A dirt floor in a crawl space will greatly add moisture to teh house. If the basemnt or crawl space is damp, be sure your gutters are working well, and the ground around the exterior slopes away from teh home. My biggest concern is the heater. If the dampness is there on cold dry days, that sounds like a heater problem, and that can be a life threatening situation. First I would check your chimney and heating system.
Fossil fuels give off tremendous amounts of water vapor.
Have that checked first. Seond source I would check is the basement and crawl spaces. Is there an uncovered floor or a moisture problem in any of these areas. A dirt floor in a crawl space will greatly add moisture to teh house. If the basemnt or crawl space is damp, be sure your gutters are working well, and the ground around the exterior slopes away from teh home.