We all differ with diabetes and how things like heat affects us is one example of that.
My theory (and it is only a theory of which I have no evidence) is that it depends on how well you cope with the heat regardless of diabetes which dictates how it affects your BG. If you don't like the heat, find it very uncomfortable and stress about it, that stress will cause your BG to rise. Whereas, if you embrace the weather (may be easier said than done for some), you get less stressed and your BG is unaffected.
I was hearing on the radio this morning that some places are discouraging iced drinks, etc. because the body does not like sudden changes in temperature. I do not know how true this is but I know I drink water from the tap rather than the fridge.
That said, I do keep out of direct sunlight when outside and keep my curtains drawn during the day to avoid my house over heating. When I am in, the windows are open (behind the closed curtains).
I gave up on a fan some years ago as it seems to just move around hot air and not cool it down much. So I focus on reducing the opportunity for the air in my house to get hot.
Some years ago, I lived in Australia during a hot summer. Being British, when I chose my house I saw no point in air conditioning. As the temperature rose, I started to see why the Aussies spend money on it. If I was hot after work (which had air con), I would walk round the air conditioned shops, watch a movie in an air conditioned cinema or go for a swim.
If you find your BG is high in the morning during this weather, have you tried increasing your basal (long acting insulin) dose a little?