IMM wrote:

"Ian Stirling" wrote in message
...
IMM wrote:
snip of letterbox
Seal it up. Letterboxes allow draughts in. Eco doors do not have them.
Fix a
key mailbox on the wall outside. They also look better.

Letterboxes do not have to let draughts in.
Some have properly formed gaskets round the door, and seal tightly
until opened manually.

Eco doors are fully insulated. The letterbox is a large cold bridge, also it
is difficult to make air tight. Best get rid and fill the hole.

The letterboxes heat loss is utterly trivial.