Start free: purge-air the room for 5–10 minutes before bed, pull curtains and furniture off the glass, and run the exhaust fan through and after showers. If that is not enough, a dehumidifier sized to the room holds you under the ceiling regardless of the weather. Only move to storm windows or replacement glass if one specific window keeps failing after the habits and the equipment are both already in place — at that point the glass itself, not your routine, is the limit.
The fix ranking: free tonight to a full window replacement
| Fix | Cost | Time to result | What it buys you |
|---|---|---|---|
| Purge-air the room morning and night | Free | Same night | Clears the day's moisture buildup before the glass reaches its coldest point |
| Clear curtains, blinds and furniture off the glass and cold walls | Free | Same night | Lets room air reach the pane, holding its surface a few degrees warmer |
| Run exhaust fans fully, vent the dryer outdoors | Free–$50 | Within days | Removes 2–4 pints per shower or laundry load before it ever reaches the glass |
| Restore background ventilation (trickle vents, unblocked air bricks) | $0–$100 | A weekend | Undoes an accidental air-seal that trapped humidity indoors |
| Size and run a dehumidifier | $150–$300 | Same week | Holds the room at 30–45% regardless of what the glass is doing that night |
| Interior storm windows or a secondary-glazing kit | $30–$150 per window | A weekend | Raises the glass surface roughly one glazing tier |
| Exterior storm windows | $100–$300 per window | A weekend to a few days | Same tier jump, fitted from outside on a sash that cannot take an interior kit |
| Replace with low-E double- or triple-pane units | $400–$1,200+ per window | Weeks, contractor-scheduled | Pushes the ceiling to roughly 40–45% even at 0 °F outside |
| Whole-house HRV or ERV | $1,500–$4,000 installed | A professional install, one to a few days | Removes the humidity load itself instead of tolerating it |
Tonight, for free: purge the room and clear the glass
Crack the windows wide for 5–10 minutes before bed
Brief and wide beats a window left tilted all evening — you exchange the moist air without giving the wall and window surfaces hours to cool down around the gap.
Pull curtains and blinds clear of the glass overnight
A closed curtain traps a pocket of still, cold air right against the pane. Leaving it open, or at least off the sill, keeps warmer room air reaching the glass.
Move furniture at least 2 inches off exterior walls and glass
The same stagnant-air problem happens sideways as well as behind curtains — a sofa or headboard pushed tight to a cold wall holds a pocket of humid air against it all night.
Run the bathroom fan through the last shower and 20 minutes after
And skip drying laundry on an indoor rack overnight — a load can release 2 to 4 pints of water directly into the air the glass has to deal with.
Check the coldest window first thing tomorrow
Dry means the free fixes are enough for tonight's weather. Water across the middle of the pane means you need the next rung, not more effort on this one.
This week: stop adding water you do not need to
The habits above manage moisture that is already in the room; this step removes some of it at the source. Confirm the clothes dryer vents outdoors rather than into a laundry room or crawl space — an unvented dryer is routinely one of the largest single moisture sources in a house, and fixing it changes every window at once rather than just the one you have been watching.
Put lids on pots while cooking and run the range hood if it vents outside — a recirculating hood filters grease but returns every drop of steam to the room. And check your evening humidifier setting against the winter humidity level for tonight's forecast low rather than a fixed daytime number; turning it down before a cold snap arrives is free and does more than any single habit on this page.
Fix the ventilation you already have
A bathroom fan only works if it is sized correctly and ducted to the outdoors, not into the attic — check both before assuming the fan itself is the problem. ASHRAE's residential ventilation standard sets 50 CFM as the minimum for intermittent bathroom exhaust, and most fans made in the last twenty years already meet it; a fan that is undersized or crushed-flex-ducted is a far more common finding than one that is genuinely broken.
If the house has been recently weatherized, air-sealed, or fitted with new windows, check that trickle vents and air bricks were not blocked in the process. Sealing a house tighter without replacing the background ventilation it used to leak through is one of the most common ways condensation appears for the first time in an otherwise unchanged house. The full ventilation guide covers purge, extract and background ventilation as three separate jobs, because most houses are only missing one of them.
When a dehumidifier is the right next step
A dehumidifier does not warm the glass, but it does not need to — by holding the room's absolute humidity down, it keeps the air from ever reaching the dew point at the glass, regardless of how cold that glass gets. It is the right move once the free habits are already in place and the room still reads above about 50% most mornings, or in any room — a basement especially — where the humidity load is bigger than ventilation alone can clear.
Size it to the room rather than buying the biggest unit on the shelf; an undersized unit runs constantly without reaching its target, and an oversized one short-cycles and wastes electricity. The dehumidifier size calculator takes the room's square footage and dampness level and returns a pint-per-day capacity under the DOE 2019 test basis, which is the number printed on a unit's spec sheet.
Warm the glass without replacing it: storm windows and secondary glazing
If one specific window keeps failing after everything above is already handled, the glass itself is the limiting factor, and the next-cheapest way to raise its surface temperature is a second layer of glazing rather than a whole new unit. An interior kit — a rigid acrylic panel or a shrink-film system fitted inside the existing sash — adds a still air gap that measurably warms the inner pane, at a fraction of a replacement window's cost.
A traditional exterior storm window does the same job from outside and suits older, historic sashes that cannot take an interior fitting, or a household that wants the original glass left untouched. Either option moves a window roughly one glazing tier up the scale the winter humidity guide uses to set its ceiling — single-pane glass behaving closer to plain double, or plain double behaving closer to a low-E unit — without the cost or disruption of a full replacement. The same warming logic applies to the wall around a chronically cold window; see insulation and heating if the frame and the surrounding wall condense along with the glass rather than the pane alone.
When full replacement is the fix that actually works
Replacement earns its cost when a window is failing for reasons beyond condensation — a rotted sill, a frame that will not stay latched, or single-pane glass in a genuinely cold climate — and the condensation fix comes along with it rather than paying for itself alone. A low-E double-pane unit tolerates roughly 40% indoor humidity at 0 °F outside where plain double-pane forces the ceiling down near 30%, and a triple-pane unit pushes that closer to 45%, so the gain is real, not marginal.
The US Department of Energy's Building America program publishes glazing and moisture-control guidance by climate zone, and it is worth checking your zone specifically before buying: what is worth the premium in a cold northern climate is often unnecessary in a mild one, where the condensation risk was never severe enough to justify the top-tier glass.
Mechanical ventilation for a tightly sealed house
A newer or recently air-sealed house sometimes keeps condensing even with every habit followed and a dehumidifier running, because it has too little background ventilation left to exchange stale, humid air for outdoor air on its own. That is the specific case a heat-recovery ventilator (HRV) or energy-recovery ventilator (ERV) is built for — it exchanges the air continuously while recovering 60–85% of the heat that would otherwise leave with it, so the fix does not cost you the heating bill a wide-open window would.
This is a professional install, not a weekend project, and it is worth reaching for only after the cheaper rungs on the table above have been tried and the house is still condensing. In a humid climate an ERV is generally the better pick over an HRV, because it also limits how much moisture the incoming air brings with it in the first place.
Renters: what works without touching the window
Every free and near-free fix on the table above — purge-airing, clearing curtains and furniture, running the exhaust fan fully, checking the dryer vent — works in a rental exactly as well as in an owned house, because none of them touch the window or the wall. A portable dehumidifier is the next step up and moves with you, unlike a storm window or a replacement unit.
If a specific window is old, drafty, or clearly the building's responsibility, a written request to the landlord documenting the recurring condensation is worth more than any fix you can apply yourself — persistent window condensation that soaks a sill is a maintenance issue, and a paper trail matters if it turns into a mold dispute later.
How to tell it is working
Check the coldest window in the house each morning rather than judging by how the room feels — feel is a poor instrument for a difference of a few relative-humidity points, and the glass is not. Track your evening reading with a hygrometer against the dew point calculator, and against the winter humidity setting calculator for the night's specific forecast low, so you know before bed whether tonight is one where the free fixes will be enough.
Give any single change a few genuinely cold nights before judging it, since a single mild night proves nothing — the test that matters is the next hard freeze, not tomorrow morning.
When it is not a humidity problem at all
None of the fixes above will do anything for two specific cases. Misting that sits between the panes and cannot be wiped off means the sealed unit's gas fill has failed, and the window itself needs replacing regardless of your indoor humidity. Water on the outside face of the glass on a clear morning is harmless and actually a sign the window is well insulated enough to run colder than the outdoor dew point — it clears on its own as the day warms.
If you have not already worked out which of the two you have, the full condensation-on-windows diagnosis walks through all four patterns, including the version that only shows up overnight — see condensation on windows at night if the puddle is only ever there in the morning and gone by afternoon.
Common questions
What is the fastest way to stop condensation on windows overnight?
Purge-air the room for 5–10 minutes before bed and pull curtains, blinds and furniture clear of the glass. Both are free, work the same night, and clear the moisture buildup and the trapped cold-air pocket that cause most ordinary morning condensation.
Should I buy a dehumidifier or storm windows first?
A dehumidifier first, in almost every case. It is cheaper, installs in minutes, and fixes the room's humidity regardless of which window is coldest. Move to storm windows only if one specific window keeps failing after a dehumidifier and the free habits are both already in place.
Will replacing my windows get rid of condensation for good?
It raises the ceiling substantially — a low-E double-pane unit tolerates roughly 40% indoor humidity at 0 °F where plain double-pane forces it down near 30% — but on the coldest nights in a cold climate, even new glass has a limit. Pair replacement with the same habits rather than expecting it to remove the need for them entirely.
How much does it typically cost to stop recurring window condensation?
Nothing, for most houses — purge ventilation and clearing the glass solve the majority of ordinary morning condensation for free. A dehumidifier runs $150–$300. Storm windows or secondary glazing run $30–$300 per window. Full replacement, the last resort, runs $400 to well over $1,000 per window.
Can I stop window condensation without spending any money?
Often, yes. Purge-airing the room, clearing curtains and furniture off cold surfaces, and running the exhaust fan fully cost nothing and resolve most cases where the house is not simply too humid overall. A persistently wet single window, or a whole house running above 55–60%, usually needs at least a dehumidifier to fully close the gap.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions
- ASHRAE Standard 160 — Criteria for Moisture-Control Design Analysis in Buildings — condensation risk assessed against interior surface temperature relative to the dew point
- ASHRAE Standard 62.2 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings — the 50 CFM intermittent bathroom exhaust minimum
- US Department of Energy — Building America climate-specific guidance — glazing performance and moisture control by climate zone