I keep mine in a section of the house , where this is no heating. Our house is 165 years old and double brick. Even when it is 45 degrees Celsius outside it never gets higher than 16 inside.
When setting eggs for the incubator I never use eggs more than 10 days old. I bring them inside and store them pointy end down in an egg carton below 16 degrees Celsius . The hen will often collect eggs for longer, sometimes up to 14 eggs.