It's been sat running in the attic for a few weeks now, along with another one, basically they upload to a MYSQL database on my webspace, and I've been playing with graphing options.
So I just grabbed it one from the attic, and stuck the BME280 in the top of the freezer, it's on wires away from the ESP8266 (or the ESP heats it up) so that went inside, the ESP and battery stayed outside.
I was pretty impressed how fast the temperature came down, 20 minutes and it was good to go.