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Are Exterior French Doors Energy Efficient?

The addition of exterior French doors can transform any room. They have many glass panels which welcome sunlight to brighten the space, while the classic design of the frame can add a traditional farmhouse feel to any rustic room.

But they can also feel like a big change, and change can be intimidating. It can even spark a thousand questions before you feel ready to commit to it. You might wonder how secure French doors are, or ask are French doors safe for your family?

Another question you should ask is whether French doors are energy efficient, which is why we’ve put together this post. In it, we’ll explain what energy efficiency is, how it’s measured and whether French doors really are an energy friendly choice. 

Exterior French Doors U Values

The term energy efficiency means using the least amount of energy possible to achieve the biggest possible effect. It’s easiest to grasp when it’s used in relation to appliances like lightbulbs: an energy efficient bulb is one that gives the optimal amount of light while using the least amount of electricity possible.

When it comes to French doors energy efficiency, they are judged by how good they are at insulating a room. Another way of saying this is how well they prevent heat from escaping through them. If French doors are energy efficient, less energy is needed to heat the room they are in, by keeping the already warm air inside.

Energy efficiency for French doors is judged by its ‘U value’. In actual fact, energy efficiency of all doors and windows is shown by a U value, not only French doors.

The U value for French doors is measured in watts per square metre Kelvin (W/m2 K). As the U value of the door represents how much heat is lost through them, this means the lower the U value for a door is, the more energy efficient the door is. Or the better it is at keeping warm air inside the room.

The perfect exterior French doors u value rating would be 0, meaning the doors lose no heat (energy) through them at all. Of course, this level of perfection is not a realistic expectation. Average external French door u values sit at around 1.8W/m2 K, though here at Vibrant Doors some of our external french doors have u values as low as 1.4W/m2 K!

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Are French Doors Energy Efficient?

There is no denying that French doors are among the most attractive doors you can have in your house. They’re stylish in design, giving a charming traditional vibe to any property.

They can also improve the aesthetics of any room by maximising the light and space within it. The large glass panes they feature allow sunlight to flood into the room, while also showing the views of outside to their best advantage.

And this is just when the doors are closed; when they are open, the great outdoors is welcomed into your room. This doesn’t just make the room lighter and brighter but lifts the mood of the space as well. 

But, whenever you’re looking to install or replace the doors of your house, energy efficiency should be one of your primary concerns. Not just because no one wants to be wasting money paying heating bills on a house that haemorrhages hot air. These days there are even building regulations around energy efficiency requirements.

If you’re drawn to the classic styling of French doors, you’ll need to ask, are exterior French doors energy efficient? And you’ll be pleased to know the answer is yes, they can be incredibly energy efficient (especially here at Vibrant Doors!). That is, as long as you buy a high-quality, well-constructed set of doors.

This is because a lot of different factors will affect how energy efficient any door is. 

It is about more than how thick your external French doors are, or even what they’re made of. For example, how well a door fits in its frame will have a massive impact on how much heat it allows to escape.

Warm air will get out of any gaps around a door, so a badly fitting frame will make any door energy inefficient. Especially as these same gaps will also let cold air in.

The materials and construction of a door are potentially the biggest contributors to its energy efficiency. This means French doors can vary in their u value, depending on what they are made of.

One of the defining features of French doors is the glass panels in them. The composition of these panels can make a big difference to a door’s u value. If you choose doors with toughened, double-glazed panes, you can be confident that no unnecessary heat will be lost through the surface of the panes. Doors with fibreglass panels will be even better insulators.

Another consideration is the composition of the door itself. These days, many people chose to have uPVC doors due to their superior u values. People favour this high-performance plastic because of its excellent insulating skills. Plus, there’s the fact that it's durable, strong and cost-effective.

Still, there is no denying that solid timber and wood make for a far more attractive door. It’s fortunate then that wood can be treated or laminated to make it more weather-resistant and more insulating without sacrificing the rustic, charming look of the surface.

As long as your French doors are of quality construction and installed correctly, they should achieve an excellent seal where they meet. If over time this seal seems to weaken, and you are concerned that drafts are coming through, there are a number of troubleshooting tips you can try to help realign your external french doors.

Are Sliding Doors or French Doors More Energy Efficient? 

If you’re looking to brighten or broaden a space, a new set of doors could be the answer. Any door constructed with a high proportion of glass will leave a room soaked in sunlight, giving it a cleaner, happier feel.

French doors are perfect for this task. Their panelled construction allows all the sun’s rays in, while a French door’s distinctive appearance adds a fresh, farmhouse aspect to your decor.

But if loads of light is what you’re after, you may also be drawn to sliding doors. Installing these vast glass panels can really break down the barrier usually created by the walls of a house. And, while they might not look as classically chic as French doors, sliding doors are still guaranteed to let light, and the great outdoors, into your home.

If you’re struggling to choose between the two types of door, then the question ‘are French doors more energy efficient than sliding doors?’ could be a decider. 

As we’ve discussed, French doors can be very energy efficient. Unfortunately, sliding doors don’t tend to be. Those lovely glass panels that let in all that lovely light are bad at insulating. Glass itself isn’t a great insulator, so the more of it a door features, the less heat it will keep in.

In comparison, wood and timber are great insulators. French doors have a good balance of glass to wood in their frames which makes them far more energy efficient than your average set of sliding doors. 

A high-quality set of French doors will also come with a strong seal around them. This will plug any gaps between the frame and the door, keeping even more heat in and lowering their U value further. 


The energy efficiency of external French doors is not a simple thing to pinpoint. It depends a lot on of factors, and can’t really be looked at in isolation. We hope this post has given you a good overview of all the factors you’ll need to consider when purchasing French doors, to help ensure you get external doors that are as energy efficient as they are attractive.

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