I checked. It wasn't.
So where was the cold air coming from?
It was coming from the electric heater. I'd turned the fan on but not the elements and it was in generating a nice, cooling, summery breeze.
This bitter weather isn't going to last much longer. It's the beginning of March for Pity's sake! The forecasters give it until Sunday and then the thaw should begin. The snow is beginning to look shop-worn and has blown out of the trees. It may feel colder than ever but the instruments say otherwise. The temperature is still below freezing- but only just. The horses had broken the ice for themselves and all I had to do was top the butts up with a succession of bucket loads from the kitchen tap.
The daffodils were about to bloom when this lot hit. I wonder what state they'll be in when it goes away?