Cracks at some joints after HVAC was turned on

Q: I had my 225 year old heart pine floors refinished (sanded, caulked and finished with water base satin finish). The job was done two weeks before HVAC was turned on. I now have noticeable cracks at some joints. My contractor says that it is because the HVAC was turned on causing the wood to dry thereby causing cracks. The floors have been in this environment for 25 years. What is your opinion?

A: When I lived in Toronto there was oak strip in the dining room which was 70 years old. One winter was particularly cold and long with the snow starting in early November and going right into April. So the furnace had been running for quite a long time. I noticed some gaps appearing in this floor that I had never seen before. I got the furnace installed humidifier running and the gaps went back to the way they were. So, it doesn’t matter how long a floor has been in a house, the wood still reacts to the environment. The wider the plank, the greater the expansion and contraction. I think I would buy a hygrometer and keep an eye on the relative humidity in the home. 70-75 F with RH of 35-42% would seem a good environment.