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:
- 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.
- Contact a local glass company.
- Order 1/4″ insulated tempered glass, cut 1/8″ to 1/4″ less than your rough opening.
- Frame in the glass using the same material as your hot room (cedar paneling ripped to size).
- 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.
For more discussion and clarity on windows in the sauna, please read here.
45 thoughts on “The definitive word on what kind of glass to use for windows in the sauna (I can really see clearly now)”
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.
As for large I’m going to suggest approximately a 3ft by 5ft window
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?
Thanks,
Tom from Manitoba, your northern neighbor. 🍁
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!
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!
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.
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?
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.
Hi Glenn in your ebook you said to use 1/2 ” glass but the forum it says 1/4″ glass, what is your preference ?
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.
Hey Glenn – I have a dual-pane tempered Marvin window with pine interior frame that I was planning on installing in the sauna room. Am I going to regret this decision? What things will I experience in going with that? Thank you!
We’ve had great results with this exact type of window and from the same window company. If you type “Jon Sabes” in search bar, you’ll see his sauna. Similar window ! Holding up very well. And thermal goodness.
If framing a piece of glass for a window (20″ x 50″) do I need to account for expansion and contraction to avoid having the glass crack? How do I do this and ensure this is sealed from the elements? I live in BC with massive amounts of moisture.
Look forward to your comments.
Kevin, in my book, I think I mention how it’s a good idea to put a little cork down at the base of the glass, before framing around the glass. Those little cork squares come from glass companies, and you usually get them when you order your glass, to keep the glass from rubbing together when stacked.
Other than that, we like to use clear silicone around the perimeter to keep the moisture out. This material does flex a bit.
Hello Glenn
Is it possible to use the tempered glass found on shower doors for a sauna ?
I am trying to cut costs on my sauna plans and used tempered glass shower doors come up regularly for sale on marketplace.
Ty
Paul
Yes! there’s nothing wrong with this concept and its resourcefulness. The one thing to be on guard for is proximity to the sauna stove. As we know, saunas getting north of, say, 200°f. is one thing, but heat off the stove can get that glass a lot hotter and subject to no bueno thermal shock and awe.
There are nice stained glass transom windows out there, seems flimsy to me though. What do you think of that? Should it be a special kind of stained glass? Lead is probably no good as well.
Yes to all you say, Bridgett.
Wonderful to find an existing stained glass window to use as a candle window but someone can check the glazing for lead.
And there are some beautiful stained glass manufacturers making great art. Would be nice to support their right brain action. Reminds me of Angler Fish Sauna. https://www.saunatimes.com/saunatimes-guest-posts/mobile-anglerfish-sauna-bends-the-rules-of-conventional-sauna-building/
Hello Glenn & Sauna Community!
My wife and I are converting an 8×10′ shed into a backyard sauna. The structure was built with a 2×3′ functional, vinyl-framed, insulated window that’s in (what will be) our hot room. We’ve been reading up on how tempered glass is best, but in the interest of keeping what we already have, do you have any tips on how to best protect this window? A friend suggested we build some sort of removable heat-shield for the window itself to reduce the radiant heat of the nearby stove. Is it worth it to swap the window out with wood-framed tempered while we’re in the build-out process, or do we make modifications to help work with what we got?
Thanks much!
Keegan
from Madison, WI
Keegan,
I have a vinyl framed interior window in my hot room at my cabin, we built in 1996. I didn’t know better back then. The window has shown some minor warping, but it still functions fine.
I suppose if you’re in the build out process, you could take the window out, but if it were me, i’d set the interior trim such that you could gently pry bar it out, and get after this window with a sawzall to replace after the fact. You may be fine, as mine has, over the decades and if not, you have a replacement plan. sauna on keegan!
I have a piece of 3/8 thick plexiglass- any reason I shouldn’t use that?
I’d avoid that material. Not reliable over the long haul with temperature extremes and hot and cold.. and then, not sure the service temp rating for plexiglass. My feeling is that even if it is high, we may not know about any potential offgassing. That’s my instinct, anyway!
Hi Glenn. I have an Almost Heaven Auburn Sauna kit that I installed in our garage in NY. The sauna has full length tempered glass windows and door on the front. During warmer months the sauna heats up and holds heat well. Now with temps dropping, It is taking double the time to heat up and looses heat fast once set temp is reached. I have a Huum Drop 6 heater that is recommended for the sauna size with amount of glass included in the calculations.
My question is… Is it OK to cover the glass with some sort of heat approved insulation to reduce heat loss thru the glass? If Yes, on the inside or out outside of the sauna glass window/door? and with what type of material?
Hi Shawn.
I hear you on your issue. I think you could try a $40 solution by purchasing a 4×8 sheet of rigid polyiso and cutting it to size for your window and taping it to the window, on the outside. It’s not a great solution. You’ll be looking at it while sitting on the bench. How’s your ventilation in there? Good air movement helps with the heat, believe it or not.. it’s like wind chill in reverse. You can read about this more here on this website, as you may know. Hope this helps!
Anyone wanting to know the thermal and acoustic value of a window configuration. May contact Element Material Technology in St Paul MN. We can consult regarding the best glass for your specific application.
Regards,
Bob Metzler8
robertmetzler@outlook.com
Fenestration Testing Technician.
Element Materials Technology
This is very helpful! I am contacting glass companies and getting a range of costs, and two companies told me it’s impossible to do an insulated double pane at 1/4″ thick– that no one can do this. So is it each pane is 1/4″, not the entire piece? Also I am hearing it for a window 38×18, a 1/2″ thick piece of tempered glass would hold heat just fine, not need for double pane. Considering the big price difference, I would go that route but only if that is in fact true. Is if important for double paned insulated, or is thicker piece of single pane glass okay? Thanks!!!
I like single pan tempered for a transom window like 38×18. it works great, and heat loss isn’t that big of a deal, and I don’t get fogging up. It may fog for a minute when we toss a ton of water on the rocks, but clears up very quick.
My opinion: prolonged moisture on window glass is a symptom of Wet Noodle Syndrome.
I am in the design stage of building a sauna on Bowen Island in BC Canada and am trying to figure out the best type of glass to use as a window in part of one of the walls.
In this article you said: “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. ”
Are you meaning laminated glass or insulated with airspace between?
Thanks,
Roland
Hi Roland..
I’ll try to make this easy. And this isn’t “definitive” but my experience.
1. Smaller window: (say, a transom window around 20″x42″).. go with single pan tempered. 1/4″ or 3/16″ ish.
2. Larger window: (like you see in those Windex Saunas, around 7’x6′)… order a thermally insulated multiple pan window from a glass company.
I’m sending you an email. I will be out to your area for a sauna conference in January (2025).
Hi Glenn,
I am rather proud of the candle window I built. I purchased an 18″x18″ piece of 1/4″ tempered glass from a local glass shop. For the frame I used some cedar 2x4s, planed down to about 1.25″ wide using a 100 year old rabbet plane. I needed them to be a little narrower to accommodate the wooden sash plane I wanted to use. The sash plane has two blades, one makes the decorative trim on the front, while the other is straight and cuts down the back for the glass. Once I sharpened the blades, it slid along like butter and easily cut all four sides. Not bad for a plane made between 1832 and 1847!
When you’ve recommended a dual pane tempered insulated panel, is the final thickness of the window 1/4 or each of the individual panes 1/4 plus a gap? If so what size gap?
Scotty, you can go 1/4″ single pane or for “big wow” windows, go double pane insulated via a glass company. The big wow windows are like the ones we see in modern new houses. big glass.
Hi Glenn, this is all very helpful, thank you! Im hoping to build a 24″ tall by 45″ wide window. do you think single pane tempered would be sufficient? Or do I need the insulated glass there? I live in NY state. gets cold.
i’d go single pane for this size.. any larger, insulated.
Hi Glenn,
We have an existing Marvin awning window (roughly 30×15) with pine frame in the room we are converting into a sauna. I saw in the earlier comments that you think that’s fine, but what about the painted finish? It’s currently painted white and will need to be freshened up post construction. Is there a non-toxic paint that we should use or is it best to sand off all of the old paint and expose the raw wood?
Hi Glenn,
Local glass place didn’t understand: “1/4 inch, tempered glass, double pane”
They said 5/8″ would be minimum thickness for double pane (1/8″ for each pane, plus space inbetween)
Did you mean each pane should be 1/4″? so total thickness of ~1″?
if the glass isn’t big glass, single pane is just fine.
52″ x 24″ – I was thinking double pane to better insulate
(and 22″x18″ and 12″x12″ Maybe single pane for the 12×12, double pane for the others)
Hi Glenn, in the design phase in Upstate NY… and there is a lot of talk of glass here
but i just read that if you go double pane, that the argon gas can expand dramatically
due to the extreme heat causing the seal to break, not good… or worse, shatter the tempered glass.
Does this ring true, or is this a freak situation?
I am planning a 36″x 48″single casement. You seem to think at this size it should be insulated?
Gas… no Gas? CG
I have been researching this, and learned that double paned windows with certain gases, like argon, are not recommended and can shatter the glass. I spoke to a local glass company and they can make any double-paned tempered window. However, they didn’t know what to think about potential fogging in-between – the air space will not be sealed like an argon sealed window is. I’m worried about what happens when moisture inevitably gets inside the space (a steamy sauna), and then the window cools down to zero or below, as it does here in Minnesota. Wouldn’t you get ice forming in between the panes?
Bottom line, how do I tell my local glass company to build a double-paned tempered window?
Hi Paul:
General rule:
– a smaller window (up to about 2’x3′): single pane tempered.
– a larger window (those big wow instagram looking windows): Contact Marvin or window company for insulated double or triple pane low e glass window.
You got it!
Hi Glen,
Is there a limit to the size of glass window? Could I have a tempered double glazed window floor to ceiling (7ft) and 6ft wide?
Would the winter effects of 0C on the outside and 80-100C inside be critical or would two units side by side be advantageous?
Ashley,
More and more, folks are choosing mega glass windows for their hot rooms. 7’x6′ is not unreasonable if, as you describe, tempered double glazed, insulated fixed window.
My bent is to be a bit more conservative with the glass.. you can keep it wide and panoramic, but i like coming off the floor to hip or belly button height off the ground. Even if looking out to a rolling Cotswolds hillside, the viewing angle from the bench is pretty much the same “ahhhh”. You just don’t see the sheep walking right in front of the sauna, which may be a good thing, and you get the thermal goodness for sure, which is a great thing.
And two units side by side: you loose the “big wow” but you gain stability of the structure and not so costly, especially if one of the windows cracks or fails.
Good day
We are in the throws of building an outdoor sauna with an outdoor shower.
The sauna is 8 x 6′ and will be built just off the deck of our house. We have a window opening of 3 x 6′. We live in Nelson, BC so we get a fair amount of snow and it can dip down to about -15 ( not for long or that often these days).
For a window of that size can we use 8mm tempered single pane, bronze tinted? Or do we need to go with a double pane thermal insulated window.
Your advise would be greatly appreciated! Thank you, Marjie
For that size, I’d be sizing up a window company in your area for insulated glass fixed window. Wood clad interior.