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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. 

Secondary or double glazing

One of the most effective means of improving this issue is secondary or double glazing of windows. Secondary glazing is where an additional pane of glass is added to your existing window on the inside. Double glazing is two panes of glass with an airtight vacuum in the middle, which can be filled with an inert gas like argon. Both are more effective at heat loss reduction than single glazed windows, but double glazed windows require the manufacturing and installing of new windows and the disposal of old ones, whereas secondary glazing upgrades your existing ones. Double glazing is usually more expensive and saves more heat over the long term compared to secondary glazing. 

More information can be found at: 

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