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The definitive word on what kind of glass to use for windows in the sauna (I can really see clearly now)

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I have built a bunch of saunas. I help hundreds build their own sauna thanks to the book I wrote, and an unwavering enthusiasm to help folks build their own kick ass saunas (with no compromises).  The question of what kind of glass to use in a sauna comes up frequently.

So, what kind of glass should I use for windows in the sauna?

Well, I finally got through with an expert in the field.  And it took a lot of work.

Folks in the glass industry seem about as temperamental as the product they sell. Industry experts that I have spoken with are generally not the most patient and don’t seem like a lot of questions from DIY’ers. Most are more accustomed to dealing with tradesmen.  I understand how patience can wear thin as ordering the right custom cut glass can be an involved process.  There are many glass options to choose from, and every order involves a careful verification of dimensions.  Mistakes are costly.

However, I have finally been connected to an expert in the field who was patient and friendly, and locked into my barrage of questions.  Michelle is a glass industry expert with 17 years experience.  Even better is that she told me “I never stop learning” which tells me that she is open minded enough to keep expanding her knowledge in the field.  (This, by the way, is exactly my theory of sauna building, which is why my ebook is open to involving with sauna builders’ generated content).

Ok, enough of all that, here’s the scoop:

For windows in your sauna:

  1. Plan your sauna window carefully.  I am a big fan of transom windows up high. – 16″x 30″ or so.  They don’t get in the way with whatever is underneath, and allow privacy.  There is the candle window, and window in the hot room door.
  2. Contact a local glass company.
  3. Order 1/4″ insulated tempered glass, cut 1/8″ to 1/4″ less than your rough opening.
  4. Frame in the glass using the same material as your hot room (cedar paneling ripped to size).
  5. Run a bead of silicone around the inside and outside of window.

Insulated tempered glass is two pieces of glass bonded together.  This creates an insulated unit.  This system reduces moisture on the glass.  This system helps facilitate the temperature extremes of a sauna hot room and a cold winter’s night.

What if the seal of the double pane glass breaks down and moisture gets between the glass?

This shouldn’t happen, but if it does, we are shit out of luck.  We either have to live with it or replace the glass.

What about cost?

a 16″x30″ insulated tempered 1/4″ piece of glass costs $93.00.  That’s about twice the price of single pane.  But this price is a fraction of the price of buying a window.  We build our saunas one time.  Let’s use the best glass option we can find for our sauna windows.

a hot room transom window as viewed from the outside, with saunatimes promotional material underneath.

For more discussion and clarity on windows in the sauna, please read here.

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10 thoughts on “The definitive word on what kind of glass to use for windows in the sauna (I can really see clearly now)”

  1. Hi Glenn! Curious on your thoughts about heat loss through a large hot room window? Also, is this same 1/4″ insulated tempered glass suitable for a mobile sauna bouncing down the highway?
    Looking forward to your thoughts, thanks for you commitment to sauna.

  2. Is this bead of silicone special heat silicone. It seems like regular silicone would melt inside the hot room?

    I am thinking of using my old triple paned tempered patio door glass that lost it’s seal on the third pane. I will cut off the third pane of glass and still be left with a double sealed tempered glass unit.
    Does this seem ok?
    The glue that seals them won’t melt?

    Tom from Manitoba, your northern neighbor. 🍁

  3. Hi Tom:

    shhhh.. don’t tell anyone but I’ve used regular silicone to glaze around my hot room windows. And they’ve held up. That said, if special heat silicone is available, I say, sure, get that and use that!

    Greetings neighbor.. i’m looking to get up your way. Therma action!

  4. Hi Glenn, is there a reason why you recommend framing a window yourself (rather than buying a manufactured window) in your book?
    FYI: Our window will be in the hot room, we’re don’t have a changing room. The glass will be tempered and insulated.

    Tom, were you able to source special heat silicone? Thanks both!

  5. Hi Wayne:

    Windows are factory made with vinyl or aluminum or pine framing. None of these materials are good for sauna. We’ve got heat differentials and a shit ton of moisture that can sit and pool around the trim and jam area. So, it’s nice to get fixed glass and use a material like cedar or heat treated product to frame around.

    Also, fixed glass is usually a better choice than operative windows. Using windows for ventilation sounds good but it leads to all kinds of hassle potential: in cold climates, the heavy steam trying to escape hits the cold and icicles, jamming the sliding mechanisms. And in wet climate, well all that moisture can short live the sliding mechanisms of operative glass windows.

    There are plenty of examples where people frame in windows for hot room sauna action. Especially these old school windows reclaimed from cottage remodels. it’s cool to not be rigid on all this stuff, but above is a guideline that may help you along.

  6. I have an existing insulated double-pane glass casement window in the space I’m converting into a sauna. My guess is a should replace that with a tempered piece of glass? My question is how bad would it be if I didn’t? Would insulated glass shatter at 200 degrees?

  7. You could be just fine with this casement window. The issue with windows is a couple things. The main one is that they are cased in either pine, vinyl, or aluminum. None of them are good in intense moisture thermal extreme climates. That’s why our best gig is a fixed piece of glass and frame around it with cedar – moisture happier species.

    And fixed glass Vs operative windows:
    We want steam to move out of the vents Vs through cracks in windows. But there are plenty of awesome saunas with operable windows. All great.

  8. Hi Glenn in your ebook you said to use 1/2 ” glass but the forum it says 1/4″ glass, what is your preference ?

  9. 1/4″. That’s a type’o in my book. and above article discusses the thermally insulated vs. single pane version.

    General rule:
    smaller window: single pane 1/4″ is more than fine. Even 3/8″ or 1/4″ works.
    larger window: A glass company can spec out a double pane thermally insulated. This is the trend these days… big glass.

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