Curtains, particularly thermal lined ones, can reduce heat loss by as much as 60%, depending on the type of windows your home is fitted with.
The key to ensuring you get the most out of your curtains is in understanding exactly how heat is lost, and how the use of thermal lined curtains can prevent this.
Understanding the physics
You know the old saying that hot air rises? Well, during cold weather that is exactly what happens, and something called the reverse chimney effect comes into play.
It is widely accepted that cold air is denser, and therefore heavier, than warm air. When it’s cold outside the air close to the window is cooled and sinks down (due to its density increasing with the temperature change). When the cooled air sinks it’s replaced by warmer air from other parts of the room.
As you can imagine, this then creates a circulating current, taking all of your warm air and replacing it with cool air. And just like that, you have lost most of your heat, not just near the window, but in the entire room.
How do curtains help?
Well in some cases, curtains can actually make the situation a whole lot worse. If your curtains are not fitted correctly they form a channel between the window and the curtain, creating a space for the cooled air to sit and increasing the effect of the reverse chimney.
The most important aspect to note is that it is the power of each factor combined, which decreases heat loss. No single factor works in isolation.
The first thing to ensure is that your curtains fit your windows correctly. This means that they are within a millimetre of perfect, with absolutely no gaps at the top or bottom. They need to fit against the wall snugly, creating a seal between the curtain and window.
There are two options when it comes to thermal fabric. Either, you can have a curtain that is made from a thermal coated fabric, or you can have a separate thermal lining, which sits behind the regular curtain.
Thermal coated curtains are better than nothing, but having a separate thermal lining provides a whole new level of protection.
With thermal lining, a warm air pocket is created between the lining and curtain, providing additional protection from the reverse chimney effect.
You can even go one step further to increase the insulation level by having an interlining such a bumph put in between the curtain fabric at the front and the thermal lining at the back. It simply creates another warm air pocket and is great in really cold parts of the country.
Once you have your curtains fitted, make sure that you close them before it gets dark. This allows you to utilise the warm air that is already trapped inside your house.