Cold fall near windows often feels like a draft. You sit by the window and feel cold air moving along your legs or across the floor. However, outside air does not always come in. During cold spells, warm indoor air cools against cold glass and then sinks downwards.

The short rule is: Cold trap can mainly be solved by better insulating the glass. HR++ glass, triple glass or vacuum glass usually helps better than draft strips alone, because cold trap is caused by a cold glass surface. In this article we explain what cold trap is, how you recognize it and what solutions are available.

What is cold trap?

Cold trap occurs when warm air in the house cools past a cold window. Cold air is heavier than warm air and sinks downward. This creates an air flow past the window towards the floor. That feels like a draft, but it's not the same.

During cold spells, cold outside air does not enter through a crack. The air in the room becomes cold through contact with the window.

Image: schematic cross-section of a window where warm indoor air cools along the glass and sinks to the floor as a cold air flow

Cold falls mainly occur in:

  • single glazing
  • old double glazing
  • large windows
  • windows to the floor
  • sliding doors
  • poorly insulated window frames
  • greenhouses
  • extension with lots of glass
  • cold bedrooms
  • homes without a radiator under the window

How do you recognize a cold spell?

You can recognize a cold spell by a flow of cold air at the window, without there being a clear crack. Signs of cold fall:

  • cold air past the window
  • cold floor at the facade
  • chilly feeling with large windows
  • comfort complaints despite heating
  • window feels very cold
  • curtains sometimes move slightly
  • especially noticeable in winter
  • more complaints with single glazing
  • condensation on the window
  • no obvious crack or whistling sound

When there is a real draft you can feel the outside air through a crack. When there is a cold, the window surface feels cold and cooled air sinks down.

Cold trap or draught?

Cold fall and draft are often confused. Yet the difference is important, because the solution is different.

Problem What's happening? Best solution
Tour Outside air enters through cracks Seal cracks, replace rubbers, adjust window
Cold drop Indoor air cools down through cold glass Install better insulating glass
Condensation Moisture settles on cold glass Ventilate and insulate glass
Cold via frame Frame is poorly insulated Improve or replace frame

Draft excluders help with cracks, but do not completely solve cold drafts through cold glass. You can read more about that difference in resolving drafts in windows.

Rule of thumb: If you feel cold air without a clear crack and the glass surface is cold, then it is a cold trap and better insulating glass helps the most.

Why does single glazing cause cold traps?

Single glazing is a poor insulator. The inside of the glass gets cold quickly in winter. Warm air from the room cools down as soon as it flows past the window. That ensures:

  • cold air flow
  • condensation
  • heat loss
  • chilly feeling
  • higher heating costs
  • less comfort

Cold drafts are often clearly noticeable with single glazing, especially with larger windows. View the options for replacing single glass.

Cold trap with old double glazing

Old double glazing insulates better than single glazing, but much less well than modern HR++ glass. As a result, the inner window can still become cold. You can often recognize old double glazing by:

  • aluminum spacer
  • no HR marking
  • production from an older period
  • noticeable cold at the window
  • condensation on the inside
  • lower insulation value
  • sometimes leakage or condensation between the glass sheets

Replacing it with HR++ glass or vacuum glass can significantly improve comfort. More about this in replace double glazing and recognize and replace leaking double glazing.

Cold trap at HR++ glass

HR++ glass greatly reduces cold draft, but does not always completely eliminate it. With large glass surfaces there can still be temperature differences, especially when it is very cold outside. Cold drop on HR++ glass can be caused by:

  • very large windows
  • poorly insulated window frames
  • cold bridges
  • ventilation grilles
  • insufficient heating
  • window to the floor
  • poor connection around the frame
  • thin curtains or no window decoration

Yet HR++ glass usually feels much more comfortable than single glazing or old double glazing. Do you want to know what exactly HR++ is? Read HR++ glass: what is it.

Cold trap with triple glazing

Triple glass insulates better than HR++ glass. As a result, the inside of the glass remains warmer and cold drafts are less noticeable. Triple glass is interesting for:

  • new construction
  • very well insulated homes
  • large windows
  • homes with low temperature heating
  • underfloor heating
  • passive house-like renovations
  • situations where comfort is important

Please note: triple glass is thicker and heavier. It does not always fit into existing window frames. Are you in doubt? Read triple glass: when to, when not to.

Cold trap with vacuum glass

Vacuum glass is thinner than triple glass, but can still insulate very well. This makes it interesting for existing window frames where triple glazing does not fit. Vacuum glass can be useful for:

  • old wooden frames
  • monumental homes
  • narrow rebates
  • existing windows with limited space
  • renovation without a thick glass structure
  • improvement in comfort while maintaining appearance

Because the inner window remains warmer, cold fall usually decreases significantly. Compare the options in vacuum glass vs HR++ glass and monument glass or vacuum glass.

Why does glass feel so cold?

Glass conducts heat better than an insulated wall. With poorly insulating glass, heat quickly escapes outside. This causes the inside of the window to become cold. The colder the glass surface, the more the air along it cools. You will especially notice this when:

  • low outside temperatures
  • large glass surfaces
  • a lot of wind on the facade
  • high humidity
  • little heating at the window
  • single glazing
  • old window frames

So the problem is not only in "air", but mainly in surface temperature. The surface temperature is related to the insulation value: see the u-value of glass. You can quickly calculate the insulation value of your glass structure with our U-value calculator.

Radiator under the window: why does that help?

In the past, radiators were often placed under windows. That was not without reason. The radiator heats the cold air that sinks past the window. This means you feel less cold. A radiator under the window ensures:

  • warm air flow upwards
  • less cold air over the floor
  • better comfort zone
  • less condensation
  • warmer window zone

In modern homes with underfloor heating, radiators are often no longer located under windows. Then good insulating glass is extra important.

Cold trap with underfloor heating

With underfloor heating the heat distribution is different than with radiators. The floor becomes warm, but there is less strong warm air flow up past the window. Cold drafts can therefore be more noticeable on large windows, especially if the glass insulates moderately. Solutions:

  • better insulating glass
  • triple glass or vacuum glass for large windows
  • good gap sealing
  • curtains or window decoration
  • convector pit or low convector with large glass area
  • well insulated window frames

The choice of glass is therefore extra important with underfloor heating and large glass areas.

Large windows and cold trap

The larger the glass surface, the greater the chance that you will feel a cold drop. A large window cools more air than a small window. Cold traps often occur with:

  • sliding doors
  • glass to the floor
  • bay windows
  • greenhouses
  • expand
  • large living room fronts
  • French doors
  • glass walls

With large windows, better glass has a great effect on comfort.

Image: large living room door down to the floor with cold air flow sinking towards the floor surface

Cold trap at sliding doors

A sliding door often has a lot of glass surface. If the glass is old or the facade closes poorly, you can experience both cold and draughts. Check for sliding doors:

  • glass structure
  • rubbers
  • brush seals
  • rails
  • closure
  • crack at sill
  • condensation
  • cold at floor

Is the glass old? Then new insulating glass can help. Does the facade close poorly? Then rubbers, rails or closure must be addressed.

Cold trap from floor-to-ceiling windows

Floor-to-ceiling windows provide a lot of light, but cold air sinks directly to the floor. This makes the area near the window quickly feel cold. Solutions:

  • HR++ or triple glazing
  • vacuum glass for existing window frames
  • good curtains
  • low convector
  • adjust underfloor heating properly
  • check cold bridges
  • improve gap sealing

For floor-to-ceiling windows, comfort glass is often more important than for small windows at parapet height.

Condensation and cold fall

Condensation and cold fall often have the same cause: cold glass. Warm moist air hits the cold glass, cools and moisture precipitates. You will then see:

  • water drops on glass
  • wet windowsill
  • mold on sealant edges
  • moisture at the bottom of the window
  • musty smell
  • black edges

Better insulating glass increases the temperature of the inner glass surface. This reduces the chance of condensation. Ventilation remains important. More about this in condensation on windows inside, outside and between glass.

Cold trap through window frames

Not only glass can cause cold. Window frames can also be cold, especially old aluminum or poorly insulated window frames. You can recognize cold through window frames by:

  • cold edge around glass
  • condensation on frame
  • mold at connection
  • cold day side
  • draft feeling along the frame
  • heat loss upon connection

Solutions can be:

  • improve window frames
  • replace rubbers
  • repair crack seal
  • installing insulating glazing
  • replace frame in case of serious problems

With good insulation, the glass and frame must be correct.

Cold trap through ventilation grilles

Sometimes cold air seems to come through glass, while cold air comes from a ventilation grille. Grilles deliberately let air in, but can feel cold in the wind. Check:

  • is the schedule open?
  • does the airflow come from above the window?
  • is the grill dirty?
  • does the valve work properly?
  • is there a lot of wind on the facade?
  • is there sufficient heating in the room?

Do not permanently close grilles without an alternative to ventilation. This can cause moisture and mold. You can read more about ventilation in glass at ventilation grille in glass; You can find a new, more adjustable version at our ventilation grilles.

Do curtains help against cold?

Curtains can help, but they do not solve the cause. They form an extra layer between window and room, so that cold air flows less directly into the room. Good curtains can ensure:

  • less cold radiation
  • less air movement
  • more comfort
  • warmer seating area
  • less heat loss

Please note: if curtains close all the way to the windowsill or floor, condensation may form behind the curtain. Ventilation remains important.

Does window film help against cold?

Insulating window film can temporarily help with single glazing. It creates an extra layer of air, which makes the glass feel slightly less cold.

Benefits Disadvantages
cheap less beautiful
quick to apply temporary
temporary comfort vulnerable
less condensation not comparable to HR++ glass
useful for rental properties can reduce vision

Window film is mainly a temporary solution, not a full-fledged replacement for insulating glass.

Does HR++ glass help against cold?

Yes, HR++ glass often helps against cold. The inside of HR++ glass remains warmer than with single glazing or old double glazing. As a result, the indoor air cools less strongly. Advantages:

  • less cold
  • less heat loss
  • less condensation
  • more comfort
  • lower energy costs
  • often fits into existing window frames

HR++ glass is a logical upgrade for many homes. You can immediately customize your HR++ window.

Does triple glazing help even better?

Triple glass insulates even better than HR++ glass. This keeps the inner window warmer and makes the cold fall even less noticeable. Triple glass is especially interesting for:

  • new construction
  • large glass areas
  • very well insulated homes
  • low temperature heating
  • homes with high comfort requirements

But triple glazing does not always fit into existing window frames. It is thicker and heavier than HR++ glass. Does it fit? Then you can customize your triple glass.

Does vacuum glass help against cold?

Vacuum glass can be a good solution if you want a lot of insulation, but have little space in the frame. It is thinner than triple glass and can still insulate strongly. Interesting at:

  • old window frames
  • monuments
  • renovations
  • homes where HR++ or triple does not fit well
  • preservation of narrow glazing beads
  • improvement of comfort

Vacuum glass can significantly reduce cold without always having to replace the entire frame. Would you like to see the glass types side by side? View compare insulating glass: HR++, triple and vacuum.

What can you do temporarily against cold weather?

Workarounds:

  • hang thick curtains
  • install window film
  • use radiator foil behind radiator
  • move furniture a little further away from windows
  • carpet in cold window area
  • Adjust ventilation grilles properly
  • check the gap seal
  • distribute heating better

This helps with comfort, but with bad glass the cause remains.

When should you replace glass?

Replacing glass is wise when cold is clearly caused by poorly insulating glass. Replacement makes sense when:

  • single glazing
  • old double glazing
  • a lot of condensation
  • cold air flow without a gap
  • high energy costs
  • large windows
  • sliding doors
  • comfort complaints
  • construction or renovation
  • poor energy label

Possible choices are HR++ glass, triple glass or vacuum glass.

When should your window frame be replaced?

Sometimes just replacing glass is not enough. If the frame is bad, the comfort problem remains. Frame replacement may be necessary for:

  • wood rot
  • warped windows
  • poor closure
  • single glazing in very old windows
  • too little space for insulating glass
  • cold aluminum frames without thermal break
  • poor connection with facade
  • many cracks

With good wooden frames, replacing glass is often sufficient. With bad window frames you have to look more broadly.

Common mistakes during cold spells

  1. Confuse a cold draft with a draft — during a cold draft, no outside air comes through a crack.
  2. Install draft excluders only — draft excluders help with cracks, but not with cold glass.
  3. Closing ventilation grilles — this can cause moisture problems.
  4. No attention to glass surface — large windows produce cold drafts more quickly.
  5. Completely close curtains without ventilation — this can cause condensation behind the curtain.
  6. Only look at glass — frames, grilles and connections also play a role.
  7. Replaced too late — single glazing or old double glazing continues to cause comfort problems.

Selection aid: what helps against cold spells?

Situation Best solution
Single glazing HR++ glass, vacuum glass or monument glass
Old double glazing HR++ glass or vacuum glass
Large glass area HR++, triple or vacuum glass
Windows to floor Better glass and possibly convector
Underfloor heating Good insulating glass is extra important
Rental property Window film and curtains as a temporary solution
Memorial Monument glass or vacuum glass
Bad window frames Repair or replace frame
Also a real trip Check rubbers, sealant and closures
Condensation on glass Insulate and ventilate

Cold trap checklist

Check these points:

  • Do you feel cold air without a clear crack?
  • Is the glass single, old double, HR++ or triple?
  • Is there condensation on the window? -Are the windows large?
  • Does the glass extend to the floor?
  • Is there a radiator under the window?
  • Do you have underfloor heating?
  • Are ventilation grilles open?
  • Do windows close properly?
  • Are window frames cold or poorly insulated?
  • Is there a real draft through cracks?
  • Are curtains available?
  • Is glass replacement possible in the existing frame?
  • Is vacuum glass interesting due to limited space?

Conclusion

Cold fall near windows often feels like a draught, but has a different cause. Warm indoor air cools along cold glass and then sinks downwards. As a result, you feel a cold air flow, especially with single glazing, old double glazing and large windows.

The best solution is usually better insulating glass. HR++ glass greatly reduces cold draft, triple glazing does this even better and vacuum glass is interesting when you have little space in existing window frames. Also check rubbers, sealant seams, window frames and ventilation grilles, because sometimes several problems occur at the same time. Temporary solutions such as curtains or window film can help, but do not completely solve the cause. If you want lasting more comfort, glass with better insulation value is often the most important step.

Further reading: resolve drafts on windows, condensation on windows, compare insulating glass and the u-value of glass.

Ready to tackle cold snap? Determine your size on custom glass, put together your custom insulating glass or contact contact for personal advice.