depends where you are living, if in a steady climate then yes they will not all but some, as water barely fluctuates between temperatures, it stays at 25 degrees C if a very hot climate and very cold nights i suggest a heater
all my Guppies do well at 68f fluctuates between temperature of a few deggres is good for them.
Guppies can go as low as 62f only tempery not long tarm)
Guppies are best keept between 68f-74f