Ah jumper.. I have been to Paris many times in August..
And what can I tell you.. totally unpredictable..
Yes, it is usually hot. And problem is there are rarely any breezes ( I live on coast where there is air movement) .. and worse yet.. I find street noise precludes me leaving windows open all night( and forget screens on windows.. never seen them )
BUT .. a few years ago took a friend in August.. Told her to pack sundresses, capris, light cottons etc..
We were cold and wet for 7 out of 9 day visit.. lol.. we had to go buy some more long sleeved shirts etc..
So its a crap shoot.
I never book a hotel or apartment in summer without a/c though.. because when its hot in Paris its nasty hot.. and you are outside all day long.. and most/many public buildings are not a/ced.. so you have no heat relief.. the streets and all the buildings ..all that pavement reflects the heat at night.. it can be gross.
If you decide on an apartment without ac be careful to avoid any top floor apartments(ovens) make sure there are plenty of windows on opposite walls for hopefully some cross breezes,, avoid ground floors ( so you can leave windows open) .. check out sun exposure .. afternoon sun bad..
Parisbestlodge has some apartments with ac. I am using them again this summer.
PS if you are from a place that is regularily very hot and you manage without a/c then you may do better then I .. hot to me is over 80-85.. and not cooling down to 75 at least at night..