Viessmann Indirect Water Heater vs Tankless: A Procurement Manager’s Cost Breakdown (With Temperature Settings Guide)

There’s No One-Size-Fits-All Hot Water Solution

I manage procurement for a mid-sized facility company—about 80 people across three buildings. Over the past six years, I’ve tracked every invoice in our system: $180,000 in cumulative spending on heating equipment, and that’s just the hot water side. The conventional wisdom says “go tankless if you want to save money”. But after crunching the numbers on Viessmann indirect water heaters vs. tankless units (and a few weird items like patio heaters and Can Am X3 air filters), I’ve learned that the real answer depends entirely on your situation.

In this guide, I’ll break down three common scenarios and show you exactly when a Viessmann indirect tank makes sense, when tankless is actually cheaper, and—most importantly—how to set the temperature on a Viessmann boiler so you don’t waste energy (or risk Legionella). Let’s start with the scenario split.

Scenario A: You Already Have a Viessmann Boiler (or Plan to Install One)

If you’ve already got a condensing boiler like the Vitodens 200-W, the most cost-effective way to produce domestic hot water is with a Viessmann indirect water heater. Why? Because the boiler is already running at high efficiency (up to 98% on the gas side), and adding an indirect tank uses that same heat source without another burner or electric element. My TCO analysis across six years and three different facilities showed a 17% savings compared to standalone tankless units—once you factor in installation labor, maintenance, and lifespan.

Here’s something vendors won’t tell you: tankless water heaters require annual descaling and a $200–400 service fee every two years (especially in hard water areas). Indirect tanks? No burner, no scaling on the heat exchanger. The only regular task is flushing the tank once per year (which I do myself after learning the hard way—rookie mistake: I skipped the flush on a $1,200 tank and got a 2-year failure instead of 10+).

How to Set the Temperature on a Viessmann Boiler for Indirect Water Heating

This is where most installers get it wrong. The default boiler flow temperature is often set at 75–80°C (165–175°F), but with a Viessmann indirect tank, you can drop that to 60°C (140°F) for the boiler and still get 50–55°C water at the tap. Why drop it? Every 10°C reduction saves about 5–8% on gas consumption. Of course, you must avoid Legionella risk—so I set the tank to 60°C (the minimum recommended by WHO) and schedule a once-weekly thermal disinfection cycle to 70°C (which Viessmann controllers handle automatically). To actually change the setting: press the menu button on your Vitotronic control until you see “DHW temperature,” then use the +/- keys. (This was back in 2023, but the 2024 firmware is pretty similar.)

One more tip: if you’re using a Viessmann indirect water heater, dial the boiler’s “DHW priority” setting to “on.” That forces the boiler to heat the tank before going back to space heating—prevents cold showers (trust me, I learned that lesson when we forgot to configure it on a new install—cost us a client complaint and a 2-hour service call).

Scenario B: You Have No Boiler and Only Need Hot Water

If your facility doesn’t have a central heating system (say, a small office with electric resistance heat), then a tankless water heater might look attractive. And to be fair, the upfront cost is lower: a good tankless runs $800–1,200 vs. a Viessmann indirect tank + boiler combo at $3,500+. But here’s the experience override: everything I’d read said tankless is more efficient because there’s no standby loss. In practice, for our intermittent usage pattern (8 hours/day, 5 days/week), the standby loss on an indirect tank is negligible—maybe $15/year—while the tankless unit’s burner cycling on every draw actually lowered its efficiency. Plus, tankless units require a bigger gas line and venting upgrade in older buildings, which added $450–700 to our installation cost.

My recommendation: if you must go tankless, choose a model with a 0.9 UEF rating or higher, and budget for a whole-house sediment filter to extend life. But if you have any future plans for radiant heating or a boiler, skip the tankless entirely—the Viessmann indirect system will pay back within 5 years.

Scenario C: Outdoor Patio Heaters (and Why I Almost Made a $1,200 Mistake)

Different product, same cost principles. We needed patio heaters for an outdoor seating area. The cheap option was $200 propane units; the premium (electric infrared) was $600 each. I almost went with the $200 ones until I calculated TCO: propane refill costs $40 every 20 hours of use, while infrared uses $10 of electricity over the same runtime. Over a typical 6-month season (say, 300 hours of operation), the propane unit actually costs $600 more in fuel—more than double the purchase price! That’s a classic causation reversal: people think the $200 heater is cheap, but the usage cost dominates. We ended up buying four electric infrared heaters (surprise, surprise—from a brand that rhymes with “Schwester”) and saved $2,400 over three years. The key takeaway: always do a TCO spreadsheet, even for “small” purchases.

Scenario D: Non-HVAC Items (Yes, Even Can Am X3 Air Filters)

Wait—what does a Can Am X3 air filter have to do with heating? It doesn’t. But as a procurement manager, I buy all kinds of stuff: HVAC parts, vehicle filters, janitorial supplies. The prevention over cure mindset applies everywhere. I once ordered a batch of OEM air filters for our fleet of UTVs. The generic aftermarket ones were $8 each vs. $22 for the OEM. I went generic (rookie mistake: assumed “standard” means the same). After 50 hours the generic filter collapsed and let dirt into the engine—$1,200 repair. That mistake taught me to check specs (micron rating, pleat count) and not just price. For your Viessmann indirect water heater or boiler, the same logic applies: using an off-brand temperature sensor or pump might save $30 now but cost $500 in efficiency loss later.

How to Know Which Scenario Applies to You

Grab a piece of paper and answer three questions:

1. Do you already have or plan to have a boiler (for space heating)? If yes → Scenario A (Viessmann indirect tank). If no → go to question 2.
2. Is your hot water demand relatively low (less than 10 showers/hour at peak)? Then a tankless might work—but also consider a small electric storage tank if gas upgrade costs are high.
3. Are you buying something completely unrelated (patio heater, air filter)? Run the TCO calculation before purchasing. I built a simple calculator after getting burned twice on hidden costs—happy to share the template if you email me.

The point is: don’t let the lowest quote fool you. Five minutes of upfront analysis beats five days of rework. That 12-point checklist I created after my third mistake has saved us an estimated $8,000 in potential rework. And for Viessmann specifically, the indirect water heater + proper boiler temperature setting is the most efficient combo I’ve found—granted, it requires a bit more planning, but the payoff is real.