Energy Efficiency

Double Glazed Windows create a warm and quiet home and also improve your carbon footprint. Upgraded windows will minimise draughts and heat loss. By retaining the heat you’ve generated you will save money on fuel bills and keep your home warmer in a much more efficient way. The windows and doors supplied by Dunmow Double Glazing will deliver optimal insulation. The energy efficiancy rating of our windows is nearly twice that of a single glazed window. Whatever the weather is like outside your windows will be thermally efficient and weather proof to the maximum.

How much you can save

By installing double glazing in an entirely single-glazed house you could save the following each year:

Energy rating

Detached

Semi detached

Mid terrace

Bungalow

Flat

A rated

£120 - £160

£85 - £110

£65 - £90

£55 - £75

£40 - £60

B rated

£110 - £145

£75 - £100

£60 - £80

£50 - £70

£40 - £55

C rated

£110 - £135

£75 - £95

£60 - £75

£50 - £65

£40 - £50

These savings are for typical gas-heated homes.

Benefits of energy-efficient windows

  • Smaller energy bills.
  • Smaller carbon footprint.
  • More comfortable home.
  • Peace and quiet.
  • Reduced condensation.

The costs and savings for energy-efficient glazing will be different for each home and each window, depending on its size, material and the installer you choose. Double glazing should last for 20 years or more.

To get a better idea of how much you could save by replacing your windows, use the Energy Saving Calculator on the Glass and Glazing Federation’s website, developed in conjuction with the Energy Saving Trust.

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

Energy-efficient windows come in a range of frame materials and styles. Performance criteria vary according to the following:

  • How well they stop heat from passing through the window.
  • How much sunlight travels through the glass.
  • How little air can leak in or out around the window.

What to look for

  • 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 and 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 and long-lasting, and may be recycled.
  • Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance and keeps the frame weatherproof.

Energy rating

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

U-values

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 a 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 on the glass and the gap between the glass panes.

 

Ventilation

Replacement windows will be more airtight than your 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’ve started to notice condensation in between the panes of glass in your double-glazing units then it is likely that the seal is broken, and the unit will need to be replaced.

Conservation areas

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 building and area. Double glazing can be made to look like your building’s original windows, but for any changes you do need to contact your local council’s conservation officer for guidance.

Windows in period properties

If you live in a conservation area or in a listed building there may be restrictions on what you can do to your windows. There are a number of non-intrusive window insulation options available for historic homes such as heavy lined curtains, shutters, secondary glazing and 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

Listed buildings have tight controls on what you can change on the outside and sometimes the inside as well, depending on their grading. Old sash windows in historic properties can be protected not only for their appearance but also the materials and methods used to make them. But secondary glazing can be a non-intrusive way of insulated historic windows from the inside, and may be granted permission.

There are other ways to make historic buildings more energy efficient but you will need to consult, and apply for permission from, your local planning authority.

Visit English Heritage for ways to make a historic home more energy efficient.

Sash windows

Sash window units are common features of period properties and can be a design feature. They consist of two vertically sliding frames, but are often badly fitting and 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 and 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 and 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.

Installing energy-efficient glazing

Before installing your double glazing, we recommend you check with your local planning office to see if any of the following apply:

  • You live in a conservation area.
  • You have an article 4 direction on your property, removing the right of permitted development.
  • You live in a listed building.

Doors and conservatories

Energy-efficient doors

Like any other part of the home, doors can be insulated and draught-proofed to prevent heat from escaping. Building regulations state that installing a new door requires approval from the relevant buildings control body, and new external doors now generally contain integrated insulation to reduce heat loss and 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 and the letterbox. Fitting draught-proofing to the doors and windows will save the typical household between £25 and £35 a year.

Conservatories

Even the best-quality glazing loses heat more quickly than an uninsulated cavity wall. This means that conservatories are not thermally efficient and should not be heated. Provided they are never heated, and the doors between the conservatory and the heated house are kept shut in 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, and sealed blinds or heavy, lined curtains to separate the conservatory more effectively from the rest of your house.

If you heat your conservatory, any benefit you may have had will soon disappear along with the heat that escapes into the outside air. Double glazing, blinds and shutters can all reduce the amount of heat wasted, but it is not possible to bring a conservatory up to the thermal standard of even an averagely insulated room.