Stiebel Eltron Tempra Plus vs. Stiebel Eltron Solar Water Heater: A Contractor's Honest Comparison

I've been ordering and installing water heating equipment for eight years. In that time I've made enough expensive mistakes to fill a small binder—and I update it after every job. So when a customer asks me to compare the Stiebel Eltron tankless water heater Tempra Plus with a Stiebel Eltron solar water heater, I don't start with marketing specs. I start with four questions: What's the budget? How is the building used? What's the electric service like? And who's going to maintain it?

I'm not an engineer, and I do not pretend to have every answer. My experience is mostly residential and light commercial. If you're designing a 40-unit apartment building, call an engineer. But if you're a contractor or facility manager trying to choose between two solid Stiebel Eltron systems, this comparison should help.

The Comparison Framework

Here's the framework I use: real installed cost, monthly operating cost, installation pain, and maintenance pain. Most conversations stop at efficiency and forget the rest. That's a mistake.

Dimension 1: Real Installed Cost

If I remember correctly, the Tempra Plus 24 was around $840 from my distributor in early 2024. Actually, it might have been $890—don't quote me on the exact number. The point is the equipment cost is low enough for a small customer to say yes.

The real cost is the wire. An electric tankless water heater is power hungry. The Tempra Plus needs a dedicated circuit and enough feeder capacity. On a 2018 job, I quoted a customer a Tempra Plus without checking their 100-amp service. We got to the site and the panel was full. The upgrade added $1,200 to a job the customer had approved at $2,300. I paid for that one with my credibility. Lesson: price the panel before you price the heater.

A Stiebel Eltron solar water heater is a different beast. For a two-collector system on jobs I priced in the Northeast, I've seen installed quotes from $4,500 to $8,000. That's not because the brand charges a premium—you're buying more parts: collectors, a storage tank, a solar station, an expansion vessel, and glycol.

The small customer's first reaction is usually sticker shock. But here's something that changes the conversation: according to energy.gov (accessed January 2025), qualified solar water heating systems may be eligible for the federal Residential Clean Energy Credit. I'm not a tax advisor, and you should verify current IRS rules before quoting. But don't dismiss solar just because the initial number is higher.

Dimension 2: Operating Costs and Efficiency

This is the dimension where solar usually wins. According to energy.gov (accessed January 2025), tankless water heaters can be 8–34% more efficient than storage tank water heaters because they don't have standby losses. The Tempra Plus also modulates output in small increments, according to Stiebel Eltron's published specs, which helps hold the outlet temperature steady.

Solar water heaters can reduce water heating bills by 50–80%, also according to energy.gov. In my experience, that number holds best for customers with good southern exposure. In a cloudy winter climate, the solar collector still helps, but the backup heater carries the load.

When I compared the two side by side on a customer project in 2022—same water usage, one with the Tempra Plus, one with solar—I finally understood something. The real comparison isn't efficiency. It's the cost of a reliable supply of hot water in a specific home. If your customer pays $0.09/kWh, the solar payback is slow. If they pay $0.30/kWh, solar becomes a much easier conversation.

Dimension 3: Installation Complexity and Space

The Tempra Plus is compact. It mounts on a wall and leaves room for a vacuum cleaner or a rack of towels. But "compact" does not mean "quick." You still need to verify the electrical service and choose the right model for the flow rate. Don't spec a 13 kW model for a house with two showers and expect a happy customer. Actually, check the flow rate first—that's exactly the kind of mistake I made in my first year.

Solar is more than an appliance. It's a system with collectors, a storage tank, piping, and controls. If you do not have roof space or a place to put the tank, the conversation ends there. On a 2019 job, I forgot to order the solar station along with the collectors. The collectors sat in a warehouse for three days while we paid freight and lost a week. That mistake is still in my checklist.

What most people don't realize is that solar quotes can exclude the little parts that make the system work. I've seen a quote without mounting rails and another without the expansion vessel. Ask for a complete list before you commit.

Dimension 4: Maintenance and Winterization

Here's something vendors won't tell you on a product page: both systems need maintenance. The Tempra Plus needs periodic descaling, especially in hard water. Solar systems need fluid checks, pressure checks, and sometimes a glycol top-up.

I learned that lesson the hard way in November 2022. A customer had a ground-mounted solar collector. I used an electric leaf blower to clear dry leaves off it, and that was fine. Then it snowed. An electric leaf blower is useless on wet snow. I briefly thought about using an electric snow blower to clear a path, but the unit was too close to the collector—I would have thrown gravel into the glass.

What I actually needed was to winterize the loop before the weather turned. And I didn't know how to use an air compressor properly. I'd used my compressor for nail guns and truck tires, but not for water lines. Here's the short version: set the regulator to around 20–25 psi, connect the hose to the drain port, open the isolation valve, and blow the water out until it runs clear. Do not open it at 90 psi and hope for the best.

I learned that last part after cracking a brazed joint on a customer's solar loop. The repair cost $300 plus a weekend with no hot water. I only believed in low pressure after I ignored it and paid for the lesson.

Which One Should You Recommend?

If I'm working on a small bathroom addition, a rental unit, or a customer on a strict budget, I ask: does the electric service have room? If yes, the Stiebel Eltron tankless water heater Tempra Plus is often the right call. It's a dependable piece of German engineering, and it's the easier system for a small contractor to order, install, and support.

If the customer has good solar exposure, is thinking about long-term energy costs, and can handle the upfront number, I recommend the Stiebel Eltron solar water heater—but only after an honest conversation about maintenance. Put another way: solar gives you lower utility bills, but it also gives you to-do lists.

I don't think one is universally better. The Tempra Plus is the safer default. Solar is the better long-term bet in the right situation. And if you're a small operation, don't let a distributor act like you're a nuisance for ordering one unit. I've been that person with the $300 order, and the distributors who treated it seriously are the ones I still call for bigger projects. Today's small order can be next year's annual maintenance contract.