Does Double Glazing Reduce Heat?

If you are wondering “does double glazing reduce heat?”, the short answer is yes. Double glazed windows can significantly reduce unwanted heat transfer through glass, which improves energy efficiency, keeps rooms more comfortable and can lower your heating and cooling costs over time. The exact result depends on how double glazing is specified, how it is installed and how it is combined with shading, frames and the rest of your home. At Trade Heroes, we connect Australian homeowners with experienced window and glazing specialists who understand how double glazing works in real homes, not just in brochures. Below, we break down the essentials so you can choose the right double glazed windows for better heat control and indoor comfort.

How Double Glazing Works

Double glazing reduces heat by changing the way heat can move through your glazed window, using two glass panes and a sealed gap as a thermal barrier.

What Double Glazing Is

A double glazed window consists of two panes of glass separated by a spacer and sealed around the edges to form an insulated glass unit. Instead of one single pane glass window between your home and the outside air, you now have:

• An outer pane that faces the weather
• An inner pane that faces your room
• A sealed cavity between the panes that is filled with air or inert gas, often argon gas

This “glass separated by a gap” design is what makes double glazing an energy efficient window. The extra layer and cavity limit heat transfer and can also improve sound insulation, so you get a more comfortable living space with all the benefits of better thermal performance and less noise pollution.

The Air Or Gas Gap And Thermal Barrier

The sealed gap in double glazing introduces a poor heat conductor between the two panes of glass. That gap is typically filled with still air or an inert gas such as argon, which slows down:

• Heat conduction from the warm side to the cold side
• Convection currents within the cavity
• Some radiant heat transfer between the glass panes

This air or gas layer acts as a thermal barrier. In winter, it helps keep warm air inside and reduces heat loss through the glass. In summer, it helps keep external heat out so your cooling systems do not have to work as hard. Compared to single glazed windows, double glazing can reduce heat loss or heat gain through glass by around 30 percent, especially when combined with low emissivity glass, good window frames and proper installation. That is why double glazing is widely used in energy efficient homes across cold climates, mixed climates and increasingly hot Australian regions.

Double Glazing And Heat Loss In Winter

Double glazing is particularly effective at reducing heat loss in winter by slowing every pathway that heat uses to escape through a window.

How Double Glazing Slows Heat Escaping

On a cold night, single glazed windows allow heat to flow quickly from the warm interior to the cold exterior. The inside surface of the glass becomes very cold, which increases radiant heat loss from your body and makes the whole room feel chilly even when the heater is running. With double glazed windows, heat transfer is limited in three ways:

• The two panes of glass add resistance to heat conduction
• The sealed air or argon gap reduces convection and limits heat flow
• If you choose low e glass, part of the radiant heat is reflected back into the room

The result is a higher inside surface temperature on the inner pane, less heat loss and fewer cold draughts around your windows. This leads to more stable indoor temperature, reduced reliance on heating systems and the potential for lower energy bills.

U Values And Thermal Performance

Window performance is usually described using a U value. The U value tells you how easily heat passes through the whole window, including glass and frame. A lower U value means better insulation and less heat transfer. In general terms:

• Single glazed aluminium windows often have high U values and poor insulation
• Standard double glazing with air filled cavities performs better
• Double glazing with argon gas, warm edge spacers and low e coating offers excellent thermal performance
• Triple glazing can go lower again for extreme cold climates

When you are selecting double glazed windows, ask your supplier for the U value and the solar heat gain properties for each product, not just the glass, so you can compare options for maximum insulation and energy savings.

Comparing Single, Double And Triple Glazing

Here is how the main glazing types compare for winter heat loss:

• Single glazing - has one pane of glass and no insulating gap, so there is significant heat loss and little thermal barrier.
• Standard double glazing - uses two panes of glass separated by air or argon gas and can reduce heat loss or heat gain by almost 30 percent in comparison to single glazed windows.
• Triple glazing - uses three panes and two gas gaps, which improves insulation even further and is often chosen in very cold climates where heating costs can be extreme.

For most Australian homes, high performing double glazing with the right frame and low e coating offers the best balance of cost, thermal efficiency and comfort.

Double Glazing And Heat Gain In Summer

Double glazing can also help with summer comfort by reducing external heat entering your home, but you need to understand solar heat gain so you choose the right configuration.

When Double Glazing Helps Keep Heat Out

In hot weather, double glazing helps keep cool air inside and hot external air out. The insulating gap slows heat conduction and reduces the temperature difference you feel near the window. This gives your cooling systems an easier job and can reduce cooling costs when combined with good insulation and shading. Homeowners often report that after installing the right double glazed windows, the house feels cooler and less stuffy on summer afternoons, with fewer temperature fluctuations and more comfortable indoor temperatures.

The Solar Heat Gain Challenge

Solar heat gain occurs when the sun’s energy passes through the glass and heats up internal surfaces. Standard clear double glazing still allows a lot of solar heat through. On large east facing windows or west facing windows without shading, this solar heat can build up quickly. If solar gain is not controlled, the combination of high performance insulation and standard double glazing can sometimes make a house warmer than expected in summer because the heat that enters has trouble escaping again. This is why solar control and shading are as important as the glazing itself when you want to reduce heat.

Why The Wrong Glass Can Trap Unwanted Heat

If you install double glazing with clear glass everywhere and do not add shading, you can end up with:

• Overheating in rooms with large unshaded east and west facing windows
• Elevated indoor temperatures in hot weather, even with double glazing
• A greenhouse type effect where solar heat is captured but not easily released

In these situations, double glazing helps with winter heat loss but may not solve summer overheating. The solution is not to avoid double glazing, but to choose the right double glazed windows, combine them with low e or toned glass where needed and manage solar heat gain with eaves, external blinds or other shading.

The Role Of Low E Glass

Low emissivity glass is often the missing piece when homeowners want double glazing that reduces both heat loss in winter and heat gain in summer.

What Low E Coatings Do

Low e glass has a very thin, almost invisible metallic coating applied to one of the glass surfaces inside the double glazed unit. This low e coating:

• Reflects radiant heat back into the room in winter
• Reduces solar heat gain in summer on some glass types
• Allows visible light and natural light to pass through so rooms still feel bright

Used correctly, low e glass improves energy efficiency and indoor comfort by limiting heat transfer without turning your windows into dark tinted panels.

Passive Low E Vs Solar Control Low E

There are two broad categories of low e double glazing that affect how much heat is reduced:

• Passive low e double glazing - allows relatively high solar gain as well as good insulation. It is suitable for homes in colder climates or for north facing windows where winter sun is useful, and external shading or eaves can handle summer sun.
• Solar control low e double glazing - reflects more solar heat away while still letting in natural daylight. It is ideal for large east facing windows, west facing windows and other glazed areas that receive intense sun and risk overheating.

Different low e products have different performance levels, so selecting double glazed windows with the correct type of low e glass for each orientation is critical.

Combining Low E Glass With Double Glazing For Heat Control

When you combine low e glass with double glazing and argon gas, you get:

• A strong thermal barrier that reduces heat conduction and convection
• Better control of radiant heat, with more warmth kept inside in winter and less solar heat gain in summer
• The ability to fine tune performance for each part of the home by mixing passive low e and solar control low e where they suit best

This is why high performing low e double glazing is now commonly recommended for new homes aiming for good star ratings and lower energy consumption.

Other Factors That Affect How Much Heat Double Glazing Blocks

Even the best double glazed window will not perform at its full potential if other design factors are working against it.

Window Orientation And Climate

How well double glazing reduces heat depends heavily on your local climate and which way your windows face. For example:

• In cold climates, south and west facing windows often benefit most from improved insulation and lower U values to reduce winter heat loss.
• In hot and dry regions, keeping solar heat off east facing windows and west facing windows is critical, so solar control low e and shading make a big difference.
• In milder zones, a balanced approach that considers winter heating costs and summer cooling costs is usually best.

Looking at your orientation, sun path and prevailing winds helps you choose the right combination of double glazing, shading and ventilation for a comfortable indoor temperature.

Shading, Eaves And External Screens

Shading works together with double glazing to reduce solar heat. Good design might include:

• Eaves sized to block high summer sun on north facing windows while allowing winter sun
• External blinds or screens for large glazed areas that cop afternoon sun
• Pergolas, awnings or external shutters to keep external heat off the glass

When you keep direct sun off the glass for the hottest parts of the day, the double glazed units can focus on reducing general heat transfer rather than fighting direct solar heat gain.

Curtains, Blinds And Window Films

Internal window furnishings also affect how much heat enters or leaves through glazing. Heavy, lined curtains with pelmets, quality blinds and timber shutters can:

• Add another layer of insulation in winter
• Help reduce radiant heat from warm glass in summer
• Limit drafts around the edges of window frames

Glazing films and toned glass can also reduce solar heat gain on existing windows. While they are not a full substitute for double glazing, they can complement it or act as a step toward a future upgrade.

Double Glazing For Existing Homes

If you already have single glazed windows and want to reduce heat transfer, you have more than one option. Trade Heroes connects you with specialists who can explain which approach suits your house and budget.

Retrofit Double Glazing

Retrofit double glazing involves replacing the existing glass with double glazed units, often reusing the frame if it is suitable, or installing new energy efficient windows completely. This can deliver:

• Significant reductions in heat loss in winter
• Less external heat entering in summer
• Better sound insulation and less noise pollution
• A more stable indoor temperature and improved indoor comfort

When retrofit double glazing is combined with appropriate low e glass and good frames, the improvement in thermal efficiency compared to old single glazed aluminium frames is often very noticeable.

Secondary Glazing For Single Glazed Windows

Secondary glazing adds a second layer of glass or acrylic to the inside of an existing single glazed window. This creates an air gap between the old glass and the new layer, which can mimic some of the benefits of double glazing. Secondary glazing:

• Can be a cost effective option for heritage homes where replacing windows is difficult
• Reduces heat transfer and can cut heating costs
• Improves sound insulation and reduces external noise

While not identical to full double glazing, it is an effective solution for many existing windows where you want better performance without complete replacement.

When Does Double Glazing Meaningfully Reduce Heat?

Double glazing will reduce heat transfer in almost any situation, but there are specific scenarios where you will notice the biggest difference.

Situations Where You Will Notice The Biggest Difference

Double glazing is most effective at reducing heat and improving energy efficiency when:

• You are upgrading from older single glazed windows with aluminium frames
• Your home has large areas of glass that currently feel very hot in summer or very cold in winter
• You live in a climate with hot weather, cold winters or both
• You combine double glazing with good insulation, draft sealing and sensible shading

In these conditions, homeowners often report needing the heater and air conditioner less, feeling fewer cold spots and enjoying a more consistent indoor temperature, which all contribute to lower energy costs and a more comfortable living space.

When Other Upgrades May Be More Effective

There are also times when other changes may deliver better value before or alongside double glazing, such as:

• Adding ceiling or wall insulation if your roof space is poorly insulated
• Sealing obvious drafts around doors, vents and old window frames
• Installing external shading on a few problem windows that receive intense solar heat gain

In these cases, a staged approach makes sense. You can address the worst heat transfer or solar heat first, then plan for double glazing as part of a broader upgrade. If you are unsure whether double glazing will reduce heat enough in your specific home to justify the investment, the best next step is to get tailored advice rather than a one size fits all answer.

Find a Local Glazier

Double glazing reduces heat by using two panes of glass and an insulating gap to limit heat transfer through conduction, convection and radiation. When combined with low-e glass, quality frames, effective shading and good design, double glazed windows can improve energy efficiency, reduce heating and cooling costs, cut solar heat gain and create a more comfortable indoor environment in both winter and summer. If you’re exploring how double glazing could work in your home, Trade Heroes makes it easy to compare local glazing specialists, ask the right questions and request quotes for double glazed windows, glass types and installation options suited to your climate and window layout. Speaking with an experienced glazier can help identify where double glazing will deliver the biggest gains and how it can be integrated into a smarter, more energy-efficient home upgrade. You can find glaziers through Trade Heroes in Perth, Sydney, Adelaide, Melbourne, Hobart or Brisbane.