Stiebel Eltron FAQ: Wall Heaters, Tempra 29 Plus & Heat Pump Disadvantages — Answered by a Service Tech

I'm a field service technician at a regional HVAC company. I've handled 400+ emergency no-heat and no-hot-water calls in nine years—including same-day repairs for apartment buildings and a Christmas Day rescue when a family's water heater died mid-holiday. These are the questions I actually answer on those calls, and the answers you need before you pick up the phone.

1. What are the disadvantages of a heat pump?

Let me be straight with you, because I sell and install heat pumps. They're genuinely efficient, but they're not magic boxes. Four things catch people off guard:

• The heat feels 'gentle,' not hot. If you're coming from a gas furnace or electric resistance heat, a heat pump's airflow can feel lukewarm—especially on a January morning. It takes longer to bring a cold room up to temperature, and that surprises people.
• Install quality is make-or-break. A heat pump is not a drop-in replacement. Load calculation, refrigerant lines, condensate drain—if any of it's wrong, you'll be cold for years. And fixing it after the fact is expensive.
• Cold weather cuts into output and efficiency. Below about 10°F, most heat pumps start losing power. The good ones still heat, but they work a lot harder.
• Upfront cost is real. Expect roughly $4,000–9,000 installed, ballpark, though the 30% federal credit (up to $2,000 for qualifying heat pumps; energy.gov, January 2025) helps.

I have mixed feelings. Part of me loves how clean and efficient they are. Another part has been called back too many times to fix a bad install—and watched the customer blame the equipment. Last winter, during a -15°F cold snap, we ran 47 emergency calls in one week, and half of them involved heat pumps that were undersized or poorly installed. The technology isn't the problem. The gap between what the salesperson promised and what the house needed is.

2. Is the Stiebel Eltron Tempra 29 Plus tankless water heater worth the price?

The Tempra 29 Plus is the unit I recommend when a customer needs a whole-house electric tankless. But 'worth the price' depends on what you're comparing it to.

The unit itself lists for roughly $400–700 depending on the retailer (publicly listed prices, checked January 2025). That's more than budget tankless units, but the difference shows in the build: individually replaceable heating elements, and better resistance to hard water damage.

The cost people miss is the electrical work. The Tempra 29 Plus is a 29 kW unit—roughly 120 amps at full load. That's a serious electrical demand. If your panel has room, budget $500–1,500 for wiring (regional estimates, 2025). If it doesn't, you might be looking at a service upgrade that costs more than the heater. That's why I've learned to ask what's not included before I ask the price.

And the honest tech take: I only believed the Tempra's quality after replacing elements twice on a cheaper unit I'd recommended to save someone money. It failed again within a year. The Tempra in the same house never needed a call. I do not say that often.

3. Stiebel Eltron wall heater thermostat replacement: How do I know if the thermostat is actually the problem?

Before you replace anything, run the 10-minute diagnostic. I say this from experience.

I knew I should check the breaker and the heater's thermal cutout before assuming a thermostat was dead. But it was a Friday, I was exhausted, and I thought 'what are the odds?' The odds caught up with me. I replaced a perfectly good thermostat and invoiced a customer for a part they didn't need. I refunded it when I found the actual problem twenty minutes later: a tripped breaker.

Don't repeat my mistake. Check in this order:

1. Power first. A tripped breaker, blown fuse, or a GFCI that's off makes a working thermostat look dead. Test the heater with a meter, not the switch.
2. The thermal cutout (that small reset button near the bottom). If it tripped, the heater behaves like it's dead.
3. The click test. Turn the thermostat well past the room temperature. If it clicks but no heat comes, the thermostat contacts are likely fine—suspect the heating element. If no click at all, the thermostat is probably worn.

If you do need a thermostat, the part is $30–60 (parts distributor listings, January 2025), and a service call to install it runs $150–350 depending on where you live. Bottom line: the thermostat is a logical suspect, but check power before you spend money on parts. And if a tech quotes a thermostat replacement without checking power first, that's a red flag.

4. Can a Stiebel Eltron wall heater work as a garage heater?

Yes, if you size it honestly—and most people don't.

The rule of thumb: about 10 watts per square foot for a reasonably insulated garage. A typical 2-car garage is around 400 sq ft, so you're looking at roughly 4,000W. A single Stiebel Eltron CK 20 (2,000W) covers about half of that. You'd need two units, or to adjust your expectations.

Uninsulated garage? Double the wattage. There's no way around physics—you'll just be heating the outside.

Clearance matters too. The heater needs proper distance from the floor and a clear space in front of it. I almost mounted my first garage heater directly under the breaker panel. Double-checking the manual beforehand saved me a code violation—and a very different kind of inspection. So glad I read that page.

And check with your local building office before buying. Some cities have specific rules for garage heater installations. It's easier to adjust the plan on paper than after the heater is bolted to the wall.

5. How long do Stiebel Eltron products last?

Based on what I see in the field—not marketing materials—wall heaters and tankless water heaters typically run 15-20 years. Big caveat: the things that wear out are thermostat contacts and heating elements, especially with hard water or constant use.

When should you repair versus replace? Here's the math I use with customers:

• First repair on a unit under 8 years old: repair it.
• Second repair on a unit over 12 years old: replace it.

Replacement elements run $40–80. A new wall heater or tankless unit is $400–700. When you add a service call on top of that, a second repair on an older unit is usually the no-brainer. I'll tell you that even though it means less work for me.

(note to self: I really should print this on the service report template.)

6. Why does my tankless water heater run warm instead of hot in winter?

This is the question nobody asks—until they're standing in a lukewarm shower in January. It should be asked before the purchase.

A tankless heater has a fixed heating capacity. The Stiebel Eltron Tempra 29 Plus, for example, can raise incoming water by about 65°F at 3 gallons per minute (manual spec, not the sales brochure). In summer, with groundwater at 60–70°F, you get 125–135°F at the tap. Plenty. In winter, northern groundwater can drop to 40–45°F, and the same flow produces only 105–110°F. Warm, not hot.

If you drop the flow to 2 GPM, the temperature climbs back above 130°F. That's the trade-off of every tankless unit. Know your incoming groundwater temperature before you buy—it saves a lot of cold-shower surprises.

7. What's the most common emergency call for Stiebel Eltron units?

The honest answer: about a third of the time, it's not the unit. I've responded to plenty of emergency calls where the heater was fine—but the breaker was tripped, a connection was loose, or the circuit was undersized. The heater wasn't dead. It was starving.

When the unit itself is the problem, it's usually one of two things: the heating element in hard-water areas, or worn thermostat contacts. Both are normal wear items. Both are replaceable. A truly dead unit is rare, and usually follows years of ignored maintenance or a DIY install gone wrong.

So here's the advice I give on every call: when the heat dies, check the cheap stuff first. Breaker, reset button, thermostat. Then call a tech. Take it from someone who replaced a perfectly good thermostat once. I'm still embarrassed.