution (we use a 50/50 vinegar-water mix or a commercial descaler). Takes 30 minutes with the built-in flush ports.
• Annually: Inspect the inlet filter screen for debris, check the temperature sensor accuracy, and verify the flow sensor is clean.
• Every 2-3 years: Replace the anode rod (if your unit has one—some newer models have a self-cleaning feature).

I knew I should do annual descaling, but thought "what are the odds" of scaling in my area with moderately hard water. Well, the odds caught up with me when I had to replace a flow sensor that cost $180 because calcium buildup seized the impeller. That was the year I started recommending biannual descaling to every client.

8. Why does my Stiebel Eltron unit show an error code, and what do I do?

Error codes are the bane of every installer's existence. But for Stiebel Eltron, they're actually helpful once you know the language.

The most common codes I see on the Tempra 36 Plus:

• E1/E2: Temperature sensor issue. Usually a loose connection or faulty sensor. Check the wiring at the control board and at the sensor.
• E3/E6: Flow sensor problem. Debris stuck in the impeller or a dead sensor. Flush the unit and clean the flow sensor chamber.
• E4: Overheat protection. The unit detected outlet water above 85°C. Usually caused by low flow (clogged inlet filter or partially closed valve) or a bad flow sensor.
• E7: Ground fault. This one scares people, but it's often a grounding issue in the building wiring—not the unit itself. Test the ground continuity and clean the connections.

My rule: always check the inlet filter first before replacing parts. I've seen dozens of calls where a technician replaced a $200 flow sensor when the $2 inlet filter was just clogged with construction debris. Saved the client $198 and 45 minutes of labor.