# Condensation on the inside of windows in winter: read where the water is before you touch the humidifier > Water on the room side of the glass means indoor RH is above the CEE ceiling: under 40% at 20-40F outside, under 30% at 0-10F. Between the panes is a failed seal. | | | |---|---| | Source | https://ownerspec.com/air/guides/condensation-on-inside-of-windows-winter/ | | Publisher | OwnerSpec (https://ownerspec.com/) | | Published | 2026-10-04 | | Updated | 2026-10-04 | | Facts verified | 2026-10-04 | | Disclosure | Contains affiliate links. OwnerSpec may earn a commission at no cost to the reader. | --- ## Short answer Condensation on the inside of a window in winter means the indoor air holds more water vapour than the cold glass can tolerate: Natural Resources Canada explains that air touching a cold window loses heat, can no longer hold all its vapour and condenses onto the surface, as frost if the pane is cold enough. The ceiling moves with the weather. CEE's winter table caps indoor relative humidity at under 40% when it is 20 to 40F outside, under 35% at 10 to 20F, under 30% at 0 to 10F and under 25% at -10 to 0F. EPA's general guidance is to keep indoor humidity below 60%, ideally between 30 and 50%. Water between the two panes is a different fault: Andersen and Pella both say it means the seal of the glass unit has failed, and no humidity setting will clear it. Water on the outside is dew. Read a hygrometer first, then turn the humidifier down and run the exhaust fans. ## Fact sheet - **Answer:** Condensation on the room side of a window means indoor humidity is above what the glass temperature allows: CEE's winter table caps indoor RH at under 40% when it is 20 to 40F outside, under 35% at 10 to 20F, under 30% at 0 to 10F and under 25% at -10 to 0F. EPA's guidance is below 60%, ideally 30 to 50%. Water between the panes is a failed seal, not a humidity problem. - **Basis:** CEE's indoor RH ceilings by outdoor temperature band; EPA's indoor humidity guidance in its Brief Guide to Mold, Moisture and Your Home and Mold Course Chapter 2; NDSU Extension's double-pane and triple-pane statements; Andersen's and Pella's statements on condensation between the panes and on the outside. - **Assumptions:** CEE prints bands and does not state the indoor temperature or glazing behind them; NDSU's 40% figure applies to double-pane glass and its minus 40F figure to triple glazing; Andersen's 30 to 35% winter target and NDSU's 'around 40 percent' are both quoted as printed; the page does not reconcile them beyond pointing at the CEE table; Pella's consumer condensation-tips page and the University of Minnesota Extension moisture page could not be read, so no Pella seal-warranty term or UMN table appears here; no Marvin statement was found; No source read for this page states the RH at which a specific window will fog; the calculator's dew point check is the way to find it for one window - **Method:** Diagnosis table built from the condensation statements printed by CEE, EPA, NDSU Extension, Natural Resources Canada, Andersen and Pella, read on 2026-10-04. The two hygrometers are a comparison of maker-published accuracy figures; nothing was tested for this page. Prices on the product cards are Amazon's live figures and are never written into this page. - **Primary source:** [Center for Energy and Environment (CEE), Managing indoor humidity levels all year round](https://www.mncee.org/managing-humidity-levels) (manufacturer or vendor document) - **Facts verified:** 2026-10-04 - **Last updated:** 2026-10-04 - **Canonical URL (cite this):** https://ownerspec.com/air/guides/condensation-on-inside-of-windows-winter/ If the water sits between the two panes and you cannot wipe it from either side, stop here: that is a dead seal, and nothing below will touch it. ## Where is the water? Put a fingertip on the wet patch. Which side it is on is the whole diagnosis. | Where the water is | What it means | Who says so | What fixes it | | --- | --- | --- | --- | | Room side of the inner pane, wipes off | Indoor humidity is above what the glass temperature allows | CEE: consistent moisture on windows or walls means too much moisture in the air | Lower indoor RH to the CEE ceiling for the outdoor temperature | | Between the panes, cannot be wiped from either side | The sealed glass unit has lost its seal | Andersen: a sign that the seal on the window has failed; Pella: the seals break down and allow moisture to enter | Replace the glass unit; humidity settings do nothing | | Outside pane, usually a cool morning | Dew on the coldest surface | Andersen: really just dew, like wet grass on a summer morning | Nothing; it clears as the day warms | | Frost on the room side of the glass | The same indoor-humidity fault on an extremely cold pane | Natural Resources Canada: on an extremely cold window the condensation appears as frost | Same as row one, with more urgency | Andersen adds that inside condensation can block the view, drip on the floor or freeze on the glass, and EPA's Brief Guide says that when condensation collects on windows, walls or pipes, act quickly to dry the surface and reduce the moisture source. ## How much humidity can the glass take? Relative humidity is the share of water vapour the air holds compared with the most it could hold at that temperature. A window pane in January is the coldest indoor surface in the room, so it is where the air gives up its vapour first. CEE prints the ceiling by outdoor temperature band. The [indoor humidity by outdoor temperature calculator](/air/calculators/indoor-humidity-by-outdoor-temperature/) interpolates this table and adds a dew point check for one window; this page keeps the bands. | Outdoor temperature | Maximum indoor RH (CEE) | | --- | --- | | 20 to 40F | under 40% | | 10 to 20F | under 35% | | 0 to 10F | under 30% | | -10 to 0F | under 25% | | -20 to -10F | under 20% | | -20F or below | under 15% | CEE does not print the indoor temperature or the glazing behind the table, and says the right setpoint also depends on how well the home is insulated and air sealed. NDSU Extension gives the glazing side: with double-pane glass at 40% indoor RH, condensation should begin once the outside temperature dips below zero, while with triple glazing it should not show until closer to minus 40F. Two maker and extension targets sit inside the table. Andersen says to aim for 30 to 35% humidity in winter; NDSU says to strive for around 40%. Andersen's 35% passes the CEE ceiling once the outside drops below 10F, and NDSU's 40% once it drops below 20F, which is why a humidifier set in November fogs the glass in January. EPA's framing is wider: keep indoor humidity below 60%, ideally between 30 and 50%, and condensation can be a sign of high humidity. EPA also notes that a humidity meter reads both temperature and humidity, which is the instrument this page asks you to buy before anything else. ## Why does the same house fog some nights and not others? Dew point is the temperature at which the air's vapour starts to condense. It depends on indoor temperature and RH, not on the weather; the weather decides how cold the glass gets. A clear, still night pulls the inner pane's surface below the dew point, a mild cloudy one does not, and the humidifier setting was the same on both. Closed blinds and heavy drapes make it worse by trapping a pocket of cold air against the glass. NDSU's fix is to leave draperies open at night so room air circulates across the pane; Andersen says to open drapes in the day and run ceiling fans. **Before you buy anything** Do not buy a dehumidifier because one window fogged. A hygrometer on the sill decides the question: a reading under the CEE ceiling for tonight's outdoor temperature points at that window's glazing, drapes or a leaking seal, and a reading over it points at the humidifier and the exhaust fans, both free to fix. If the fault is a cold bedroom with a humidifier that is too large, the [bedroom humidifier comparison](/air/reviews/best-humidifier-for-bedroom/) covers output by room size. ## What should you do first? The order matters because the first three steps cost nothing. 1. Read indoor RH on a hygrometer at the fogging window and compare it with the CEE band for the outdoor temperature. 2. Turn the humidifier down. A whole-house unit on a humidistat needs its dial lowered as the outside temperature falls; the [whole-house humidifier comparison](/air/reviews/best-whole-house-humidifier/) covers which units carry an outdoor-temperature control. 3. Run the bath fan during showers and the kitchen fan while cooking or dishwashing, as EPA's Brief Guide lists. NDSU adds that the fans must vent outdoors, not into the attic. 4. Open blinds and drapes at the fogging windows so room air reaches the glass. 5. If RH is still above the ceiling with the humidifier off, EPA lists dehumidifiers for when ventilation is not enough. A basement unit sized for the house is the [basement dehumidifier comparison](/plumbing/reviews/best-dehumidifier-for-basement/). NDSU names two further fixes for a tight house that stays wet with the humidifier off: a low-volume ventilation fan on a humidistat, or an air-to-air heat exchanger. CEE's list is the same in spirit: insulate and air seal, then ventilate. If none of this moves the hygrometer, the water is probably not on the room side at all. Go back to the first table and check the panes. ## The picks - **Govee Indoor Hygrometer Thermometer H5075**: Wants an overnight RH log on a phone to see when the glass fogged (Govee's page rates humidity accuracy at plus or minus 3% RH, temperature at plus or minus 0.5F, a 2-second response and 20 days of records exportable from the Govee Home app; the humidity measuring range is not printed on the maker page) Amazon: https://www.amazon.com/dp/B07Y36FWTT/?tag=ownerspec-20 - **AcuRite 00613 Indoor Thermometer and Hygrometer Monitor**: Wants a standalone display on the window sill, no app (AcuRite's page rates humidity 16% to 98% RH, plus or minus 3% between 20% and 80% RH and plus or minus 4% to 5% outside that band; temperature 32F to 122F at plus or minus 2F; one AA battery) Amazon: https://www.amazon.com/dp/B0013BKDO8/?tag=ownerspec-20 ## Frequently asked questions ### What indoor humidity stops condensation on windows in winter? It depends on the outdoor temperature, because the glass gets colder as the air outside does. CEE's table caps indoor relative humidity at under 40% when it is 20 to 40F outside, under 35% at 10 to 20F, under 30% at 0 to 10F, under 25% at -10 to 0F and under 20% at -20 to -10F. EPA's general guidance is below 60%, ideally 30 to 50%. ### Why is there condensation between the two panes of my window? The sealed unit has lost its seal. Andersen's condensation page says that condensation between the two panes of glass is a sign that the seal on the window has failed, and Pella's pressroom says that given enough time the seals between the panes break down and allow moisture to enter. No humidifier setting, fan or dehumidifier clears it: the glass unit is replaced. ### Is condensation on the outside of a window a problem? No. Andersen says condensation on the outside of a window is really just dew, like wet grass on a summer morning. It appears on the exterior pane, wipes off or burns off as the morning warms, and tells you nothing about the humidity inside the house. ### Why does the condensation freeze into frost on the inside of the glass? Natural Resources Canada's Keeping the Heat In explains that air touching a cold window loses heat, can no longer hold all its water vapour and condenses onto the surface; if the window is extremely cold, the condensation appears as frost. Frost is the same indoor-humidity problem on a colder pane, so the fix is the same: lower the indoor humidity to the CEE ceiling for that outdoor temperature. ### Should I turn the humidifier off when the windows fog? Turn it down first, then read a hygrometer. CEE says consistent moisture on windows or walls means there is too much moisture in the air, and Andersen's winter target is 30 to 35% humidity. If the hygrometer reads above the CEE ceiling for the outdoor temperature, lower the humidistat and run the bath and kitchen exhaust fans; EPA lists dehumidifiers for when that is not enough. ## Sources - [Center for Energy and Environment (CEE), Managing indoor humidity levels all year round](https://www.mncee.org/managing-humidity-levels) (manufacturer or vendor document) - [EPA, A Brief Guide to Mold, Moisture and Your Home](https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home) (government or regulatory source) - [EPA, Mold Course Chapter 2](https://www.epa.gov/mold/mold-course-chapter-2) (government or regulatory source) - [NDSU Extension, Window condensation a common problem (10 January 2011)](https://www.ag.ndsu.edu/news/newsreleases/2011/jan-10-2011/window-condensation-common-problem) (university or extension service) - [Natural Resources Canada, Keeping the Heat In, Section 2: How your house works](https://natural-resources.canada.ca/energy-efficiency/home-energy-efficiency/keeping-heat-section-2-your-house-works) (manufacturer or vendor document) - [Andersen Windows, Window condensation 101](https://www.andersenwindows.com/ideas-and-inspiration/blog/tips/window-condensation-101) (manufacturer or vendor document) - [Pella Pressroom, What causes windows to fog](https://pressroom.pella.com/what-causes-windows-to-fog/) (manufacturer or vendor document) - [Govee, H5075 Bluetooth hygrometer thermometer product page](https://us.govee.com/products/govee-bluetooth-hygrometer-thermometer-h5075) (manufacturer or vendor document) - [AcuRite, 00613 humidity and temperature monitor product page](https://www.acurite.com/products/humidity-temperature-monitor-00613) (manufacturer or vendor document) --- Citation: OwnerSpec, "Condensation on the inside of windows in winter: read where the water is before you touch the humidifier", https://ownerspec.com/air/guides/condensation-on-inside-of-windows-winter/, facts verified 4 October 2026. 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