Make sure your building is properly sealed and ventilated
For comfortable interior conditions all year round, it’s important to achieve the right balance of sealing (for energy conservation) and ventilation (for healthy indoor air quality) in your building. Keep windows closed to conserve heat during the winter, and make sure ventilation shafts are in working order.
http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11830