Cat flap- cold air

[ccchan]

I think we need a cat flap, but it got me thinking if there will be much more cold coming into the house if we install one? There is only one location by the front door to the side of the house where it could be installed. Has anyone noticed much difference in temperature? The outside wall is quite thick.
At the moment we just let him in-out when he wants to, the cat flap would be liberating for him (and for me).

No difference here unless it's mega windy and the wind direction blows directly at the cat flap! Then you can feel a breeze.

It's self locking so doesn't blow about generally (one of the microchip ones) and we've noticed no change in temperature in the room it's in!