My floors are just about one year old. In the past 2-3 months large gaps are showing up all over the floor. I'm not concerned about the smaller cracks, but am very concerned about the ones visible from a standing position - some are wide enough for a quarter to fit into. Even the steps have a gap where the floor meets the riser. I also have a few boards that have split. You can hear the popping anywhere in the house. My builder is blaming it on not having a humidifer. Is this correct?[list][/list]

I agree with the builder, to some extent... Get a hygrometer, and let us know what the humidity actually is inside the dwelling.

Wood being hygroscopic, swells with a gain of moisture, and shrinks with a loss of moisture. Your floor has lost moisture since it was installed. Your running the heater, which pulls all the humidity out of the air inside the dwelling. This dries the wood out, and it shrinks. Yes, it can shrink a lot. Especially boards wider then 2¼" and the wider they are, the worse the gaps become.