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Doors and conservatories





Note: there may be a long payback period

Replacing an old door with a high-performance thermal door can keep your home warmer and reduce fuel bills, however door prices are high relative to the energy savings and you will not see cost or environmental benefits for many years.

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 may also have panels of double or triple glazing which have similar thermal properties to the windows discussed in the double-glazing section.


Money saving tips

This is a tricky one – the cost to replace a basic uPVC door may be £250, however if you are looking to install a fully insulated composite door you will have to spend £500+.

The energy saved by installing a fully insulated composite door may only add up to £15 (= 28kg CO₂) per year compared to a regular door. Financially and environmentally this is a long term project. 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’.

​Try and avoid windows

Panes of glass in your door can increase the heat loss (U- Value) and decrease its efficiency. 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 buy an insulated door, the lower the U-Value, the higher the cost. Adding glazing to the door often increases the cost and decreases efficiency.

Energy efficient doors

Environmental tips

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.

What to look for

Energy rating: Door manufacturers show the energy efficiency of their products using an energy-rating scale from A to G. ‘A’ being awarded to the most energy efficient doors.

  • U-Value: sometimes called a heat transfer coefficient is used to measure how effective the elements of the door are at preventing heat from transferring between the inside and the outside of a building ie how much heat loss it allows. The lower the U-Value the slower the heat is lost from the house and the more energy efficient the door.  Historically, older doors were made of wood, a typical 65mm wooden door would have a U-Value of 2.5. to 3 which is poor, today doors have to achieve a value of 1.8 or below to meet building regulations.
  • Doors filled with highly efficient insulating foam. These doors could help you achieve energy savings when compared to your current door.
  • 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 short wave length infra-red energy, however reflects back the long wave length infra-red radiation (heat) generated by the interior furnishings.
  • Hermetically sealed double glazed windows in the doors, this means they are airtight and reduce energy loss.
  • Composite doors: These are relatively new to the market and meet the new building regulations. To produce composite doors, different materials are used; each selected to provide a specific benefit. Materials used in composite doors include PVC, wood, steel, aluminium, insulating foam and glass reinforced plastic (GRP), which come together to produce a door that is resistant to the elements, very strong, long lived, secure and energy efficient. On the down side their CO₂e footprint may be high due to the materials used in manufacture, their transport and installation.

If you live in a conservation area or your house is listed there may be restrictions on the replacement of external doors. In such cases you should contact your local conservation or planning office to discuss the options available


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.