Key Takeaways
- Yes, double glazing helps keep heat out in summer, because the sealed gap between the panes slows heat moving through the window.
- Double glazing typically reduces heat loss or gain by 75% to 80% compared with single glazing.
- Low-E coatings, argon gas and warm edge spacers add to the effect by reflecting heat and limiting transfer across the gap.
- For the best summer results, combine double glazing with external shading, sensible window placement and good ventilation at night.
Does Double Glazing Keep Heat Out in Summer?
It does. A double glazed window has two panes of glass separated by a sealed space, and that space acts as a barrier to heat. In summer, the outer pane warms up in the sun, but much less of that heat crosses the gap to the inner pane.
The same design that traps warmth in winter slows heat from entering in summer. That is why double glazing is described as an all-year upgrade, not only a winter fix.
- Insulating gap: a sealed 16mm space filled with argon gas slows conduction.
- Low-E coating: reflects part of the sun’s heat energy before it enters the room.
- Warm edge spacers: non-metal spacers limit heat moving through the glass edge.
- Insulating frames: uPVC does not heat up and conduct the way bare metal does.
How Heat Gets Into a Room Through a Window
Heat enters through windows in three ways, and glazing affects each differently. Knowing which one you are fighting helps you choose the right fix.
| Heat path | What happens | What helps most |
|---|---|---|
| Radiation | Sunlight passes through the glass and warms the room | Low-E or tinted glass, external shading |
| Conduction | Heat moves through glass and frame materials | Double glazing, insulating uPVC frames |
| Air leakage | Hot air enters through gaps around the sash | Compression seals, careful installation |
Double glazing helps with conduction and, with Low-E coatings, with radiation. Air leakage is solved by seals and fitting, which is why installation quality matters.
Do Double Glazed Windows Keep Heat Out Better Than Single Glazing?
Yes, by a large margin. Single glazing has one thin pane, so heat passes through quickly. Double glazing typically reduces heat loss or gain by 75% to 80% compared with single glazing.
The inside pane also stays closer to room temperature. That means you feel less radiant heat from the glass itself on a hot afternoon.
- Single glazing: the inner glass heats up quickly in direct sun.
- Double glazing: the sealed gap slows heat so the inner pane stays cooler.
- Double glazing with Low-E: reflects more of the sun’s energy on the way in.
Our guide on how double glazing works in every season covers the winter side of the same story.
Glass Features That Matter Most in Summer
Not all double glazing performs the same. The glass specification decides how much summer heat you block.
- Low-E coating: a thin layer that reflects heat, typically adding 10 to 20% to the price of a window.
- Argon gas: denser than air, so it slows heat transfer; it is standard in our double glazed units at no extra cost.
- Tinted glass: reduces glare and absorbs some solar energy, at the expense of some natural light.
- Triple glazing: adds a second gap for even greater insulation where it is needed.
To compare coatings in detail, read about Low-E glass for summer heat. If you are weighing another pane, see triple glazing for extra heat control.
Why Your Room Might Still Feel Hot
Double glazing is not a cure-all. If a room still overheats, one of these common factors is usually responsible.
- Large west-facing glass: afternoon sun delivers intense heat that glazing alone cannot fully block.
- No shading: eaves, awnings or external blinds stop the sun before it reaches the glass.
- Trapped hot air: a closed house can hold the heat that built up during the day.
- Poor installation: gaps around the frame let hot air leak in.
- Dark, heat-absorbing surfaces: roofs, walls and furniture re-radiate heat indoors.
How to Keep Your Home Cooler With Double Glazing
Pair your windows with simple habits. These steps get the most from your glazing on hot days.
- Close external blinds or shutters on sun-facing windows during the hottest part of the day.
- Choose Low-E glass for west and north-facing windows.
- Add eaves, pergolas or shade sails to block the high summer sun.
- Open windows at night and early morning to flush out heat when it is cooler outside.
- Keep doors and windows closed in the heat of the day, so hot air stays out.
- Choose operable windows with good seals, so ventilation is controllable.
Frames, Seals and Installation Also Count
Glass gets most of the attention, yet the rest of the window decides whether the glass can do its job. A great pane in a leaky or conductive frame loses much of its benefit.
- Frame material: uPVC is a natural insulator, so the frame stays cooler than bare metal in direct sun.
- Compression seals: tight gaskets stop hot air entering around the sash.
- Multi-point locking: pulls the sash evenly against the seals.
- Accurate fitting: a made-to-measure window sealed to the wall avoids gaps.
The Ultimate Windows Difference
Our uPVC windows are up to 4.5 times more energy efficient than standard aluminium-framed windows. We make them at our solar powered factory in Wodonga, Victoria, from Deceuninck European-designed profiles.
Ultimate Windows says double glazing can slash your annual power bill by up to 90%. One customer reported: “They have reduced our power bills & north facing, we have significantly noticed the difference both in summer & winter, including noise reduction.”
- Argon as standard: no extra cost for the gas fill.
- Compression seals: help block hot air leaking around the sash.
- In-house installers: the same team fits every window.
- 12-year guarantee: seven years longer than the five years the AWA recommends.
Frequently Asked Questions
Does double glazing keep heat out in summer?
Yes. The sealed gap between two panes slows heat moving through the window, and Low-E coatings and argon gas improve this further. Double glazing typically reduces heat gain by 75% to 80% compared with single glazing, though shading and ventilation help too.
Why is my room still hot with double glazing?
Large west-facing windows, lack of external shading, trapped hot air or gaps around the frame can all let heat build up. Double glazing reduces heat transfer but cannot block all of it. Adding shading, Low-E glass and night ventilation usually solves the problem.
Is Low-E glass better than tinted glass for summer heat?
Low-E reflects heat while keeping views clear and letting natural light through, so it suits most homes. Tinted glass absorbs more solar energy and reduces glare but also darkens the room. The best choice depends on the orientation and how much light you want.
Which windows need the most heat protection?
West-facing windows take the strongest afternoon sun in summer, so they usually need the most protection. North-facing windows also gain heat but are easier to shade with eaves. Prioritise Low-E double glazing and external shading on west walls first, then work around the house.
Keep Summer Heat Out With Ultimate Windows
If hot rooms are costing you comfort and energy, our team can recommend the right glass and window styles. Book a free measure and fixed-price quote, or call 1300 898 782 to get started.
