Doors and conservatories

Energy-efficient doors

Replacing an old door with a high performance thermal door can keep your home warmer and reduce fuel bills.

These doors are designed to keep the heat in and are more airtight. They can be constructed from PVC-U, aluminium, timber or a combination of these materials. They often have panels of double or triple glazing with similar properties to those discussed above in the windows section.

Benefits of energy efficient doors

  • Smaller energy bills.
  • Smaller carbon footprint.
  • More comfortable home: energy-efficient doors fit much tighter to the door frame and reduce draughts.
  • Peace and quiet: as well as keeping the heat in, energy efficient doors insulate your home against external noise.
  • Superior stability and increased door thickness gives a little bit more security.
  • Low maintenance.

High performance thermal front door.


​This is a tricky one – the cost to replace a regular door may be £100, however if you are looking to install a fully insulated composite door you may have to spend £400+.

The energy saved by installing a fully insulated composite door may only add up to £8 per year compared to a regular door so the pay back period is nearly 40 years. If you have the money then it is the right thing to do but if it is unaffordable then it may be better to buy a regular door and ensure that it is properly draught proofed – see information in the section ‘Draught-proofing your home’.

Glazing not encouraged!

Panes of glass in your door can increase the U-Value and decrease the efficiency of your door. Therefore the most efficient door is comprised of 2 sheets of steel, or carbon fibre, with a foam-filled cavity and no glazing area. When debating whether to get an insulated door, the lower the U-Value tends to mean the higher the cost, however adding glazing to the door often increases the cost and decreases efficiency.


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.

Conservatories are not thermally efficient and should not be heated.