The U.S. sauna boom is real, and for good reason. Saunas are bringing better wellness, enhanced recovery, and a deeper connection to nature.
But here’s the truth: Not all saunas are created equal.
As the largest supplier of thermally modified sauna lumber in the United States, we see projects across every climate and application. With this unique opportunity, we are noticing a few costly mistakes. Here are the most common sauna mistakes to avoid when purchasing or building your first sauna—and how to get it right the first time.
1. Treating a Sauna Like a Shed (Not a System)
One of the biggest misconceptions?
Thinking a sauna is just a small structure you drop in your backyard.
In reality, a sauna is a performance system:
- Heat source
- Airflow + ventilation
- Insulation
- Materials working together
When one piece is off, the entire experience suffers—uneven heat, poor efficiency, or worse, long-term damage.
2. Choosing the Wrong Materials
This is where most first-time buyers unknowingly cut corners.
Standard wood may look good at install—but saunas are extreme environments:
- High heat
- Constant moisture cycling
- Expansion + contraction
That’s a recipe for:
- Warping
- Cracking
- Rot over time
Thermally modified wood changes the game here. The process reduces moisture absorption by up to 50–60%, dramatically improving stability and durability in sauna conditions.
The mistake: choosing materials for appearance alone.
The fix: choose materials engineered for heat, humidity, and longevity.
3. Undersizing (or Oversizing) the Heater
Your heater isn’t just a feature—it defines the experience.
Too small:
- Struggles to reach temperature
- Weak, inconsistent heat
Too large:
- Harsh, uncomfortable environment
- Inefficient energy use
Proper sizing depends on:
- Room volume
- Insulation
- Glass surface area
- Ventilation
Even sauna experts emphasize that heat quality depends heavily on correct sizing and thermal mass (stone capacity). In Finnish tradition, true sauna experience is defined by löyly—the convective heat and steam released when water vaporizes off high-mass, properly heated stones, creating a more stable and evenly distributed thermal environment.
The takeaway: A great sauna isn’t about hotter, it’s about balanced heat.
4. Ignoring Ventilation (and Airflow)
Bad airflow = bad sauna experience. It’s that simple.
Without proper ventilation:
- Heat becomes stagnant
- Oxygen levels drop
- The experience feels heavy and uncomfortable
Worse, poor ventilation can lead to long-term moisture issues inside the structure.
The mistake: treating ventilation as optional.
The fix: design airflow intentionally from the start.
5. Poor Location & Site Planning
Where you place your sauna matters more than most people think.
Common issues include:
- Poor drainage
- Inadequate electrical access
- Tight or unusable layouts
Improper placement can lead to moisture damage, inefficient performance, and costly retrofits later.
Just as important is what your sauna sits on. A proper foundation should be level, stable, and designed to manage moisture. Depending on your setup, that could mean a gravel base, concrete pad, pavers, or even a well-built wood deck. If using a deck, ensure it’s structurally sound, properly supported, and designed for outdoor exposure with adequate airflow and drainage beneath.
Pro tip: Think beyond install day—consider how the sauna will function year-round.
6. Designing for Looks Instead of Experience
Yes, aesthetics matter. But in a sauna, experience comes first.
We’ve seen:
- Benches that are too low
- Layouts that trap heat unevenly
- Designs that look beautiful—but feel uncomfortable
The best saunas follow a simple rule: Form follows function. When the design supports proper heat flow and comfort, the beauty naturally follows.
7. Thinking Short-Term Instead of 20+ Years
This might be the biggest mistake of all.
A sauna isn’t a seasonal purchase—it’s a long-term investment in your home and your wellbeing.
Cutting corners upfront often leads to:
- Repairs
- Replacements
- Frustration
The Thermory difference:
We’ve spent over 25+ years refining thermal modification technology—and we’re one of the only companies that has seen our products outlast their warranties in real-world conditions.
We engineer our materials to work with the sauna system—offering dimensional stability and moisture resistance so your sauna can perform consistently over time, not just on day one. Up front, it may feel that you’re spending a little more than you would on standard (untreated) wood, but the long-lasting value you’re creating is priceless.
Build it once, build it right. Start with materials engineered for real-world performance.
Photo Credits: Inland Luxury Sauna. Superior Sauna. Sauna House, Asheville, NC.
