Having Energy Efficient Windows

Having Energy Efficient Windows...

Energy efficient glazing helps reduce your carbon footprint & your energy bills, whether with double or triple glazing, secondary glazing or just heavier curtains.

Benefits of energy-efficient windows:

  • More comfortable home: energy efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.
  • Peace and quiet: as well as keeping the heat in, energy efficient windows insulate your home against external noise.
  • Reduced condensation: energy efficient glazing reduces condensation build up on the inside of windows. 

How energy-efficient glazing works:

Double glazed windows have two sheets of glass with a gap in between, usually about 16mm, to create an insulating barrier that keeps heat in. This is sometimes filled with gas. Triple glazed windows have three sheets of glass, but aren’t always better than double glazed windows. To choose the most energy efficient window, look for the BFRC rating. 

What windows are made from:

Energy efficient windows come in a range of frame materials and styles. Performance criteria vary according to how well they stop heat from passing through, how much sunlight travels through the glass and how little air can leak in or out around the window.

Glass - The most energy efficient type for double glazing is low emissivity (Low-E) glass. This often has an invisible coating of metal oxide, normally on one of the internal panes. This lets in light and heat but cuts the amount of heat that can get out. ?

Gaps between the glass  - Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass.

Pane spacers - These are set around the inside edges to keep the two panes of glass apart. For maximum efficiency, look for pane spacers containing little or no metal – often known as ‘warm edge’ spacers.

Frame materials - For all frame materials there are windows available in all energy ratings.

  • uPVC frames last a long time & may be recycled
  • Wooden frames can have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows had timber frames
  • Aluminium or steel frames are slim & long-lasting, & may be recycled
  • Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance & keeps the frame weather-proof.

Doors & Conservatories

Energy-efficient Doors - Like any other part of the home, doors can be insulated & draught-proofed to prevent heat from escaping. Building regulations state that installing a new door requires approval from the relevant buildings control body, & new external doors now generally contain integrated insulation to reduce heat loss & comply with the regulations. A properly fitted new, external door should include an effective draught-proofing system. Existing doors can be improved by fitting draught-proofing strips around the seals & the letterbox. Fitting draught-proofing to the doors and windows will save the typical household around £20 per year.

Conservatories - Even the best quality glazing loses heat more quickly than an uninsulated cavity wall. This means that conservatories are not thermally efficient & should not be heated. Provided they are never heated, & the doors between the conservatory & the heated house are kept shut in the cold weather, they can actually reduce heat loss by acting as an extra insulating layer outside your house. You can make the most of this by installing a sealed sliding door, & sealed blinds or heavy, lined curtains to separate the conservatory more effectively from the rest of your house.

Installing Energy-Efficient Glazing 

Double Glazing - The Glass & Glazing Federation (GGF) is a membership organisation whose members sign up to a consumer code, meaning you should receive excellent customer service. If you use one of their members to fit your windows but are unhappy with the work, you will also be able to use their free reconciliation service. 

Building Regulations - In England & Wales, the easiest way to make sure your windows are fitted to the Government's building regulations standards is to choose an installer who is registered with one of the official Competent Person Schemes. Installers registered with these schemes will give you a certificate when the job is finished that states your new windows have been fitted in compliance with the regulations. If you use an installer who is not registered with one of the schemes, you will need to apply for building control approval before installing the window. 

Secondary Glazing - As secondary glazing is more specialised than double glazing, there isn't currently a central body that certifies these installations. Always get a number of quotes to get the best deal.

Windows in Conservation Areas & Period Properties

Conservation Areas

If you live in a conservation area or in a listed building there may be restrictions on what you can do to your windows. These areas are of special architectural or historic interest, meaning that any work you carry out on your home must preserve or enhance the character of the area. This does not necessarily mean you cannot replace your windows, but might mean you will need to get windows that complement the character of the buildings & conservation officer for guidance. There are a number of non-intrusive window insulation options available for historic homes such as heavy lined curtains, shutters, secondary glazing, & sealed blinds. However, each historic building is considered individually so check with your local council to see what options are available to you.

Listed Buildings

Have tight controls on what you can change on the outside & sometimes inside as well, depending on the grading. Old sash windows in historic properties can be protected not only for their appearance but also the materials & methods used to make them. Secondary glazing can be a non-intrusive way of insulated historic windows from inside, & may be granted permission. There are other ways to make historic buildings more energy efficient but you will need to consult, & apply for permission from your local planning authority.

Sash Windows

Sash windows are units are common features of period properties & can be a design feature. They consist of two vertically sliding frames, but are often badly fitting & made of single pane glass so have poor insulating properties.

If you want to insulate your sash windows there are a number of alternatives to conventional double glazing. If you want to keep the design & look of the sash windows, there are units available that are in keeping with the original design; these are fitted and sealed to prevent draughts & incorporate double glazing to reduce heat loss.The frames don't need to be plastic, but can be metal or wood with an insulated core.

An increasing number of double glazing companies offer double glazing in period properties. Replacing sash windows can be expensive, so good-quality secondary glazing may be worth considering.

Alternatives to Double Glazing

If you can't install double glazing - for example, if you live in a conservation area, period property, or listed building - you can install secondary glazing, or use heavy curtains, or do both. 

Secondary Glazing

A secondary pane of glass & frame can be fitted inside the existing window to reveal. This won't be as well sealed as a double-glazing unit, but will be much cheaper to fit, & will still save energy. Low emissivity glass will improve the performance of secondary glazing.

Secondary glazing kits are available for the proficient DIYer - these cut down on costs & are a non-intrusive way of insulating your windows.

Curtains, Sealed Blinds & Shutters

Curtains lined with a layer of heavy material can reduce heat loss from a room through a window at night & cut draughts. Hollow blinds, fitted into place with a sealed frame, & sealed shutters will also help cut draughts & keep your heat for longer.

Understanding Energy Ratings 

Some window manufacturers show the energy efficiency of their products using an energy-rating scale from A++ to E. The whole window (the frame & glass) is assessed on its efficiency at retaining heat. The scheme is run by the British Fenestration Rating Council (BFRC). 


Windows that have an energy rating will have the u-value of the window displayed on the energy label. A u-value is a measure of how easily heat can pass through material. Materials that let out more heat have higher u-values whereas materials that let less heat pass through them have lower u-values.

In some cases, windows with a higher energy performance rating might have a higher u-value than windows with a better energy efficiency rating. This might seem the wrong way round as lower u-values indicate better insulation levels. However, in these cases it will be that there are other aspects of the window that make them better overall such as coating used in the glass & the gap between the glass panes.


Replacement windows will be more airtight than you original frames, so condensation may build up in your house due to the reduced ventilation. If your house does not have much background ventilation, look for replacement windows with trickle vents incorporated into the frame to let in a controlled amount of ventilation.

If you start to see condensation building up around your windows, there may be a damp problem in your home. As a general rule, damp occurs when there is inadequate ventilation, inadequate heating, inadequate insulation or a combination of these. If you have started to notice condensation in between the panes of glass in your double-glazing units then it is likely that the seal is broken, & the unit will need to be replaced.