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Windows can be sources of large amounts of lost and wasted heat for a building whilst simultaneously letting colder air in. If a building has large windows or there are many of them, this can cause a poor thermal environment, requiring more fuel to be consumed to maintain a comfortable heat. This guide outlines ways of minimising heat lost through your windows.

Secondary or double glazing

Installing secondary or double glazing is one of the most effective ways to reduce heat loss through windows. Secondary glazing adds an additional pane of glass to the inside of existing windows. Double glazing is two panes of glass with an airtight vacuum in the middle. This can be filled with an inert gas like argon. Both are more effective at heat loss reduction than single glazed windows however, double glazed windows requires manufacturing and installing of new windows and the disposal of old ones. This makes double glazing unattainable for most museums located within listed buildings or conservation areas.

Internal secondary glazing and draft proofing of existing windows can be as effective at minimising heat loss as double glazing while still retaining the external character of a listed building. Planning permission from your local authority is still required for internal secondary glazing.

Historic Environment Scotland and Historic England have published advice on window management for energy efficiency in historic buildings.

Managing Change in the Historic Environment: Windows – Historic Environment Scotland
Energy Efficiency and Historic Buildings: Secondary glazing for windows – Historic England

Draught proofing windows 

Similar to other sources of ventilation, windows can cause excessive and unnecessary draughts in a building. Draught proofing windows can be a cheap and effective way to improve energy efficiency as well as reducing dust ingress and noise reduction. 

Windows can be draught proofed by: 

  • Self-adhesive foam strips- cheap and easy to install but may not last long. 
  • Foam sealant- can be sprayed into gaps around windows. 
  • Metal or plastic strips with brushes or wipers attached – long lasting but cost a little more. 

More information can be found at: 

Adding shutters, blinds, or thermal curtains

Installing internal shutters, blinds, or heavy, thermal curtains (especially for larger windows) to windows can be an affordable and effective way to help reduce the amount of warm air lost. Research from the English Heritage found the following results in heat loss reduction through windows: 

  • Plain roller blind = 38% 
  • Heavy curtains = 41% 
  • Honeycomb blind = 51% 
  • Well-fitting shutters= 58% 

The study can be found at:

Research into the Thermal Performance of Traditional Windows:Timber sash windows | Historic England