Why Water Kills Heaters (When You Do It Wrong)
Electric sauna heaters have heating elements – usually stainless steel coils or tubes – sitting beneath or between the rocks. These elements run extremely hot. When cold water hits them directly, you get rapid thermal shock: the metal expands and contracts suddenly, and over time, this causes cracking, warping, and failure.
The rocks are the heroes here. They’re designed to absorb and store heat and handle thermal shock far better than metal ever could. Pour water correctly – onto the rocks, not the elements – and the stones flash that water into steam. In contrast, the elements stay dry and happy.
The problem? Most heaters don’t come with clear instructions on this. People assume you just throw water in the general direction of the hot stuff and hope for the best. It works for a while. Until it doesn’t.
The Right Way to Do It
Here’s how to not become the guy who calls me in a panic:
Use a ladle, not a water bottle.
I cannot stress this enough after that phone call.
The traditional Finnish ladle exists for a reason. It gives you control – how much water, exactly where it lands. A water bottle? You’re squeezing and hoping. A bucket? You’re flooding everything. A coffee mug? I’ve seen it. Please don’t.
All of our custom-built saunas, traditional and modern, come with a wooden bucket and ladle as standard. Not because we’re being generous – because we’ve learned what happens when people improvise.
Aim for the top rocks only.
The rocks on top of the pile are the hottest and the furthest from the heating elements. That’s your target. Let the water hit the top layer, flash into steam, and dissipate upward. Never try to get water down into the rock pile where the elements live.
Small pours. Patience.
About 100-200ml per pour is plenty. You want enough for a satisfying burst of steam, not so much that water pools and drips down through the gaps.
Multiple small pours beat one big splash. Wait 30 seconds to a minute between rounds to let the rocks cool down. Patrick calls this “letting the stones breathe” – and yes, he says it in a tone that suggests I should have known this intuitively. I did not.
Warm water, not cold.
This surprised me when I first learned it. Cold water creates sharper thermal shock – both on the rocks and on any elements it might accidentally reach. Warm water produces gentler steam, reducing stress on everything.
Some purists insist cold water makes better löyly. Maybe they’re right. But cold water also shortens the life of your heater and rocks, and I’ve never noticed a difference in the steam quality. I keep my bucket inside the sauna so the water’s already warm when I use it.
Wait for the sauna to actually heat up.
This one I learned the hard way. Early on, I was impatient. The thermometer hit 80°C, and I started throwing water immediately. Weak steam, puddles forming at the base of the heater, Patrick giving me the look he gives me when I’ve done something stupid.
The rocks need time to absorb heat throughout, not just on the surface. If you pour water on stones that are only hot on the outside, the water penetrates to cooler layers and doesn’t vaporise properly. You get disappointing steam and water dripping toward places water shouldn’t go.
Give your sauna at least 30-45 minutes before you touch the ladle. I don’t start until 40 minutes minimum now, and the löyly is infinitely better.
Signs You’ve Been Doing It Wrong
If you’ve owned your sauna for a while and haven’t been paying attention to technique, here are some warning signs:
Less steam than before. Same amount of water, weaker result? Your rocks might be degrading, or your elements are struggling.
Metallic or burning smell when you pour. This usually means water is reaching the elements directly. Not good.
Visible rust or white mineral deposits on the elements. Take a look periodically. If you see corrosion where water shouldn’t be reaching, you’ve got a technique problem.
Longer heat-up times. If your sauna’s taking longer to reach temperature, your elements might be losing efficiency from repeated thermal stress.
Rapidly cracking rocks. Some cracking over time is normal. Rapid degradation suggests too much water, water that’s too cold, or both.
A Word About Rocks
While we’re here, the type of rocks in your heater matters more than most people realise.
Proper sauna rocks are dense, non-porous volcanic rocks like peridotite, olivine, or vulcanite. They’re specifically chosen because they handle extreme heat and repeated thermal shock without cracking or, more importantly, exploding.
Do not – and I really mean this – use random rocks from your garden, the beach, or a riverbed. These can contain moisture pockets that turn to steam, causing the rock to explode. I’ve heard stories of rock shrapnel embedded in sauna walls. Those are the lucky outcomes. Don’t be the person who learns this lesson the hard way.
If your rocks are crumbling badly or no longer producing good steam, replace them. Most manufacturers recommend every one to two years with regular use.
Different Heaters, Different Rules
Everything above applies to traditional electric sauna heaters with exposed elements and rocks.
Wood-burning heaters are more forgiving – no electric elements to damage. You can be more generous with water, though you should still aim for the rocks rather than the metal parts. However, we don’t recommend using them in Thailand as finding wood is not so easy.
Infrared saunas don’t use rocks at all. There’s nothing to pour water on, and doing so would damage the infrared panels. If you want löyly, infrared isn’t your sauna.
Combi heaters (sauna + steam) often have built-in water systems that automatically produce steam. If you’ve got one of these, follow the manufacturer’s instructions for the water system rather than pouring manually.
What I Hope You Takeaway From My “Rant”
This bit of löyly know-how isn’t rocket science, but treat it with respect anyway. Ladle in hand, water only on the top rocks, small splashes of warm water, and patience while everything heats through. Get the basics right, and your heater stays healthy for the long haul.
Skip the technique and keep flooding those elements? You’ll be forking out for repairs that were never necessary.
That customer I mentioned at the start? He’s got a new heater now, a proper wooden ladle, and obvious instructions. Six months later, everything’s running perfectly. Sometimes the simplest fixes make the most significant difference.
If you’ve got questions about any of this – whether you bought from us or not – feel free to get in touch. I’ve made enough mistakes with saunas that I’m happy to help you avoid them.
