We live in Toronto, Canada. Our contractor just installed hardwood floors (maple 3 1/4 unfinished shorts which he sanded and finished after installation). There are hairline cracks between the planks. He told us that the cracks are there because the wood has dried due to the furnace being on full blast (we've had unusually cold weather the past month). He assures us that the wood will expand and the cracks will vanish once the weather warms up and moisture in the house returns to "normal". Does this sound right?
It should, its normal for the seams to open on hardwood floors during the winter months. Do you have a humidifier installed ad working? That will help reduce the shrinkage.