sensitivity to hot and cold?

I am going to be getting a Pug (11/2 years old) ...
I was not aware of the caution in regards to heat & cold... What IS TOO HOT or too cold.. especially the hot weather concerns me (I can always keep him warm enough) ... I have NO A/C... I use a 'swamp cooler' & fans... temps easily can get to 90-100 (in the house), while I am at work... I am really concerned about this!! Any suggestions?
Thank you...