When it is a real tepid day out & you have no air conditioning it can be a undoubtedly terrible & potentially deadly thing depending on where you live in the country, then some locales can get by with no air conditioning on a tepid day with just a fan if you live in a gradual temperature where it does not get above 90 degrees as a tepid day, & then it cools down at evening. But if you live in a locale like Arizona, you will need to have some form of undoubtedly powerful air conditioning twenty four hours a day & seven nights per week or you will surely die. Because uneven temperatures there can get up to one hundred & twenty degrees! It is seriously deadly. And separate from air conditioning there is no survival. I have lived in that section of the US of america before. And it is no fun let me tell you! Even if you have the most top of the line, brand new, up-to-date & extremely overpriced central heating, ventilation, & A/C, the heat can get to be so damn terrible that even the air conditioning out of one of those top quality systems will even not be great enough. You will have to sporadically have a portable air conditioning to help cool your home & the air conditioning from your central heating & cooling system unit! But thankfully I do not live there anymore & in the event I have a serious air conditioning breakdown, I could get by with a fan for one single day & evening. But I feel for those who can not.