Sauna Windows — Tempered Glass for Custom Builds

Adding a window to your sauna brings in natural light, makes the space feel more open, and gives your build a finished, premium look. Every window on this page uses tempered glass rated for sauna temperatures (up to 470°F) and the thermal shock of water splashing against hot glass. We carry frameless single-pane panels, framed dual-pane windows, round porthole-style windows, and custom-sized glass for walls and large openings. Free shipping on every order.

Looking for glass sauna doors instead? See our glass sauna doors. For custom glass wall panels in any size or tint, see our full glass windows & walls collection including custom-cut options.

Window Styles We Carry

Frameless single-pane tempered glass (14" wide) — The most popular option for DIY custom builds. These are bare tempered glass panels designed to fit between standard 16" on-center wall studs with no frame — you build your own wood frame on site to sandwich the glass in place. Available in multiple heights and two glass types: clear tempered glass for maximum light, and MirroGlass for one-way privacy (mirror finish on the exterior, see-through from inside). Single-pane construction eliminates the risk of condensation between panes that can occur with dual-pane windows when seals fail from repeated heat cycling.

Round tempered glass windows (14"–30" diameter) — Porthole-style round windows that add a distinctive design accent to any sauna wall. Same frameless single-pane tempered glass as the rectangular panels — you build the circular frame on site. Available in clear and MirroGlass (privacy mirror) options. Round windows are a popular feature in barrel saunas, cabin saunas, and traditional Finnish-style builds.

Framed dual-pane windows in cedar (12×39" and 27×42") — Pre-framed windows with double-pane bronze tempered glass set in a cedar wood frame. The dual-pane construction with an air gap provides better insulation than single-pane, and the bronze tint gives a warm, amber-toned light inside the sauna while reducing visibility from outside. The cedar frame matches cedar wall cladding. Two sizes available for different wall areas.

ProSaunas framed dual-pane windows in hemlock — Pre-framed dual-pane tempered glass windows in a hemlock wood frame. Available in standard (17-5/8" × 31") and large (25-5/8" × 37-5/8") sizes. These are professionally crafted, ready-to-install windows — just set them into your rough opening, shim, and secure. Hemlock frames pair well with hemlock wall cladding.

Thermory black aspen framed windows (19.3×35" and 19.3×74.4") — Premium single-pane sauna windows in a black-stained aspen frame from Thermory. The dark frame creates a striking modern contrast against lighter wall cladding, especially thermo-aspen or natural aspen walls. The 19.3×74.4" size is a near-full-height window that functions almost like a sidelight panel next to a door.

Single Pane vs. Dual Pane

Single pane — One layer of tempered glass. The advantage in a sauna is reliability — there's no sealed air gap between panes that can fail from the constant heat cycling (heating to 180°F+ then cooling to room temperature, repeated daily). When dual-pane seals fail, you get permanent condensation between the panes that can't be cleaned. Single-pane windows will get some condensation on the interior surface during use (same principle as a cold glass of water on a humid day), but it wipes off and doesn't affect the glass long-term.

Dual pane — Two layers of tempered glass with an insulating air gap. Better thermal insulation than single pane, meaning less heat loss through the window. The tradeoff is the long-term risk of seal failure from heat cycling. Our dual-pane windows use quality seals designed for temperature extremes, but in a sauna environment that heats and cools daily, single pane is the lower-maintenance option for long-term durability. Dual pane is the better choice if heat retention is a top priority (cold-climate outdoor builds, large window areas) and you're willing to accept the seal-life tradeoff.

Clear, Bronze & MirroGlass — Which Glass Type?

Clear glass — Maximum light transmission and full visibility in both directions. The default choice for indoor saunas where privacy isn't a concern, or any build where you want the most natural light inside.

Bronze tinted glass — A warm amber/brown tint that softens the light and reduces visibility from outside. Provides some privacy during daytime use while still letting plenty of light in. The warm tone complements cedar and other natural wood interiors nicely. Available in our cedar-framed dual-pane windows.

MirroGlass (mirror privacy) — One-way privacy glass with a mirror-like finish on the exterior side and see-through visibility from the interior side. Works on the principle of light-level difference — the brighter side (outside) sees a mirror, the dimmer side (inside the sauna) can see out. Provides excellent daytime privacy for outdoor saunas where neighbors or passersby could otherwise see inside. Note that the privacy effect reverses at night if the sauna interior is lit and the exterior is dark.

Installation Tips

Frameless glass panels are installed by building a wood frame (interior and exterior pieces) that sandwiches the glass in your rough wall opening. Apply a bead of clear silicone caulk around the opening where the glass will sit, press the glass into position, and secure the interior frame. Small foam spacers under the glass keep it centered. Our product pages include detailed installation instructions.

Pre-framed windows (ProSaunas, cedar-framed, Thermory) install like standard windows — set the framed unit into your rough opening, shim for plumb and level, and secure the frame to the studs. Check each product's rough opening dimensions before framing.

Important: tempered glass cannot be cut, drilled, or ground after manufacturing — it will shatter. All sizing must be final before ordering. If you need a non-standard size, our custom tempered glass panels can be ordered in any dimension.

Remember that glass is a poor insulator compared to an insulated wall. Every window you add reduces your sauna's thermal efficiency slightly. Make sure your heater is sized to account for glass surface area — our heater sizing calculator includes a glass adjustment. For full build planning, see our A–Z Custom Sauna Room Guide and our guide to adding a glass wall to your sauna.

Frequently Asked Questions

Can I use regular window glass in my sauna?

No. Only tempered glass is safe for sauna use. Standard annealed glass can crack from thermal shock and breaks into dangerous sharp shards. Tempered glass is rated for temperatures up to 470°F, handles thermal shock (cold water splashing on hot glass), and breaks into small blunt pieces if it ever does shatter. Building codes require safety-rated glass in sauna enclosures.

Will adding a window make my sauna too cold?

A single standard-sized window has a modest impact on heat retention in a well-insulated sauna with a properly sized heater. Multiple large windows or a full glass wall will have a more significant effect and should be factored into your heater sizing. Use our heater sizing calculator which accounts for glass surface area in its recommendations.

Should I choose single pane or dual pane?

For most residential saunas, single pane is the simpler, more reliable long-term choice — no seal failure risk. Choose dual pane if you have large glass areas in a cold-climate outdoor build where the extra insulation will make a meaningful difference. See the comparison section above for details.

Can I get a custom size?

Yes. Our custom tempered glass panels can be ordered in any size or tint for glass walls, oversized windows, or non-standard openings. Contact us at (360) 233-2867 for a custom glass quote.

What about condensation?

Some condensation on the interior surface of single-pane windows is normal during sauna use — it's the same effect as moisture forming on the outside of a cold drink. It doesn't damage the glass and typically diminishes as the sauna reaches full operating temperature. Wipe it down if it bothers you. With dual-pane windows, the concern is condensation between the panes from seal failure — see the single vs. dual pane section above.

Learn More

Our guide to adding a glass wall to your sauna walks through the full planning and installation process. Our complete sauna door guide covers glass types, tempered vs. insulated, and code requirements in detail. Questions? Call or text us at (360) 233-2867.

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