Building a Sustainable Hot Water System for 6 Units: A Procurement Manager’s Real Project Notes

It Started with a Phone Call and a Spreadsheet

I’m a procurement manager at a 40-person property management company. I’ve managed our HVAC budget—about $180,000 annually—for 6 years now, negotiated with 15+ vendors, and I’ve documented every single line item in our cost tracking system. When my boss called me in Q2 2024 and said, “We’re converting the Grove Street building from a gas boiler to electric, and we need tankless water heaters for six units,” I knew it wasn’t just another order.

It was a chance to rethink how we did things. The old system? A massive boiler feeding a shared storage tank. Expensive to maintain, inefficient in summer, and let’s just say the tenants weren’t thrilled with “shower roulette.”

I built a rough cost model in 2 hours. My first estimate: $4,200 per unit for equipment and install, give or take. But I knew from experience—tracking 700+ orders over those 6 years—that the “give or take” part was where the real story lives.

The Hunt: Why I Almost Went with a “One-Stop” Vendor

I reached out to 5 vendors. One of them—let’s call them the “Comfort Solution” company—offered a package deal: equipment, installation, and a 2-year warranty for $4,800 per unit. Sounded reasonable. But I’ve been burned by bundles before. Remember that time I skipped a detailed review because “it’s basically the same as last time”? $650 mistake, right there (note to self: always at least skim the fine print).

I started digging. The Comfort Solution bundle used a mid-range “EcoHeat” unit, not a Stiebel Eltron. I’ve used Stiebel Eltron before—specifically the Tempra 29 Plus—for a smaller 2-unit project back in 2022. That unit (this was back in 2022, before things went wild) was a workhorse. I didn’t need to field a single callback about hot water. But this time, I needed 6 units, and I needed to be 100% sure about the specs.

Here’s what I found about the Stiebel Eltron Tempra 29 Plus kw rating:

The unit pulls 27 kW at 240V. That’s about 112 amps dedicated. In a 6-unit building, that’s a lot of load. I called a master electrician friend of mine (we’ve worked together on 12 projects), and he said, “You need a 300-amp service upgrade for the building. That’s another $3,000 – $4,000.” Suddenly, the “cheap” bundle didn’t look so cheap.

Industry standard for tankless water heaters: For a 40°F (22°C) temperature rise, you need approximately 4.5 kW per GPM. At 27 kW, the Tempra 29 Plus delivers about 6 GPM. That’s enough for 2 simultaneous showers in a single unit, but for 6 units, that’s 6 separate units.

The Plot Twist: When “Standard” Wasn’t Standard

The surprise wasn’t the electrical load. It was the pipe sizing.

I called Stiebel Eltron’s tech support—they’re based in Massachusetts, and I’ve used their helpline 3 times in 2 years. The rep said, “The Tempra 29 Plus requires 3/4-inch NPT connections. If you’ve got a half-inch line feeding the unit, you’ll lose flow, and the unit will cycle or underperform.”

Sure enough, the Grove Street building’s original plumbing was a mix of 3/4-inch and 1/2-inch. Not a huge deal, but it meant running new supply lines for each unit. I factored that into my TCO spreadsheet: +$600 per unit for new copper and labor.

I have mixed feelings about this. On one hand, I was annoyed at the extra cost. On the other hand, it’s the right thing to do. A properly sized pipe ensures the unit meets its rated kw rating. If you starve it, you’re basically paying for 27 kW and getting 18 kW performance. That’s a $1,200 mistake (not to mention cold showers).

So now my cost model looked like this per unit:

• Stiebel Eltron Tempra 29 Plus: $1,450 (as of Fall 2024, actual street price from a wholesaler I use)
• Electrical (service upgrade + breakers + 6/2 AWG wire): $1,200 average
• Plumbing (new 3/4-in lines + fittings): $600
• Misc (mounting, T&P valve, permits): $300
• Labor (plumber + electrician): $1,000
• Total per unit: $4,550

Compare that to the Comfort Solution bundle at $4,800 with a lower-tier unit. Not only was I saving $250 per unit, I was getting German engineering and a track record of reliability I’ve seen firsthand.

The Moment of Truth: Installation Week

Week 3 of the project. The electrician finished the service upgrade (300-amp panel, 3 days, $3,450). The plumber ran new 3/4-inch lines from the basement to each unit (2 days, $2,400). We installed all 6 Tempra 29 Plus units in a single day. I was on site for the startup on Unit #3.

I turned the water on. Click. The unit’s display showed the temp: incoming was 48°F (9°C). I set the output to 120°F (49°C). The unit drew 26.8 kW—right at spec. Water came out hot in 4 seconds. No fluctuation.

That moment—when the data matches the promise—is why I enjoy this part of my job. I’m no technician, but I know what a properly sized system looks like. And this was it.

One more detail: The Tempra 29 Plus has a digital display that shows power consumption in kW. It’s not just a feature—it’s a diagnostic tool. If you see it pulling less than 25 kW during a cold water event, you know something’s off (flow, voltage, or air in the lines). That saved us once on Unit #5—a tiny air bubble was reducing flow. We flushed it, and the unit hit 27 kW again.

The ROI: What the Numbers Say 6 Months Later

Data as of January 2025. I pulled the utility bills for the Grove Street building. Compared to the same period last year (with the old system):

• Electric usage: Up 35% (expected, since we’re off gas entirely)
• Gas usage: Down 100% (boiler gone)
• Net operating cost (electric + gas vs. old system): Down 18%
• Tenant complaints about hot water: Zero. Literally zero. Last year in the same period: 12.

The math works. But I have to be transparent: my experience is based on 6 units in a single building. If you’re working with a high-rise or a historic building with weird plumbing, your experience might differ significantly. I’ve only worked with mid-sized (6–30 unit) conversions. I can’t speak to how this applies to large-scale projects.

Final Takeaways (and a Bit of Honesty)

What I’d tell a colleague:

• Don’t skip the electrical load calc. The 27 kW rating is real—and it’s heavy. A 200-amp main panel might not handle 2 of these units in one building without a load shedder.
• Check pipe sizing with the Stiebel Eltron specs. A 1/2-inch line will choke a Tempra 29 Plus. Trust me on this one.
• Don’t assume a “package deal” saves money. The Comfort Solution bundle would’ve cost us $300 more per unit for a less reliable unit. That’s $1,800 over 6 units.
• Small orders matter. When I was placing this order—6 units, $8,700 in equipment—some vendors treated it like a nuisance order. Stiebel Eltron’s distributor didn’t. They sent product sheets, answered my questions at 4 PM on a Friday, and the units arrived on time. That matters.

Part of me wants to consolidate to one equipment brand for simplicity. Another part knows that redundancy saved us during that 2021 supply chain crisis. But for now, Stiebel Eltron is on my “shortlist without hesitation” list for electric tankless. I really should write down that list. (Note to self: do that.)

And yes, I’m also looking at an ecobee thermostat for the common area heating—but that’s a story for another day.