Ed Note: This is part 1 of a 2 part post looking at electric sauna heaters. This post looks at brands, sizing, controls, and design. Part 2 will follow soon and address construction, spacing, repair, and gray-market sauna stoves.
I wrote a few months back about the outdoor sauna we were building in Southern California. Due to the brush fire hazard, local zoning, and nearby neighbors, a wood-burning stove really wouldn’t work for us. That meant going with an electric heater though I really didn’t know much about them at first. After doing months of research I’ve gotten quite an education and Glenn asked us to pass along what we’ve learned. Hopefully, Sauna Times readers find this helpful.
Electric Heater Variety
The variety of electric sauna heaters available in North America seems a bit overwhelming on first glance. There are at least ten different brands, each with several model lines. The manufacturer and retailer’s websites aren’t very helpful as they are dominated by marketing hype and claims of superiority without much substance. Most seem better at confusing rather than informing.
I started compiling a spreadsheet to sort them out and quickly noticed a surprising amount of commonality. It turns out that most of the available family sauna units are different variations of the same basic wall-mounted design. This was surprising until I understood two things:
- The US market is dominated by two big European manufacturers, Tylo-Helo and Harvia, and a couple of minor players. Much of the apparent variety comes from rebadging the same core design under different brand names.
- Only the most common designs that are likely to sell well are certified for the North American market. Most of the minor European manufactures haven’t been certified in the US. In addition, the major manufacturers have only certified their most popular variants. This has resulted in a rather bland selection compared to that available in Europe.
So remember that Finlandia and Harvia are the same. Amerec, Finnleo, Helo, and Polar all fall under the Tylo-Helo umbrella and are at best very similar using the same parts, with some models being rebadged units. Tylo, while being part of the Tylo-Helo umbrella, is a bit of an outlier as its models are unique. Of the North American manufacturers, Saunacore and Sauna Craft are the same and made in Canada. Scandia is a reputable US manufacturer, though its units look a bit too utilitarian for my tastes.
There are some Chinese and other off-brand units available that on the surface look to be bargains. I didn’t spend much time researching these and never seriously considered them. Sauna heaters by design generate high heat levels in a highly combustible environment. On top of that, they run relatively high voltage (240 Volts) through a metal box into which we dump water. They can outgas if not made of heat stable materials. Based on this, I only considered manufacturers with a long history of not burning down saunas, electrocuting or poisoning their customers. I’m not saying these off-brands are a risk, but I wanted to see some history before entrusting my family’s safety. Sort of like how no one wants to be a new surgeon’s first operation.
After browsing though some European sauna store websites, one can’t help but become envious at the huge selection available to the European consumer. It is possible to buy from these sites and have the units shipped to the US. There are some real challenges and potential pitfalls in doing this, that we’ll discuss in part 2 regarding “gray-market” heaters.
Sauna Heater Sizing
First thing to do is estimate the required heater size as it will drive all remaining decisions. These guidelines are from Harvia, but they’re sound and typical for the industry. Undersizing will cause real misery as the sauna will take an inordinate period to heat up if it ever gets there. Oversizing can be an issue also (though less of one IMO) as you don’t want the heater to feel like a blast furnace when it cycles on.
Note that these guidelines assume a properly constructed and well-insulated sauna. These also assume a 7 foot maximum ceiling height as higher heights significantly increase heating requirements. If you go that route you are on your own. Round the final answer up rather than down to prevent undersizing.
Guideline 1: Allot 1 kW of heater power per 45 cubic feet of sauna interior volume
Guideline 2: For each non-insulated square meter (10.75 square feet) of wall surface, add 1.2 cubic meters (42 cubic feet) to the volume of the sauna. This would include walls made of rock or brick, and large windows.
Guideline 3: For outdoor saunas in very cold climates, consider bumping it up a size if your calculated value is close to the standard size
- 5’ x 7’ family sauna with a 7 foot ceiling ->5 x 7 x 7 = 245 cu ft (guideline 1)
- 32” x 16” window -> (32 x 16)/144 = 3.55 sq ft / 10.75 = 0.33 sq meter. Thus 0.33 x 42 = additional 14 cu ft (guideline 2)
- Total = 245 cu ft + 14 cu ft = 259 cubic feet -> 259/45 = 5.75 kW
- Outdoors in a moderate climate -> no adjustment (guideline 3)
Thus we end up with a 5.75 kW need, bumped up to 6 kW or 6.8 kW as these are standard sizes depending upon the manufacturer.
A typical family sauna usually will usually end up somewhere in the 5 to 8 kilowatt (kW) heater range.
Electrical Power Needs
Anything above 2 kW (suitable for only small 1-2 person saunas) will require a dedicated 240 Volt circuit wired directly from the electrical service panel. This might seem overly complicated but it really isn’t as all modern US homes have 240 Volts available even if it only has 120 Volt outlets and appliances.
(Standard disclaimer: These points are passed along to educate. If you don’t know what you are doing or aren’t willing to spend some serious time doing research first, hire a qualified electrician to do the actual work. The National Electric Code has specific requirements on wire size, wire type, conduit size, conduit depth, grounding, breaker sizing, and other odds and ends that must be followed to ensure a safe and compliant installation. Some of these requirements aren’t intuitive and your family’s safety is at stake. )
A quick assessment of the home’s electrical panel will let you know what sort of shape you are in. Look for three things:
- The existing electrical service size in Amps – This can be found on the main breaker, usually labeled “MAIN” or “SERVICE DISCONNECT”.This will be a double breaker that is often larger in size than the others with typical values of 100, 125, 150, 200 Amps, or even higher.
- The existence of other 240 Volt appliances – These will be double breakers that serve large appliances such as electric ranges or water heaters, or an air conditioning compressor.Look for anything marked 30 Amps or larger.
- Spare spaces in the panel – Either spaces where the breakaway metal tabs have not been punched out or is filled with a plastic blank.
A family sauna heater will typically need a new 30 or 40 Amp breaker/sizing depending on the kW rating. Generally, expect a 6 kW to need a new 30 Amp breaker, and 8 kW unit to need 40 Amps. The exact current draw can be calculated by:
Heater size in Watts / 240 Volts = Current draw in Amps.
One kilowatt (kW) = 1000 Watts. Thus a 6 kW unit will draw 25 Amps, with wiring and breaker sized for 30 Amps, the next higher standard size.
If your existing service size is 150 Amps or higher you should be fine. If it’s smaller and you don’t have exiting 240 Volt appliances, you again should be fine. If it’s small and you do have existing 240 Volt circuits you will need to do a little more research.
As an example, an older home with a 100 Amp service with air conditioning, an electric water heater, and a new sauna heater all running at the same time could exceed the 100 Amp service. This isn’t dangerous as the breaker will trip and protect the home (assuming it’s in good working order). It will be extremely annoying though, particularly when one is trying to unwind in the sauna after a long day.
If you fall into this camp, a qualified electrician should perform a load assessment before going further. It is not as simple as adding up the breaker totals as no one uses all branch circuits to capacity at the same time. It’s a statistical analysis that determines the highest load the service will likely encounter in daily usage. If the load calculation exceeds your existing service level, it might be worthwhile to upgrade your service panel and feeder lines. Be prepared to spend several thousand dollars.
Assuming we’ve cleared that hurdle, next check to ensure you have two adjacent spare spaces in the panel. They must be adjacent as a double breaker is required with the trip levers tied together. If you have two but they aren’t adjacent, a competent individual can rearrange them in the panel to free up two next to each other. If you don’t have two, spaces can be opened up by using tandem (half size) breakers. Convert some of the existing 120 Volt circuits to tandems so you can use a full size double breaker for the new 240 Volt sauna circuit. Note that not all panels allow the installation of tandem breakers so don’t just assume this is feasible without checking first.
If you’ve made it this far, it’s time to start drilling down into the available heaters.
Built in Controls versus Remotes
The next major decision point is the heater controls. The lowest cost models simply incorporate the controls into the heater itself, usually two knobs located at the bottom of the unit. There’s a temperature knob and a time knob, all one really needs to enjoy a good sauna. Simple, straight-forward, functional, and relatively inexpensive.
Personally, I was looking for something a bit more sophisticated and I also wanted the controls outside the sauna itself since I have small kids and didn’t want them monkeying with them. There are manual remote controls that do little more than move these knobs outside the sauna, perhaps with a coarse time delay knob added on for some additional convenience. These will add one or two hundred dollars in cost and I’m not quite sure I get it. To me these look like they belong in a gym or a hotel fitness room and they also make an annoying ticking sound. To each their own.
The next step up is a full digital control that allows programming the specific temperature, sauna time, and delayed start. It also incorporates sauna lighting and an optional exhaust fan control. Further, the control can be programmed to automatically start and end a drying cycle and activate the exhaust fan and the end of the sauna session. There are also a few other customizable settings in the controls. It includes a digital temperature readout much like a home thermostat.
These controls are typically an add-on and the prices can cause sticker shock being upwards of $500. While they aren’t cheap, they aren’t quite the overpriced rip-off they might seem to be on first glance. Remember that the cost of the heater itself will be cheaper without the built-in controls, usually on the order of $100 or more. Also, most of these digital controls will typically move all the electronics except the heater elements and temperature sensors outside the hot room into a separate, remote contactor box. This separate box is usually included in the remote control package price.
There is a real benefit in wear and tear in locating these parts in a room temperature environment. The remote box will typically include a circuit board with some sort of microcontroller and one or more heavy duty contactors (electrical relays). Electronics don’t like either heat or humidity, and are subject to early failure unless specifically designed and tested for such environments (i.e. military grade). In addition, these types of failures are often intermittent thus being difficult to troubleshoot. As the electronics are usually the most expensive components to replace, putting them outside the hot room makes good sense to prolong life.
The next step up the line uses a wi-fi connection to allow turning the unit on/off from a distance further then feasible using a wired remote. The Tylo Sense Elite line incorporates this feature but be prepared to spend big bucks. Tylo states unequivocally that this feature is for turning on the unit from another location on your property. It specifically is not intended to turn on the unit from a location away from home. So don’t expect to turn it on from the office to have it ready when you get home.
Shop around as the control package price for the same unit can vary wildly among different distributors. (When comparing prices do make sure the controller model numbers are exactly the same as there are a variants that look the same but intended for different heater units.) Provided the controller is compatible with the heater, there is no reason you need to buy them from the same distributor if you find deals on each. If shopping online (E-bay in particular), do ensure that the controller is certified for the US market. European versions are configured to operate on different voltage forms and will not work on standard US 240 Volt single-phase power without significant modification.
Rock Cavity Design, Size, and Distribution
Rocks are essential for any sauna heater as they act as a heat sink, and thus allow soft steady heat over time. An analogy from other applications might be a reservoir at a hydro-electric power plant or a flywheel in an engine. Its purpose is to store energy and smooth out delivery. A sauna heater without rocks would provide a blazingly hot blast when the heating elements cycled on and then the sauna would quickly cool when they cycled off. Ideally, there is should no noticeable temperature fluctuation during heater element cycling.
So just as a large reservoir provides more steady and reliable hydro-electric power than small reservoir, does that mean the more rocks the better? To an extent, yes. There’s a point of diminishing return where more rocks makes no noticeable improvement in sauna temperature variations. More importantly, more rocks can significantly increase sauna warm-up time as the rocks heat up much slower than the surrounding air. A major selling point of an electric heater is their convenience. If it takes two hours to warm up the sauna then one may as well build a fire.
Of course the rocks are also the source of steam when water is thrown on them, aka loyly. More rocks are better here too as the heater can instantly convert more water to steam with less running through and ending up as a puddle on the floor. However if there are too many rocks for the heater size then the rocks might not get hot enough to make steam in the first place.
You probably get the picture that the rock configuration requires some compromises to balance these competing factors. Different compromises result in different heater performance. Unfortunately, 80 to 90% of the heaters certified for the US family sauna market use the same basic setup with the same compromises (unlike the European market). The standard is a wall-mounted unit, a fairly deep rock cavity, 45 lbs of rocks, and the rocks in direct contact with all heating elements. Most electric heater models are the sauna equivalent of the Toyota Camry, functional and pragmatic, they get the job done but aren’t very inspiring. Not only that, most are pretty drab in appearance, a real shame after all that work in building the sauna and hand selecting cedar boards.
Some Imaginative Designs Available in North America
There are some notable exceptions that show some imaginative engineering. Tylo heaters use side chambers where a large portion of the heating element only contacts air. Rocks are limited to the center cavity and are fewer in quantity than that of competing models. Some hold as little as 20 lbs of rocks. This results in fast sauna warm-up times.
You would think this approach would cause sharp heat and large temperature fluctuations but Tylo implemented a clever solution. Virtually all family sauna heaters use three heating elements that turn on and off together. Tylo, on the other hand, operates their heating elements in stages. Rather than turning on or off all three elements at once, it changes the number of active heating elements based on the desired temperature change. This helps smooth out temperatures over time despite the small rock quantity.
There are also some family sauna free-standing towers that have been recently certified for North America including the Harvia Cilindro and the Finnleo Himalaya. These have huge rock capacity as they hold over 200 lbs. of stones. There is also plenty of exposed rock surface for throwing water thus creating strong bursts of loyly. These recent entries into the US market hopefully indicate we’ll soon see more true variety available to the US consumer.
We ended up selecting the Harvia Virta, another imaginative model recently certified for North America. The Virta is a floor standing unit that holds 110 pounds of rocks. It uses a clever cage to separate the rocks from the heating elements that Harvia claims will speed up warming time. We selected it based on its features and lots of good feedback and comments on European websites (thank you Google translate!) and we’ll post a report once we are up and running. Plus the unit is just stunningly beautiful to look at, using high quality polished stainless steel punctuated by crisp, straight lines.
When our unit arrived it was plastered with hideous orange and white warning stickers that assume the user is an imbecile. Not only that, they stop just short of telling you not to turn the unit on at all if you know what’s good for you. Somehow I doubt the units shipped within Finland end up like this. Fortunately they are removable and will be coming off ASAP.
This article ended up a bit longer than originally intended but I’ve become a bit obsessed with these units over the last year or so. Our sauna is on track to be up and running in about 6 weeks (middle of Summer unfortunately) after we finally got started in March. It’s been quite an adventure that did include some electrical service upgrades. Despite all that, it’s been a blast and Glenn’s e-book and email assistance have been a huge help.
Believe it or not, there’s a bunch more to cover on these units that I’ll put in a follow-up post.
Ed Note: For even more chatter with Jeff, I couldn’t resist copy/pasting our email conversations about electric sauna stoves, here. He is miles beyond me in knowledge and fresh information on the topic, and i’m most pleased to share this with you.