It's actually because of the wind this time. It's been really quite windy (gusting into the 30s for a couple of days now) and it's been warm or very warm. That warm air gets blown into the airbricks and the cavity downstairs, and - as is quite common in an oldish house like mine - there are the odd draughts. Normally that's a good thing (keeps air changing in the house, reduces mould etc), but not in the very unusual situation of it being very warm and windy - that certainly doesn't happen often!
Even in the recent heatwave it took a good 3 days or so for downstairs to warm to uncomfortably high (26C+) levels, but once it got there it stuck there for a while (aside from when I set the a/c to blow along the upstairs hallway, it then bounced off the landing wall and cooled the dining area / kitchen down nicely).
Originally Posted by: Retron