Does Window Film Really Reduce Heat in a Home or Business?

If you have one room in your house that is noticeably hotter than the others—or a desk, waiting area or storefront that becomes uncomfortable every afternoon—the windows may be a big part of the problem.

Sunlight passing through glass does more than brighten a room. It also carries solar energy into the space. Floors, furniture, counters and other surfaces absorb that energy and warm up, which can leave the room uncomfortable even while the air conditioner is running.

Architectural window film can reduce the amount of solar energy entering through the glass. It will not fix every reason a building gets hot, but when the windows are a major source of heat gain, the difference can be meaningful.

Questions answered in this article

• How does architectural window film reduce heat?
• Will window film actually make a room cooler?
• Can window film help reduce air-conditioning use?
• Will heat-control window film make the room dark?
• Is reflective or ceramic window film better for heat?
• Which FlexFilm architectural film is best for heat reduction?
• Why might a room still be hot after window film is installed?
• Can window film be installed on any type of glass?
• Does architectural film work for businesses as well as homes?

How does architectural window film reduce heat?

When sunlight reaches a window, solar energy can pass through the glass, reflect away from it or be absorbed by the glass and film.

Architectural window films are designed to change that balance.

Some films rely heavily on reflection. They send more solar energy back toward the exterior before it can enter the room.

Other films, including ceramic products, rely more heavily on absorption while maintaining a less reflective appearance.

The important point is that visible darkness and heat performance are not the same thing.

A film does not necessarily need to make the windows very dark to improve solar control. The materials inside the film and the way they interact with solar energy matter just as much as the shade you see.

For buildings, one useful performance measurement is Solar Heat Gain Coefficient, or SHGC. It describes how much solar heat is admitted through the complete window system. A lower SHGC indicates that less solar heat is passing into the building.

The exact performance of a filmed window depends on both the film and the glass underneath it.

Will window film actually make a room cooler?

It can make a room more comfortable when solar heat through the windows is contributing to the problem.

What we would not do is promise that every room will become a certain number of degrees cooler.

There are too many variables for that to be honest.

The result depends on things such as:

• Which direction the windows face
• How many hours of direct sunlight they receive
• The size and number of windows
• The type of glass
• The film selected
• Exterior shade from trees, rooflines or nearby buildings
• Interior blinds or curtains
• Ceiling height
• Insulation
• Air-conditioning performance
• Heat coming through the roof or walls
• Equipment, lighting and people inside a commercial space

A west-facing room that becomes uncomfortable every afternoon because sunlight pours through a large wall of glass may respond very well to solar-control film.

A room that stays hot all night because of poor insulation or an undersized air conditioner has a different problem. Window film may still help during the day, but it cannot correct issues that have nothing to do with the glass.

This is why we prefer to understand what is making the space uncomfortable before recommending a film.

Can window film help reduce air-conditioning use?

Potentially, yes.

When less solar heat enters through the windows, the cooling system has less incoming heat to remove from the building.

That can be especially useful in spaces with large areas of sun-exposed glass, such as:

• Living rooms with oversized windows
• Offices with exterior glass walls
• Storefronts
• Waiting rooms
• Restaurants
• Conference rooms
• South- or west-facing rooms
• Upper-floor spaces with strong afternoon sun

Window film does not make the air conditioner more powerful. It reduces one source of heat entering the space.

We would not promise a specific percentage reduction in an electric bill without an energy analysis of the building. Energy use depends on the HVAC system, insulation, thermostat settings, climate, occupancy and many other factors besides the windows.

The more useful expectation is that reducing solar heat gain can lessen the cooling load associated with sun-exposed glass.

Will heat-control window film make the room dark?

Not necessarily.

Architectural film comes in very different appearances.

Some reflective solar-control films noticeably change the exterior appearance of the glass and reduce more visible light. Other products are designed to maintain a more natural view.

FlexFilm's architectural lineup includes reflective, dual-reflective, sputtered and ceramic solar-control options. There is no single appearance that applies to all architectural tint.

A customer who wants strong daytime privacy may intentionally choose a more reflective product.

Someone who loves the natural appearance of their windows and mainly wants help with heat may prefer a lower-reflectivity option.

This is one reason we do not recommend choosing architectural film based only on the darkest sample.

The first question should be: What problem are you trying to solve?

Then we can consider how much change in appearance you are comfortable with.

Is reflective or ceramic window film better for heat?

Neither technology is automatically the best choice for every window.

Reflective films are designed to send a larger portion of solar energy away from the glass. That can provide strong solar control and is one reason reflective architectural films are common on commercial buildings and sun-exposed homes.

Ceramic architectural film works differently. It relies more heavily on absorbing solar energy and can provide heat control with a much less reflective appearance.

That difference affects more than appearance.

Because an absorptive film causes the glass to retain more heat, the glass construction has to be evaluated carefully. The wrong film on the wrong window can increase thermal stress.

Reflective film also needs to be selected appropriately for the glass and installation conditions.

The choice therefore depends on several things:

• Glass construction
• Single-pane or double-pane glass
• Whether a Low-E coating is present
• Window size
• Existing damage
• Sun exposure
• Exterior shading
• Desired appearance
• Privacy needs
• Glare
• Heat-control goals

A film that performs well on one building is not automatically the correct choice for another.

Which FlexFilm architectural film is best for heat reduction?

FlexFilm offers several architectural technologies rather than one universal heat-control film.

Dualflex Dual Reflective is designed for strong solar control with a reflective exterior and a more natural view from inside. It can be a useful choice when heat and glare are priorities but the customer does not want the interior to feel heavily mirrored.

Chromoflex Silver Reflective provides a more pronounced reflective appearance. It is intended for strong solar control and daytime privacy, making it useful for certain storefronts, offices and buildings where the mirrored appearance is acceptable or desired.

Panashield Architectural Ceramic is the low-reflectivity option. FlexFilm advertises Panashield at up to 89% rejection of broad-spectrum infrared radiation. It is designed for customers who want heat control while preserving a more natural-looking window.

That 89% figure refers to FlexFilm's infrared measurement. It should not be interpreted as meaning the film blocks 89% of all solar heat.

Depending on the project, FlexFilm also offers other architectural solar-control technologies.

We do not choose between these products based only on which one has the largest number on a specification sheet. The glass has to be compatible with the film, and the customer's goals for heat, glare, privacy and appearance all matter.

Why might a room still be hot after window film is installed?

Window film addresses heat entering through the glass. A building can gain heat from many other places.

A room may still be warmer than expected because of:

• Poor attic or wall insulation
• Direct sun on the roof
• Air leaks
• An undersized or poorly functioning HVAC system
• Unbalanced ductwork
• Large amounts of heat-producing equipment
• High ceilings
• Frequently opened exterior doors
• Untreated skylights or other windows
• Heat coming through adjacent rooms

There is also an important difference between reducing heat gain and making a room cold.

If sunlight is pouring through a window, properly selected film can reduce that solar load. The room will still be affected by the outdoor temperature and every other source of heat in the building.

We prefer to describe window film as a solar-control tool rather than a cure for every comfort problem.

Can window film be installed on any type of glass?

No.

This is one of the biggest differences between automotive and architectural window tinting.

Film selection for a home or commercial building needs to account for the actual glass construction.

Important factors can include:

• Single-pane or double-pane construction
• Tempered, laminated or annealed glass
• Low-E coatings
• Gas-filled insulated glass
• Glass thickness
• Window size
• Chips, scratches or damaged edges
• Window orientation
• Exterior shadows
• Nearby reflective surfaces
• Interior blinds or shades located very close to the glass

Window film changes how solar energy is absorbed, reflected and transmitted by the window. If a film causes too much heat to build up in a glass assembly that cannot safely handle it, thermal stress can increase the risk of glass damage.

For that reason, Summit Tint Studio does not treat architectural film as a one-film-fits-every-window product.

The glass should be identified and the proposed film checked for compatibility before installation.

We will cover double-pane and Low-E glass in greater detail in a separate Resource article.

Does architectural film work for businesses as well as homes?

Yes. The same basic solar-control principle applies to residential and commercial glass.

The problem being solved may be different.

At home, someone may be trying to make a living room more comfortable, protect a hardwood floor or reduce the afternoon sun on a couch.

A business may be dealing with:

• Employees sitting beside hot windows
• Computer-screen glare
• Customers uncomfortable near storefront glass
• Uneven temperatures between offices
• Merchandise exposed to sunlight
• Daytime privacy
• A large cooling load from exterior glass

Architectural film allows the solution to be tailored to the building rather than replacing perfectly usable glass simply because the room gets too much sun.

The right product still depends on the window itself.

If you are considering architectural window film for your home, office or storefront, Summit Tint Studio can evaluate the glass, measurements, sun exposure and what you want the film to accomplish before recommending an option.

Learn more about our residential window tinting and commercial window tinting services, or request an architectural quote.