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Internal Bi-Fold Doors Thermal Efficiency

When shopping for internal doors, it’s important to account for how they look alongside the rest of the interior, and how well they function.  But just as important is the energy efficiency – particularly if a door is bordering an area of the house that isn’t normally kept as warm as the rest of it.

This concern is just as pressing with internal bi-fold doors – and for larger ones, it’s even more so, as the larger the door is, the greater its role will be in preventing heat from transferring from one place to another.  In this article, let’s examine how we can ensure that our bi-fold doors are effective insulators.

Why is thermal efficiency important?

If we’re going to save money on our electricity bills, it’s vital that warm air stays where we’d like it to be. Heat that escapes through poorly-insulated doors, after all, is heat that’s going to need to be replaced.  And it’s the homeowner that’ll need to cover the cost of this replacement.  Far better, then, to invest in a door that will slow the transfer, and save money in the long run.

There are also good environmental reasons why an energy efficient door might be preferable to a non-energy efficient one, as the more energy we consume, the more pollution we consume as a by-product of that energy generation.

While it’s usually external doors which are required to do more of the heat-excluding work than their internal counterparts, it’s still worth considering the value of an energy-efficient internal door.

How is thermal efficiency calculated?

You might have seen the energy efficiency of a door or window described using the ‘u’ rating.  Most commonly used in windows, this figure will help you to choose between a poor insulator and a decent one.  The same can be said of ‘r’ values, which are more commonly used to refer to walls, floors and roofs.  The two figures tend to be arrived at under different assumptions, and so comparisons between the two are tricky:  u-ratings measure the rate at which heat is lost, while r-rating measure the resistance to that loss.  Lower u-ratings are better, higher r-ratings are worse.

In order to simplify things for the average consumer, thermal efficiency is often instead put in terms of a rating from A-G (and an accompanying coloured stripe).  An ‘A’ rated door will perform much better than a ‘G’ rated one.

How else can we improve thermal efficiency in the home?

If we’re interested in spending less energy in our homes in general (particularly during the winter) then there are a myriad of different ways of doing so.  Some of them involve major investment, others can be done for very little.

Measure your doors

When we’re first installing our internal bi-fold doors, it’s important to ensure that the door closely matches the dimensions of the gap we’re installing it into.  This will provide minimal space for cold air to pass through at the edges.  If you’re the owner of a larger property, then some areas, like garages and utility rooms, might not need to be heated quite so often.  By measuring precisely, and investing in a close-fitting door, we can minimise the space through which cold draughts can pass.

Close curtains

Since windows are the weakest point of a building when it comes to thermal efficiency, it’s essential to close curtains in the evenings.  This will help to impede warm air, and thereby minimise heat-loss during the night-time.  Then, when morning breaks, open the curtains and allow sunlight to enter your home again, heating it.

Heavier curtains are more thermally efficient than lighter ones, so be sure to invest in them.  This is especially true in properties in conservation areas, who might lack the necessary permissions to install double-glazing.


Standard glazing technology is a notoriously poor insulator.  That’s why the installation of double-glazing can have such a marked impact on the performance of a window, and by extension the entire building.

Double-glazing works by sandwiching a layer of inert gas (usually argon) between two panes of glass.  This dramatically slows the transfer of heat from one side to the other.  Double-glazing can be of tremendous benefit not only to the windows of a building, but to any windows that might be contained within a door – both the internal and external sort.

Cavity Wall and Loft insulation

Using a similar principle, it’s possible to improve the heat-retaining properties of walls and roofs, too.  A cavity wall is one which consists of two separate walls, with a space in between known as a cavity.  By filling this space with a special expanding foam, it’s possible to greatly improve its u-rating.  The same is true of our loft, through which most of the heat in our homes escapes (as it rises).  Cram a suitable amount of insulating material into a loft, and you’ll prevent that heat from escaping so easily.


We rightly concentrate our energy-saving efforts on external doors at the expense of internal ones, since the former are expected to preserve far greater differences in temperature on either side.  That said, there is still a great deal to be said for ensuring that our internal doors are substantial and draught-free.  In order to do this, we should ensure that we invest in doors with low u-ratings, and whose dimensions closely match those of the surrounding frame.  In doing so, we’ll contribute to the overall energy-efficiency of our homes.


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