What Makes A Window Energy Efficient?

What Makes A Window Energy Efficient?

By upgrading to energy efficient windows in your home, great savings on heating bills can be achieved. This article will act as a handy little guide to help make you more informed on what makes a window energy efficient .

Window Frame Material

The material in which your window frame is constructed from has a big impact its energy efficiency:

  • PVC: Due to its low cost, versatility, durability and energy saving qualities, PVC Windows are generally considered the ideal option when upgrading windows. PVC has a low thermal conductivity and will not suffer to the same heat loss as aluminium. As PVC as a material is so versatile, it can be moulded into many different forms and shapes.  Energy Efficiency is a balance between energy savings and cost, and it is this factor which places PVC above timber, as PVC Windows are typically cheaper than timber, both in initial cost and long term maintenance. This means that the possible savings in heating bills acquired through timber will not be realised due to high installation costs. If you are looking for the benefits of PVC but want the appearance of wood, check out our Residence 9 range.

  • Aluminium: Aluminum is an excellent conductor of heat, and when discussing energy efficiency, that is not a good thing. The conductive nature of aluminium will mean it is more susceptible to lose heat and thus cost more for you to heat your home.  Modern Aluminum products are far more thermally efficientthan ever before, they typically include thermal breaks and multiple chambers to combat its inherent conductivity.

  • Wood:  Wood or Timber, is generally considered to have the lowest heat loss of all the materials, which means it is great for energy efficiency. However, Timber is nearly always a more expensive option and is less versatile in terms of appearance than aluminum and PVC. Timber windows are also susceptible to warp and rot which will increase their maintenance cost and reduce lifespan.

Argon Gas Between Panes

A Rated Energy Efficient PVC Window Installed by McMahon and Nagle

If you opt for A Rated double or triple glazing, they will have Argon Gas inserted between the panes. This gas is relatively inexpensive, non-toxic and is becoming more common in residential windows due to its energy saving and soundproofing properties.

A U-Value is used by the likes of the NSAI and BFRC to measure how well a window prevents heat from escaping. The lower the U-Value, the greater a window’s resistance to heat flow and the better its insulating value. Argon Gas will reduce the U- Value of your Windows and provides more thermal efficiency than having air between the panes and acts as an added insulator.

Low E Coating On Glass

Low E is an incredibly thin, transparent coating which reflects heat. It was developed to minimise the amount of ultraviolet and infrared light that passes through a window, without reducing visible light. This means that the only way you will notice this coating is in the energy savings you’ll receive and the increased comfort of your home.

Low E coating effectively acts as an insulating barrier to ensure heat remains inside your home during winter, and that warm air is reflected out during summer, to prevent overheating. The application of Low E coating will reduce the U-Value a window.

A Rated Energy Efficient PVC Window Installed by McMahon and Nagle Using Leadlite Retention to Achieve Period Look.

Double / Triple Glazing & Glass Thickness

In essence, a double or triple glazed window is a window with either two or three panes of glass with an air or gas space in between. These extra panes of glass provide greater insulation and thus improve energy efficiency. Typically windows can be the weak spot in the building envelop and that is why the extra insulation provided by Triple Glazing can be popular.

Triple Glazed windows improve insulation and this can be measured by the U-Value of a window. For example, Single Pane Windows have an average U-Value of 5, older Double Glazed Windows tended to get a score of 3, modern Double Glazed Windows score 1.4 but Triple Glazed Windows can score as low as 0.8.

In a previous section we discussed the benefits of Argon gas between the window panes and these benefits can be maximised with triple glazed windows due to the extra gas space. Similarly, triple glazed windows allow us to add more Low E coatings. Triple Glazing allows us to apply 2 extra coatings of Low E, which will significantly lower the U-Value and improve energy efficiency.   Not all window companies use 2 panes of Low E glass so it is worth checking this specification with any potential supplier.

It is important to note the overall thickness of the Double or Triple glazed units you are planning to have installed in your home. Unit thickness will have a major impact on the energy rating  / performance of a window.  Older window systems can only take 28mm units, whereas more modern systems can take from 36mm to 44mm.  The thicker the better!  Our’s is 40mm.

Spacer Bar


A Rated Energy Efficient PVC Windows Installed by McMahon and Nagle.

A spacer bar is the continuous hollow frame that separates the two glass panes in a double glazing window. These were traditionally made of aluminum, which is more susceptible to heat loss and condensation, both of which are detrimental to window performance.

New Spacer Bar Designs are part of what is called warm edge technology, and are built using PVC, which has a low thermal conductivity These spacer bars conduct less heat than metal bars and increase the resistance to heat flow from the warm side to the cold side of the window, reducing the potential for condensation.

About McMahon and Nagle

McMahon and Nagle are the experts on energy efficient windows and doors in the Dublin area. Our 35 years of experience ensure we provide the cutting edge in design, quality and security. For more information, please call our team on 01 – 846 0364