Short answer
Window film can lower the cooling part of your energy bill, because it cuts the solar heat coming through sun-facing glass before it heats the room. How much depends on your house: how much glass faces east, west and south, the glass you have now, shading, insulation, your A/C and your electricity rate. Nobody can promise a number without measuring. You can judge it yourself by comparing the same months before and after, the temperature in the sunny rooms, and how long your A/C runs.
How windows heat a house
Sunlight carries energy as visible light, infrared and ultraviolet. When it passes through a window, most of it turns into heat inside, in the floor, the furniture and the air. According to the U.S. Department of Energy, about 76% of the sunlight that falls on standard double-pane windows enters to become heat in the cooling season. Your air conditioner then has to remove that heat.
Window film reflects part of that energy and absorbs part of it in the glass, where much of it flows back outside. Less solar heat reaches the room, so the A/C has less to remove there. The effect is real, and it’s concentrated where the sun hits the glass. The Department of Energy notes that east- and west-facing windows can benefit more from these films because of their greater potential for heat gain, and that north-facing windows won’t benefit from them.
SHGC and TSER in plain terms
Two numbers describe how much solar heat gets through glass:
- Solar heat gain coefficient (SHGC) is the fraction of the sun’s heat that ends up inside, from 0 to 1. Lower means less heat.
- Total solar energy rejected (TSER) is the share kept out. It’s roughly 1 minus SHGC, so glass and film with an SHGC of 0.40 reject about 60%.
A third number, visible light transmission (VLT), tells you how much daylight still comes in. Many window films carry ratings from the National Fenestration Rating Council (NFRC), whose label shows SHGC and visible transmittance. Compare films on the same glass, and use TSER or SHGC for heat rather than an “infrared rejection” figure, which is often measured over a narrow band. Our guide to reading a window film spec sheet goes deeper.
Hypothetical example, values made up for illustration: if a clear window has an SHGC of 0.70 and the same window with film has 0.35, about half as much solar heat comes through it while the sun is on it. That’s a change in heat through one window, not a change in your bill. The bill depends on everything else in this guide.
What decides the result
| Factor | Bigger effect when… | Smaller effect when… |
|---|---|---|
| Sun-facing glass | Large east or west windows and glass doors | Small windows, or mostly north-facing glass |
| Existing glass | Clear single-pane or clear dual-pane glass | Newer low-e glass that already has a low SHGC |
| Shading | Nothing outside blocks the sun | Trees, porches, deep eaves or the house next door |
| How you use the room | Occupied and cooled through the afternoon | Closed off or empty in peak sun |
| The rest of the house | Well sealed and insulated, so the windows are a big part of the heat | Air leaks, thin attic insulation or leaky ducts |
| Your A/C | Struggles to keep up on sunny afternoons | Keeps up easily, with good airflow to every room |
How to judge it yourself
You don’t have to take anyone’s word for it, including ours. Collect a baseline before the film goes on, then compare like with like:
- Compare the same months, in kWh. Use the kilowatt-hours on your bills or your electricity provider’s usage history, not the dollar total, because rates and fees change. Compare July with last July, not July with May.
- Allow for the weather. A hotter summer uses more power no matter what’s on the windows. Note whether the months you’re comparing were hotter or milder.
- Measure the hot rooms. Put a simple thermometer in the sunny room and read it at the same time on a few sunny afternoons, before and after. Compare it with the thermostat setting.
- Check the A/C runtime. Many smart thermostats report how many hours the system ran each day. Compare hot, sunny days before and after.
- Change one thing at a time. If you add attic insulation or replace the A/C the same summer, you won’t be able to tell which change did what.
Comfort is the easiest thing to judge: whether you still close the blinds at 3 PM, whether you can sit by the window, and whether the room upstairs keeps up with the rest of the house.
What film doesn’t fix
Film changes how glass handles sunlight. It doesn’t touch the other ways a house gains heat or loses cool air:
- Air leaks around windows, doors and attic openings. Caulk and weatherstripping fix those.
- Attic insulation and ducts. Film does nothing for heat coming through the ceiling or cool air lost in the attic.
- Failing dual-pane seals. Fog between the panes means the seal has failed. Film won’t fix it, and the window should be looked at before any film goes on.
- An A/C that’s undersized or overdue for service.
- Heat through walls and the roof, which film never reaches.
What about winter?
Solar film blocks some of the sun’s heat in winter too. That’s why the Department of Energy says films are best used in climates with long cooling seasons, and why the winter sun lost on south-facing windows can offset part of their summer benefit. Houston’s cooling season is long and its winters are short, which is why solar film suits most sun-facing windows here.
For cooler months, low-e films such as 3M™ Thinsulate™ also improve a window’s insulation, so the glass loses less heat. They make the most difference on older single-pane windows. See low-e window film.
Choosing film for energy
| Goal | Film to look at | Notes |
|---|---|---|
| Cut heat, keep the glass looking clear | 3M™ Prestige | Metal-free and spectrally selective; up to 70% of visible light in |
| A stronger heat cut, slight tint | 3M™ Ceramic Series | Up to 80% of infrared rejected; compare TSER for total heat |
| Strong heat cut plus daytime privacy | 3M™ Night Vision | Up to 73% of solar heat rejected; up to 35% of light in |
| A choice of looks, clear to mirrored | HITEK architectural films | Ceramic Clear, Neutral View, Carbon View, Bronze, Ceramic DR, Silver Reflective |
| Year-round comfort on older glass | 3M™ Thinsulate™ | Clear low-e film that improves the window’s insulation |
3M figures are the maker’s published “up to” values for each series. Performance varies by shade and by your glass.
Every recommendation starts with the glass. Film absorbs some of the sun’s energy, so we check each window against the film maker’s film-to-glass guidelines first. More in window film on dual-pane windows.
Talk to Texas Tinted
We’ll tell you which windows let in the most sun and which film would cut the most heat on your glass. Send your window sizes or photos for a free estimate.
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Frequently asked questions
How much will window film lower my electric bill?
It depends on your house: how much sun-facing glass you have, the glass itself, shading, insulation, your A/C and your rate. We don’t promise a number. Compare kilowatt-hours for the same months before and after, and allow for the weather.
Is window film or new windows better for energy?
They do different jobs. New windows can fix air leaks and failed seals and improve insulation as well as solar heat gain. Film changes how the glass you already have handles sunlight, at a fraction of the cost and without construction. If your windows leak air or the seals have failed, film won’t fix that.
Does window film help in winter?
Solar film mainly helps with cooling, and it blocks some winter sun too. Low-e films such as 3M Thinsulate also reduce heat loss through the glass, which helps comfort near windows on cold days.
Get a price for your windows
Send your window sizes or a few photos through our estimate form and we’ll price the film for you, no visit needed. Prefer to talk it through? Call or text (832) 492-5314.