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Sizing an electric sauna heater? Here’s why 9kW is your max

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When building a sauna with an electric sauna heater, it is critical to choose the right sauna heater. Most everybody puts their focus on the hot room, but generally speaking, the main reason why 9kW is your maximum size electric sauna heater has nothing to do with your hot room.

Want to guess why 9kW is your max size for home saunas?

Here’s a clue:

Electric service panel, with room for an electric sauna heater

Yep, you got it. The control panel. Homes in North America are single phase electric. Power comes in from the power company right to the electrical box. We can draw off power for appliances like clothes washers, arc welders, and power amps for heavy metal guitarists in the form of a dual breaker 20 amp circuit. 20 amp +20 amp = 40 amps. That’s good! We start pushing beyond this, and well, appliances can start tripping (without Psilocybin).

a 40 amp double pole breaker – recommended for electric sauna heater applications, wired directly to the control panel

Now, when it comes to firing up our home saunas with electric sauna heaters (an oxymoron, I know) if we start trying to log jam a commercial electric sauna heater into our residential saunas, well, chances are you’ll be seeing colors and trails from your trips to the control panel to reset your circuit breaker.

Good news when it comes to electric sauna heater sizing

9kW is your max. And 9kW is a great size for most all residential applications. And 9kW is the max that sauna heater manufacturers UL certify. You can refer to sizing charts on sauna heater manufacturer websites. What you will find is that a 9kW fits a 6’x8′ or 7’x7′ or even an 8’x8′ hot room like a baseball glove (and not an OJ Simpson glove). To best understand sauna heater sizing, consider that a an electric sauna heated sauna performs best when the stove is “on” no more than 30% of the time. Like Goldilocks and porridge:

A sauna heater undersized for your hot room will:

  • be on too much.
  • suck the oxygen out of the room.
  • overheat the rocks and your ears.
  • give löyly that will make you want to rush out the hot room door.
  • be apt to provoke your guests to say “This sucks. I don’t like sauna.”
  • incur increased energy consumption: the heater runs more frequently.

A sauna heater oversized for your hot room will:

  • be on too little.
  • heat the room too fast.
  • underheat the rocks, and your body, and your soul.
  • give löyly that will make you feel like a wet diaper (wimpy and wet).
  • be apt to provoke your guests to say “This sucks. I don’t like sauna.”

Do you get the idea of how important this is? 9kW is the max for residential purposes. Let’s size our hot rooms and heaters appropriately.

A 6kW electric sauna heater well sized for the hot room (and the home service panel!).

Editor’s note: There’s always the potential for a bigger hammer. You’ll sometimes find commercial sized electric sauna heaters in residential homes, especially newly built mega homes with big ass basements that go on and on. In these instances, the electrician will need to install an 80 amp breaker to carry the load of a 15kW sauna heater, for example.

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21 thoughts on “Sizing an electric sauna heater? Here’s why 9kW is your max”

  1. I have a Dundalk 780 series barrel sauna. It is a 7′ diameter x 8′ long barrel. But also has a 4′ change room and a 2′ porch. See link below (page 37 and page 38 of the catalog – “Model 780 with change room and porch”).

    I sized my heater taking into account the option to heat my change room in case I have additional guests. By my estimation, my sauna is ~390 cubic feet with the change room volume and ~250 cubic feet if I only consider the 7′ diameter x 8′ long “sauna room”.

    I likely made the mistake of oversizing my sauna heater (12kW HUUM Hive). Wish I had read this article earlier!! The electrical is all complete (not easy) to support the 12kW HUUM Hive. But I am open to eating the cost of the overkill electrical and downsizing my heater if that will optimize the experience for my guests and I.

    It is an outdoor sauna and I have added some extra baffles to increase air flow through the sauna. It’s also an outdoor barrel in Canada (very cold winters) so I figure the barrel will lose more heat to surrounding than the typical HUUM heater calculators may assume.

    The HUUM calculator says the 12kW heater is appropriate for a sauna room 424 cubic feet (on the low end of the range – 424 cubic feet to 883 cubic feet is the published range by HUUM for the 12 kW Hive).

    Just curious your thoughts. You seem to know what more about a good sauna experience than I do. I ultimately just want a great experience.

    It’s just recently installed and has not yet been “fired” up so I cannot speak to performance using the 12 kW heater. My instinct is telling me to keep the 12 kW heater for now and if necessary (based on a poor sauna experience), downsize the heater later. Do you have any thoughts on this approach?

  2. My instinct is to go for the sweet spot / right size heater from the beginning. But there’s a good chance that if you install the 12kW and it doesn’t heat right, you’ll be able to sell it… so that’s good too.

  3. Thanks for posting my comment Glen. And the response. For my reference, is there a specific size HUUM heater you believe is more appropriate for my set up? Sweet spot / right size? Or do you think it is best to comply with the published heater size tables? I am surprised there are not different tables for outdoor versus indoor saunas. Mine is an outdoor barrel sauna. Is there a typical factor people use to correctly size outdoor versus indoor sauna?

    Anyways, thanks again for the response. I appreciate it may be difficult for you to offer any detailed recommendations on sizing for my particular sauna set up.


  4. Hi Komal:

    Thanks for understanding. Yes, as you say, it’s hard for me to offer specific recommendations. The bottom line on sizing, with electric, is that we want our heater to cycle on/off about 30% of the time. Like goldilocks and porridge: just right.

    You’re right.. heater size recommendations are very much dependent upon temperature outside the hot room. Heater size relative to hot room tables from heater manufacturers most likely assume indoor application, where we’re talking everything around 70°f. (21°c.). When I say everything, I mean, rocks, benches, walls, etc. That’s a huge difference from outdoor applications where in many places, the hot room climate is not only affected by big temperature differentials from the door opening and closing, but the “little engine that can’t” syndrome of an electric heater chugging along, fighting hard to heat up all the mass in the hot room.

  5. Hi Glenn,
    I was looking into the Iki kiuas for my 420 cubic ft. sauna. I live in California so this outdoor sauna/poolhouse will likely not be subject to temperatures below 28 degrees F. Will the 9kw kiuas work for this size sauna? I was looking also at the Harvia and Helo columnar kiuas.

  6. Hi Glenn,

    I’m in the process of finding the perfect size electric heater for an outdoor barrel sauna (I already have the barrel). The size of the barrel sauna is 8’x6’. There is a glass door and it’s obviously not insulated. The sauna will be used in -10c to +20c degrees so it would loose heat quicker I would imaging.

    Would a 9kw heater be overkill for this scenario? What would you recommend to for the perfect kw heater ?

    Thank you!

  7. Dave:

    Tough call. the issue with overpowering your hot room is that the stones provide wimpy löyly, as you know. I’ve not experienced your barrel set up, so I can’t give you a quality suggestion. If I had to roll the dice, i’d probably do the 6kW and if it became the little engine that can’t, sell it and trade up. But that’s just my take from my limited experience with electric barrels.

    Sauna on Dave!

  8. I have a Hurricane Industries heater I just purchased secondhand and I cannot figure out the KW. The sauna is a lovely classic- made by Leisure Bay-both out of business now. Any advice on how to research this further?

  9. Hello! I have an XXS outdoor wooden barrel sauna (1.10m x 1.9m or 3.6′ x 6.3′) and am not sure if I should go with a 4.5kw or 6kw heater. The sauna fits max 2 people, there is a glass door and it’s not insulated. The sauna will be used in -10c to +20c degrees. Will 6kw heater be too much or can I oversize it a bit? many thanks!

  10. This is a tough one. It’s like goldilocks and porridge. Too much kW and the room gets hot before the rocks. Too little kW and the elements glow red too long, fighting to keep up, like a little engine that can’t.

    I recently came back from an electric sauna research retreat. I took 16 electric saunas in 17 days. I got it down to this: fire up the electric sauna for a good hour plus, then shut it off and sauna, and make löyly. The steam is real when it doesn’t hit red hot elements. If you throw water and the elements are hot, the steam is “scorchy”, a buzz kill. This may not be your answer, but hope this helps you get closer to deciding.

  11. I need a bit of help if possible. I live in a cold climate with average temps of high of 28 F and average low temp of 5F in Dec, Jan and Feb. (this winter it was -25F on a number of mornings with highs in the single digits) and am looking to purchase an outdoor sauna. I was initially thinking about a barrel sauna, but and I’m concerned that a barrel sauna will not work in these cold temperatures. I then was informed of a insulated sauna that is 2.21 M wide x 2.19 m length x 2.46 m height with a window that’s 2.21 m wide x 2.46 m height, calculating out to an effective volume of 20 cubic meters. What size electric heather would you recommend? I will bring an electrician in to be sure I can provide enough power to the heater, probably with a sub panel.

  12. Hi Glenn:

    Sizing an electric for outdoor cold climate application is a tricky thing. The above article was written in context of indoor application, where everything – rocks, benches, walls – is starting from ambient. With cold climate action, the electric heater chugs along like a little engine that can’t, but over time, can. The other dynamic is changing room, and I encourage you reading this post which is a super critical consideration, not just for hot room microclimate optimization (HRMO – cough!) but for changing room microclimate optimization.. eg. being able to equalize body temp in a cool, chill climate free from cold winds whipping down the alley at dawn.

    Anyhow, notice how I wrote a ton without answering your question? Different electro heater manufacturers offer different answers. And holding them accountable to their recommendations is a good start. As is 9kW.

  13. I accidently pulled the trigger on the 8 kw and according to the specs in the manual I’m way oversized. My question; Iwill have a large window 57″ x 38″ and gets cold here in Wisconsin. The 6 seems to fall at the very top or a little over the max recommended. Will the window help get me more in loly land. Thank you. And I’m now reading the book I bought from you since I’m almost halfway finnished with the sauna!

  14. Hi Jack.. yes, sizing your heater is like Goldilocks and porridge. Not too big, and not too small. As you’re on the oversized situation, you’re probably experiencing your hot room getting quick fast, but the rocks kind of wimpy. Your window will help. If you get some air movement in there, your thermosensor will be tricked into thinking it’s cooler in your hot room, which is a good thing.

    I wish I could give you more precise direction on this situation. Maybe in winter you’ll develop more tricks for your 8kW. It is solvable!

  15. Hello,

    This article and comments have been helpful! We are planning to buy a HUUM Mini 6 for our hexagon shaped basement sauna that is approx 320 sq ft. The Mini 6 fits our electrical set up but seems to be on the small end for our square footage. However, being in the basement and fully insulated, there shouldn’t be much heat loss, so I think we are OK going with the 6 instead of the 9kw. Thoughts?

    My question is: HUUM offers two different rock size options, 1″-2″ and 2″-4″. Is there an option that is better for our situation? Do the larger rocks retain heat longer? Do the smaller rocks heat up more efficiently? Or is it just a matter of aesthetics?

    Thank you!!

  16. Hey Matt:

    You’re asking good questions. 6kW for indoor application with your situation is like a baseball glove that fits. I like rocks of different sizes, as they conduct, hold and release heat and steam variably.

    I’m going to email you. and glad you’re advancing.

  17. Hi Glenn, Jason in Ohio here.
    I’m building a sauna in my gurage that’s just under 500sq’. Will a 9kw work?

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