Will double glazing fix condensation on bedroom windows?
Double glazing cuts condensation, but it does not remove the moisture. What glazing changes, what only ventilation changes, and what to do about a wet bedroom window.
By the NZ Double Glazing team
Key takeaways
- Condensation needs two things: moisture in the air and a cold surface. Double glazing warms the surface; it does nothing about the moisture.
- EECA lists reducing condensation and mould among the benefits of window insulation, alongside a warmer, drier home.
- A bedroom is the worst room for it: two people breathing overnight behind a closed door, with the heating off.
- If condensation moves from the glass to a colder wall or wardrobe after you double glaze, the moisture source is the thing that needs fixing.
- We publish no pane temperatures or dew points for your house, because no source we trust gives a figure that would apply to it.
It reduces it, often dramatically, but it does not remove the cause. Condensation forms when moist indoor air meets a surface cold enough for that moisture to turn back into water. Double glazing makes the inside pane warmer, so it condenses less. The moisture is still in the room, and if there is a colder surface somewhere it will find it.
Why the bedroom window is always the wet one
Bedrooms combine everything condensation likes. Two people breathe out moisture for eight hours. The door is shut, so that moisture cannot disperse. The heating is off overnight, so the room and the glass are at their coldest just before dawn. Single glazing gives that air the coldest surface in the house to condense on, which is why you see it on the window first.
What double glazing changes
A sealed unit puts a still layer of air or gas between two panes, so the inside pane sits much closer to room temperature than a single pane does. EECA lists a warmer home, lower heating bills and reduced condensation and mould among the benefits of insulating windows. In practice that usually means a bedroom window that is dry most mornings instead of running.
What it does not change
- The amount of moisture you put into the air: breathing, showers, unflued gas heaters, drying washing indoors, cooking without an extractor.
- Whether that moisture can get out. A closed bedroom with no trickle vent or extract has nowhere to send it.
- Other cold surfaces. Uninsulated exterior walls, the back of a wardrobe against an outside wall, and window reveals can all be colder than a new double-glazed pane.
- Rising damp or a leak. If there is a water source, the window was never the problem.
The honest sequence to try
- Ventilate deliberately. Open windows for a few minutes each morning, use the extractor for showers and cooking, and dry washing outside or in a vented dryer.
- Warm the room a little, rather than a lot. A room that never gets cold does not reach the temperature where the moisture condenses.
- Insulate the ceiling and underfloor first if they are not done. EECA's Warmer Kiwi Homes programme co-funds ceiling and underfloor insulation and heat pumps — it does not fund glazing.
- Then double glaze. It is the step that fixes the cold surface, and it is worth doing; it is just not the first or the cheapest one.
Cheaper things that genuinely help
EECA says closing curtains before dark can save around $80–$90 a year, and that window insulation film kits can reduce heat loss by almost as much as double glazing in some cases. If you are renting, or the budget is not there this year, those are real options and we would rather tell you than sell you a job.
What we will not tell you
We do not publish pane temperatures, dew points or litres of water vapour for your house. Those numbers depend on your occupancy, heating and ventilation, and no source we would cite gives a figure that transfers to an individual home. If you see a site quoting an exact indoor pane temperature for a house it has never visited, treat it carefully.
Questions
Will double glazing stop condensation completely?
Not on its own. It removes the coldest surface in the room, which is usually where you see it, but the moisture is still there. Ventilation and a little heat are what deal with the moisture.
Why did condensation appear somewhere else after double glazing?
Because the moisture had nowhere better to go. Once the glass is warm, the next-coldest surface — an uninsulated wall, a reveal, the back of a wardrobe — becomes the place it collects. That is a sign the moisture source needs attention.
Is condensation between the panes normal?
No. Moisture inside a sealed unit means the seal has failed, and that is a warranty matter. Ask for the manufacturer's warranty on the sealed unit in writing before you buy.
Does low-E glass help with condensation?
Low-E coatings improve the thermal performance of the unit — EECA puts the improvement at up to 30% — so the inside pane runs warmer. That helps, but it is still the same trade-off: warmer surface, same moisture.
Should I fix ventilation before I double glaze?
Try it first, because it is free. Extract showers and cooking, dry washing outside, and air the bedroom in the morning. If the window is still wet after that, the cold surface is the problem and glazing is the fix.
Is there funding for double glazing to fix damp?
Not from Warmer Kiwi Homes. EECA's programme co-funds ceiling and underfloor insulation and heat pumps; glazing is not included. We say so because a lot of sites imply otherwise.
Sources
Published 15 September 2026, last updated 15 September 2026 by the NZ Double Glazing team.