Why Does Your House Get So Hot Through the Windows?
Your house can feel fine in the morning.
Then the sun reaches one side of the property and suddenly the bedroom, living room or extension feels completely different.
The heating is off.
The outdoor temperature might not even seem particularly extreme.
Yet the room becomes warm enough that you start opening every window you can.
A major reason can be heat through windows.
Glass gives us daylight and views, but it also allows solar energy to enter a building. Depending on the glazing, orientation and size of the window, a room can gain a surprising amount of warmth from direct sunlight.
This is especially noticeable in properties with large areas of glazing.
Think:
- Bay windows
- Large bedroom windows
- Patio doors
- French doors
- Conservatories
- Glazed extensions
- South-facing living rooms
The Glass and Glazing Federation explains that some Low-E glazing can allow useful solar heat into a property, but in certain situations this can contribute to overheating. It recommends considering solar-control glazing for large glazed areas where excessive solar gain could become uncomfortable.
At Glass Tec Windows, we manufacture uPVC windows and double-glazed units in Bradford for homes throughout Yorkshire.
If your rooms regularly become uncomfortable because of heat through windows, the glass specification can matter just as much as the frame.
Why Can Windows Make a Room So Hot?
Sunlight contains energy.
When solar radiation passes through a window and reaches floors, walls, furniture and other surfaces inside the room, some of that energy is absorbed and converted into heat.
The room then begins warming.
Once that energy has entered the building, getting rid of it can be more difficult than preventing some of it from entering in the first place.
Pilkington explains that excessive solar heat entering through glazing can be a problem during warmer conditions and that solar-control glass can reduce the amount of solar energy transmitted through the glass.
This is why heat through windows can become particularly noticeable in rooms receiving hours of uninterrupted sunlight.
Why Can It Feel Hot When It Is Only 22°C Outside?
Outdoor air temperature does not tell you how much solar energy is reaching a particular window.
A room can therefore become uncomfortable even when the weather forecast does not look extreme.
Imagine a large west-facing bedroom window.
During the afternoon, direct sunlight reaches the glass for several hours.
Furniture, flooring and walls absorb some of that energy and gradually release it into the room.
The temperature inside can continue increasing even though the outdoor temperature itself remains relatively moderate.
That is why controlling heat through windows is about more than simply checking how many degrees the weather app shows.
Sun direction, glass area and glazing specification all matter.
South and West-Facing Windows Can Feel Completely Different
The direction a window faces can have a major effect on solar exposure.
South-facing glazing can receive substantial sunlight across the day.
West-facing glazing can receive strong afternoon and evening sun at the exact time a property may already have warmed up.
That can make bedrooms particularly uncomfortable before bedtime.
Pilkington specifically identifies south-facing glazing, glazed extensions and large areas of glass as applications where solar-control products can be useful.
This helps explain why one room can struggle with heat through windows while another room on the opposite side of the same property stays comfortable.
The windows may even be the same size.
Their solar exposure is not.
Larger Windows Mean More Solar Exposure
Large glazing has become incredibly popular in modern homes.
Homeowners want more natural light, larger views and a stronger connection between indoor and outdoor spaces.
And visually, large windows can look brilliant.
But there is a trade-off.
Increasing the glazed area also increases the area through which solar energy can enter.
A small bathroom window and a three-metre-wide glazed opening are clearly not going to behave identically.
That does not make large glazing bad.
It simply makes the glass specification more important.
If heat through windows is already a problem in a large living room or extension, replacing the glazing with another unit should involve more thought than simply asking for “double glazing.”
Double Glazing Does Not Automatically Stop Solar Heat
This is a common misunderstanding.
Double glazing is often associated with keeping a home warm.
That is true in the sense that modern insulating glass units are designed to reduce heat transfer from inside the property towards colder outdoor conditions.
But keeping heat inside during winter and controlling solar energy entering during summer are not exactly the same job.
A double-glazed unit can provide strong insulation while still allowing a useful amount of solar energy into the room.
The GGF explains that certain Low-E glass is specifically designed to admit short-wave solar energy while reflecting long-wave heat from inside the room back into the property.
That can be beneficial during colder weather.
During strong summer sunshine, however, excessive heat through windows may become less welcome.
This Is Where Solar-Control Glass Comes In
Solar-control glass is designed to reduce excessive solar heat gain through glazing.
It can achieve this in several ways depending on the product.
Some products use tinted glass.
Others use specialist coatings.
Pilkington’s solar-control range includes coated products designed to reduce solar heat while maintaining useful levels of daylight.
This makes solar-control glazing particularly interesting for:
- Large windows
- Glazed extensions
- Conservatories
- Patio and bi-fold door areas
- Strongly sun-exposed elevations
If excessive heat through windows is already making a room uncomfortable, discussing solar performance before ordering replacement glazing can be worthwhile.
Read Pilkington’s solar-control glazing guidance
What Is a Glass G-Value?
People shopping for energy-efficient windows often hear about U-values.
Far fewer hear about g-values.
They measure different things.
A U-value relates to heat transfer through a building component.
A glazing g-value relates to how much solar energy passes through the glass and ultimately enters the building.
Generally, a lower g-value means less solar heat gain through the glazing.
Pilkington describes the g-value as an important measure when specifying solar-control products because it represents the total amount of solar radiation entering through the glass.
So if excessive heat through windows is your main concern, simply asking which glass has the lowest U-value does not tell the entire story.
Both winter insulation and summer solar gain may need consideration.
Low-E Glass and Solar-Control Glass Are Not Exactly the Same
Low-E glass is primarily associated with reducing heat loss from inside the home.
A microscopic coating helps reflect long-wave heat back towards the room.
Solar-control glazing is designed to reduce excessive solar heat entering from outside.
Some modern products can combine both properties.
Pilkington’s Suncool range, for example, combines solar-control and low-emissivity performance.
That means glazing can potentially help reduce unwanted heat through windows during sunny periods while still providing useful thermal insulation during colder weather.
The correct specification depends on the particular room and property.
Will Solar-Control Glass Make the Room Dark?
Not necessarily.
Reducing solar heat does not automatically mean turning your window into dark sunglasses.
Modern solar-control products are available with different levels of light transmission, solar control and appearance.
Pilkington notes that coated solar-control glass can reduce solar gain while still allowing high levels of natural daylight into a building.
Some products are relatively neutral in appearance.
Others can intentionally have a tint or stronger reflective appearance.
This is why homeowners should compare both performance and aesthetics.
The goal is not simply blocking everything coming through the window.
It is achieving an appropriate balance between daylight and heat through windows.
Why Is My Bedroom Worse Than My Living Room?
Bedrooms can be particularly affected by solar gain because of timing.
Imagine a west-facing bedroom.
The room receives strong sunlight during the afternoon.
The walls, floor and furniture gradually warm.
Even after the sun begins dropping, those surfaces can continue releasing heat into the room.
Then you go to bed.
The outdoor temperature may have started falling, but the room still feels noticeably warmer than the rest of the house.
This is one reason reducing heat through windows can improve comfort in certain bedrooms even if the property does not have an overheating problem everywhere.
Why Does Closing the Curtains Sometimes Make Things Worse?
Curtains and blinds can reduce direct sunlight reaching surfaces deeper within the room.
However, once solar energy has passed through the glass, it has already entered the building.
The space between the glazing and an internal blind or curtain can also become very warm.
External shading generally intercepts sunlight before it passes through the glazing, while solar-control glass reduces solar gain as part of the window itself.
That does not make curtains useless.
They can still be valuable for privacy, glare control and comfort.
But a severe heat through windows problem may require looking at the glazing itself rather than relying entirely on internal blinds.
Can New Windows Make Overheating Worse?
Potentially, depending on the specification and building.
Modern windows can be extremely good at reducing heat loss.
That is excellent during colder conditions.
But if a highly insulated room also receives significant solar energy through large glazing, the heat entering the room can become harder to escape.
The GGF acknowledges this issue, noting that some thermally efficient Low-E glass can contribute to overheating where solar gain is excessive.
This is not an argument against energy-efficient glazing.
It means windows should be specified for the actual property.
If you have a large south-facing opening already struggling with heat through windows, tell the supplier before choosing the replacement glass.
Does Triple Glazing Solve Overheating?
Triple glazing can alter both thermal insulation and solar performance, but simply adding another pane should not be treated as a universal overheating solution.
Pilkington notes that corresponding triple-glazed units can have lower solar gain than some double-glazed arrangements, but the actual performance depends on the glass specification.
The correct choice depends on what you are trying to achieve.
If winter heat retention is the main concern, one specification may be appropriate.
If strong summer solar gain is the bigger problem, another combination may make more sense.
Glass Tec offers both double-glazed windows and triple glazing in Bradford for homeowners comparing different glazing options.
What About Patio Doors and Large Glazed Doors?
Large glazed doors can create the same issue on an even bigger scale.
A patio door introduces far more glass into a wall than a conventional small window.
That can make the room brighter and more open.
But if those doors receive strong direct sunlight, they also create a larger route for heat through windows and glazed doors.
This is particularly relevant for rear extensions where homeowners frequently combine:
- Large doors
- Roof glazing
- Rooflights
- Large side windows
Each individual piece of glass contributes to the complete solar gain of the room.
The glazing should therefore be considered as a whole.
Conservatories Are the Obvious Example
Anyone who has entered an older conservatory on a sunny day knows how dramatic solar gain can become.
Large areas of glass receive sunlight from several directions.
Pilkington specifically recommends combining thermal insulation and solar-control properties for conservatories and highlights south- and west-facing glazing as areas where solar control may be particularly useful.
A conservatory is an extreme example, but the same principle applies to ordinary rooms.
The larger and more exposed the glazing, the more important controlling heat through windows can become.
Solar-Control Glass Can Still Be Clear
Many people imagine solar-control glass as extremely dark or mirrored.
That is not always the case.
Coated solar-control products can provide relatively neutral-looking glazing while reducing the amount of solar energy entering the building.
Pilkington Suncool products, for example, are available with different combinations of solar control, light transmission and reflection.
That means homeowners do not necessarily have to choose between a bright room and controlling excessive heat through windows.
The exact appearance and performance should still be checked before ordering.
What About Window Film?
Window films can also be used in some situations to reduce solar heat and glare.
The Glass and Glazing Federation explains that suitable window film can reduce solar heat entering through existing glazing and can improve comfort.
However, the correct product and compatibility with the existing glass matter.
A professionally specified glazing solution may be more appropriate when windows are already being replaced.
If the frames are old, draughty or otherwise due for replacement, choosing the right glass at the same time can address the complete window rather than applying a separate treatment afterwards.
Read the GGF’s window-film guidance
Do Open Windows Fix the Problem?
Opening a window can help remove heat when outdoor conditions allow it.
But ventilation does not stop the solar energy entering through the glass in the first place.
Pilkington notes that solar-control glass does not work entirely in isolation and that adequate ventilation remains important for preventing accumulated heat from becoming uncomfortable.
The two approaches perform different jobs.
Solar control helps reduce heat entering.
Ventilation helps remove heat that is already inside.
A room experiencing strong heat through windows may benefit from considering both.
Why Glass Specification Matters Before Manufacturing
Once a sealed double-glazed unit has been manufactured, its glass combination has already been decided.
That means questions about solar performance are best raised before the windows are ordered.
A homeowner might spend a lot of time choosing:
- Frame colour
- Handle colour
- Opening style
- Georgian bars
- Glass pattern
while barely discussing the thermal and solar properties of the actual glazing.
For a heavily sun-exposed room, that is backwards.
The glass occupies most of the visible window area.
Its specification can have a significant influence on both winter and summer comfort.
Glass Tec manufactures sealed glazing units and uPVC windows in Bradford, allowing the glass and frame specification to be considered together.
Can Solar-Control Glass Reduce Glare Too?
Depending on the product, solar-control glazing can also reduce excessive glare.
Bright sunlight reflected from televisions, monitors and glossy surfaces can make a sunny room uncomfortable even before temperature becomes the main issue.
Pilkington identifies glare reduction as one of the potential benefits of certain solar-control glass products.
This can be useful for living rooms, home offices and large glazed areas receiving direct sun.
Again, different products achieve different levels of solar control and visible-light transmission.
The glazing should be selected for the actual room rather than assuming every solar-control product behaves identically.
Is Solar-Control Glass Only for New Builds?
No.
Solar-control glazing is also relevant to replacement and retrofit projects.
Pilkington lists replacement windows and solar-control upgrades to existing homes among the applications for its Suncool range.
That means homeowners dealing with excessive heat through windows do not necessarily need a completely new house or extension to consider solar performance.
If the existing windows are already due for replacement, it can be an ideal time to discuss the problem.
New-Build Regulations Also Recognise Overheating
Overheating has become important enough to receive its own section of the Building Regulations for new residential buildings in England.
Approved Document O addresses overheating risk in new homes and includes measures relating to glazing, solar gain and shading.
The Government confirms that Part O applies to new residential buildings and includes standards intended to limit solar gains.
That does not mean every existing homeowner needs to apply Part O when replacing a window.
It does show how seriously overheating from solar gain is now considered in building design.
Read the Government’s Approved Document O guidance
When Should You Consider Different Glazing?
It may be worth discussing solar performance if:
- One room regularly becomes excessively hot in direct sunlight
- You have very large windows
- The glazing faces south or west
- A conservatory becomes unusable during sunny weather
- Large patio or bi-fold doors receive direct afternoon sun
- You are replacing glazing in an already hot extension
- You want to reduce solar gain while keeping natural daylight
These symptoms do not automatically mean every pane needs specialist solar-control glass.
But they do give your window supplier useful information.
The biggest mistake is ordering exactly the same glazing specification without mentioning that heat through windows is already one of the main reasons you are replacing them.
Why Replacement Windows Can Be an Opportunity
Replacing windows is not only about removing old frames.
It is an opportunity to reconsider how the room actually performs.
Perhaps the existing windows:
- Lose too much heat during winter
- Allow excessive solar gain in summer
- Let in unwanted draughts
- Have failed sealed units
- No longer close correctly
- Lack the glass performance you want
Modern glazing offers far more specification choices than simply “single or double glazed.”
Depending on the project, the glass can be selected for thermal performance, solar control, safety, security, noise reduction and appearance.
If heat through windows is one of the main problems in your home, it deserves to be part of that conversation from the beginning.
Frequently Asked Questions
Why Does So Much Heat Come Through My Windows?
Sunlight carries solar energy through the glazing.
When indoor surfaces absorb that energy, the room warms.
Large and strongly sun-exposed glazing can make heat through windows particularly noticeable.
Does Double Glazing Stop Heat From the Sun?
Double glazing primarily provides insulation between indoor and outdoor conditions.
The amount of solar energy entering depends on the actual glass specification.
Solar-control glazing can be used where excessive solar gain needs to be reduced.
What Is Solar-Control Glass?
Solar-control glass is designed to reduce the amount of solar heat transmitted into a building while still allowing useful daylight.
Products can use specialist coatings, tinted glass or combinations of technologies.
Will Solar-Control Glass Make My Windows Dark?
Not necessarily.
Modern products are available with different levels of visible-light transmission, reflection and solar-control performance.
Some can maintain a relatively neutral appearance.
Why Is My West-Facing Bedroom So Hot?
West-facing windows can receive strong afternoon and evening sunlight.
That solar energy can continue warming the room shortly before bedtime, making heat through windows especially noticeable.
Is Triple Glazing Better for Keeping Summer Heat Out?
Triple glazing can have different solar performance from double glazing, but the glass specification matters.
The number of panes alone does not tell you how much solar energy the finished window will admit.
Can I Get Solar-Control Glass in Replacement Windows?
Yes.
Solar-control products can be suitable for replacement and retrofit windows depending on the application and required specification.
Can Better Windows Keep My House Cooler and Warmer?
A properly selected glazing system can combine thermal insulation with solar-control properties.
That can help retain indoor warmth during colder periods while reducing excessive solar gain when the sun is strong.
Is Too Much Heat Coming Through Your Windows?
A bright room is brilliant.
A room that becomes uncomfortable every time the sun appears is not.
If heat through windows is making a bedroom, living room, conservatory or extension difficult to use, the glass specification deserves attention.
Solar-control glazing can reduce excessive solar gain while modern Low-E technology can help retain warmth during colder conditions.
The right balance depends on the window position, amount of glazing and way the room is used.
Glass Tec Windows manufactures double-glazed units and uPVC windows in Bradford and supplies and installs windows across Bradford, Leeds, Halifax, Huddersfield, Wakefield and wider Yorkshire.
Explore our double-glazed windows or contact Glass Tec Windows to discuss glazing for a room affected by excessive solar heat.
