Water on the room side of your glass in winter means your indoor air holds more moisture than that glass can handle at its current temperature. In a home kept at 70 degrees with 40 percent relative humidity, any surface colder than about 45 degrees will sweat. The EPA recommends keeping indoor humidity between 30 and 50 percent. If your home sits inside that band and one or two windows still run wet, the window is usually the cold spot. Window repair with us generally runs $750 to $1,500 per window, and replacement runs $700 to $1,100 per window at the entry tier up to $1,600 to $2,600 for premium lines.
That's the answer. The rest of this guide covers how to tell whether the problem is your windows or your air, how to check the numbers yourself, what Colorado winters add, what each fix costs, and when we will tell you not to call a window company. If you suspect a failing window, start with our window repair page. We work across Denver, Jefferson County, and Boulder County.
One boundary first. This guide covers water on the side of the glass you can touch. Fog trapped between the panes is a failed seal, covered in foggy glass between the panes. Cold air you can feel moving is covered in drafty windows.
What the pattern is telling you
Where the water shows up tells you most of what you need to know.
| What you see | What it usually means | Window or house |
|---|---|---|
| Thin fog along the bottom edge on the coldest mornings, gone by midday | The glass edge is the coldest part of any sealed unit | Usually neither |
| Water running down the glass and pooling on the sill most mornings | Indoor humidity too high for your glass | House first |
| Frost or ice on the inside of the glass | Very cold glass, high humidity, or both | Often both |
| Condensation on one or two windows only | Those units run colder than the rest | Window, likely |
| Water beading on a metal frame | Aluminum conducting cold into the room | Window |
| Worst in bedrooms, bathrooms, and kitchens | Local moisture from breathing, showers, cooking | House |
Why it happens
Warm air holds more water vapor than cold air. When room air touches a surface below its dew point, the vapor turns to water on that surface. In winter, the window is usually the coldest surface in the room. These dew points come from standard psychrometric calculation for a room at 70 degrees.
| Indoor relative humidity at 70°F | Approximate dew point | What it means for your glass |
|---|---|---|
| 30 percent | about 37°F | Only very cold glass sweats |
| 40 percent | about 45°F | Single-pane and failed units sweat on cold nights |
| 50 percent | about 51°F | Decent double-pane may fog at the edges |
| 60 percent | about 56°F | Most windows sweat in cold weather |
Humidity sets the threshold. Glass and frame temperature decide whether you cross it. The right fix depends on which side is off.
Why the common answers are incomplete
"You need new windows." Sometimes. But at 55 percent indoor humidity, new glass will still fog on the coldest nights. Less fog is not the same as fixed.
"Just run a dehumidifier." Good advice when humidity is the issue. It does nothing for one single-pane window or aluminum frame acting like a cold plate while the rest of the room stays dry.
"Colorado is dry, so it can't be humidity." The outdoor air is dry. Indoor air is not always. A humidifier set high, unvented gas appliances, weak bath fans, or a newer, tighter house can push humidity well past what cold glass tolerates. In a dry climate, steady condensation usually points to a moisture source inside the home.
Check the math yourself
- Buy an inexpensive digital hygrometer. Put it in the room with the worst windows, away from the kitchen and bathroom.
- Each morning for a week, record the humidity, indoor temperature, and the overnight low outside.
- On the coldest morning, walk the house and note which windows are wet and which are dry.
How to read it:
- Humidity above 50 percent, most windows wet: a house problem first. Fix the moisture source before spending money on glass.
- Humidity in the 30 to 45 percent range, a few windows wet: those windows run colder than they should. That is a window conversation.
- Humidity in range, every single-pane or aluminum window wet: that construction is doing what it does in a Colorado winter. That points toward replacement, not repair.
What Colorado winters add
Big daily temperature swings. A 50-degree afternoon can drop into the teens overnight. Glass that was dry at dinner is wet at 6 a.m., so many homeowners only ever see it in the morning.
Older housing stock. Denver homes from the 1940s through the 1960s still have single-pane glass, steel casements, and early aluminum sliders. Single-pane runs close to outdoor temperature, and aluminum carries cold straight into the room. More on that era on our Denver page.
Aging double-pane. Units from the 1970s through the 1990s are reaching the end of their seal life across much of the metro. A unit that has lost its gas fill performs closer to single-pane. A window that started sweating this winter after years of staying dry deserves a look.
Intense UV at 5,280 feet. Sun at this elevation breaks down sealants and weatherstripping faster, which chills the sash edge. Our guide to high altitude windows covers what elevation does to sealed glass.
Wind and hail. Foothills wind in Jefferson County wears weatherstripping early. Hail can crack or compromise a sealed unit, and roofing or restoration crews sometimes miss window damage after a storm.
Find out whether it is the window.
Free visit, no trip fee and no diagnostic fee. We check the glass, seals, sash, frame, and sill and give you a written number. Written quotes are good for 30 days.
What it costs when the window is the problem
If your humidity is reasonable and specific windows still run wet, these are the window-side fixes, with replacement prices current as of October 2026. Every replacement quote prices each window on its own line, so you can replace your worst windows first.
| Fix | When it fits | Price |
|---|---|---|
| Window repair: glass unit, weatherstripping, seals, hardware, sash | Sound frame, isolated failure | Generally $750 to $1,500 per window |
| Entry vinyl replacement, retrofit, standard size | Single-pane or aluminum, budget first | $700 to $1,100 per window |
| Mid-range vinyl or composite replacement | Better glass, spacers, and hardware than entry | $1,100 to $1,600 per window |
| Premium fiberglass or wood-clad replacement | Older homes, wood interiors, long service life | $1,600 to $2,600 per window |
| Specialty: bay, bow, custom shapes, oversized | Non-standard openings | $2,600 and up per window |
| Full-frame instead of retrofit | Sill or frame rot, often from years of condensation | Adds about $200 to $300 per window |
| Whole home | Many failing units at once | Most projects $8,000 to $20,000 for smaller homes and $25,000 to $55,000 for larger homes |
Most whole-home projects we price land in the mid-range to premium bands, which is where our $1,500 to $2,000 per window average comes from.
There is no flat rate for repairs, and our $750 minimum applies per job. Price depends on the window, the part, and access, and second-story windows can cost more. When a repair would run past about $1,500, replacing that window is usually the better value, and we will say so. Before any repair starts, you get a full written scope and contract. If we find hidden rot or water damage, we stop, show you, and re-quote if the scope changes.
What our visit covers, and what it does not
What we look at: glass, seals, sash, frame, sill, weatherstripping, and hardware. During the visit we also check for foggy glass, broken glass, and balance problems you may not have noticed. There is no trip or diagnostic fee, and the consultation is free.
What we do not do: diagnose interior humidity or whole-house moisture. If your hygrometer reads high, call an HVAC contractor or a home energy auditor. We would rather tell you that than sell you glass that will not fix it.
We do not warranty repairs. For terms on our installation work, see our warranty page. Manufacturer warranties on the product are separate.
What ignoring it costs you
Light morning fog is harmless. Water sitting on the sill every day all winter is not.
- Sill and frame rot, which can turn a retrofit into full-frame work.
- Mold. The EPA notes that mold needs moisture to grow, and a wet sill is a steady supply.
- Peeling paint, stained drywall, and damp blinds below and around the window.
It happens over several winters, which is why it is easy to ignore until the sill gives under your thumb.
Try these yourself first
- Turn down any humidifier and watch your hygrometer for a few days.
- Run bath fans during and after showers. Use the range hood when you cook.
- Leave blinds and curtains open or gapped at night so warm air reaches the glass.
- Keep furniture away from windows and supply registers clear.
- Wipe sills dry on wet mornings.
- Make sure sash locks engage fully so the meeting rail closes tight.
If humidity is in range, you have done all of this, and a few windows still sweat, a window visit makes sense.
When we will tell you not to hire us
- Humidity is high and every window sweats. Fix the air first.
- The fog is between the panes. That is a seal failure. See foggy glass.
- Someone offered to drill and vent your glass. We do not recommend it. It hides the fog without restoring the seal or gas fill.
- Only a thin edge line on the coldest mornings. That is normal. Keep the sills dry.
Why we handle it this way
Most Denver window companies sell one manufacturer, so every wet window becomes a replacement pitch. We are independent. We source dozens of manufacturers, and the five we know best are Sierra Pacific, ProVia, Milgard, Pella, and Amsco. Nobody upstream cares whether a new window ends up in your wall at all.
Sometimes the answer is a hygrometer and an HVAC call. Sometimes it is one repair. If it is replacement, you get itemized per-window pricing across more than one line, no high-pressure presentation, and a written quote good for 30 days. Installation typically follows two to four weeks after you sign.
When comparing quotes, ask for the NFRC Condensation Resistance rating. The National Fenestration Rating Council scores it from 1 to 100, and higher means better resistance to room-side condensation.
Frequently asked questions
Is condensation on the inside of my windows bad?
A thin line of fog at the glass edge on the coldest mornings is normal. Water that runs onto the sill most days is a problem, because over a few winters it can rot sills and feed mold.
Why are my windows sweating more in the morning than at night?
Colorado overnight lows can fall far below the afternoon high, so the glass is coldest just before sunrise. Bedrooms also gain moisture overnight from breathing.
Why does only one window in the room get wet?
That window is running colder than the others. A failed seal, cracked unit, worn weatherstripping, or aluminum frame are the usual causes.
Will new windows stop condensation completely?
Not always. Modern windows keep the room-side glass warmer, but if indoor humidity is high, even new glass can fog on very cold nights.
Is ice on the inside of my windows a sign of a bigger problem?
Frost on the room side means the glass is below freezing while moisture reaches it. It usually points to single-pane glass, a failed unit, aluminum frames, high humidity, or a mix.
Can my humidifier cause window condensation?
Yes. It is one of the most common causes in Front Range homes. Keep indoor humidity within the 30 to 50 percent band the EPA recommends.
Why did my windows start sweating after I sealed up the house?
Air sealing keeps heat in, but it also keeps moisture in. If ventilation was not improved at the same time, humidity can climb until the glass shows it.
Does Fort Comfort Windows diagnose humidity problems?
No. Our free visit covers the windows themselves. For humidity and ventilation, an HVAC contractor or home energy auditor is the right call.
What should I ask about condensation when comparing window quotes?
Ask for the NFRC Condensation Resistance rating and U-factor on the exact units quoted. Ask whether the quote is retrofit or full-frame, since a rotted sill may need full-frame work.
Find out whether it is the window.
Free visit, no trip fee and no diagnostic fee. We check the glass, seals, sash, frame, and sill and give you a written number. Written quotes are good for 30 days.