Hello terri06
Without having the details involved in your guppy fry as to if they are a true breeding strain that you bought (knowing this is a major factor) or if they are from local petshops where you probably wont get fry that look like the adults (depending on genetics of female and male) and if they are related there could be several answers to this question.
How is your room heated is one.. if electrically heated the temperature would fail with a power failure as well as any heater that you put in the aquarium
If it is gas heated or other means you may find that room temperature may be too low for the fry tank (check with thermometer)
I would go with the idea of getting a heater for the aquarium with a sponge filter for the fry tanks as it is generally what professional breeders would do (Do this especially if they are true breeding strains)
Otherwise you can follow the good advise of DanDamage92 and get floating plants for the fry to hide in generally but not all the times guppy fry can escape parents but if you have any other fish that could be predators of the young I would definately put them in another aquarium ...