@Laotionne - You are right about the typical bathroom exhaust fan sucking warm air from a home, however, there is a solution. Instead of buying the conventional exhaust fan, you can spend more money and purchase a heat-exchange ventilator fan.
These heat-exchange fans use the warm air that is being sucked out to heat the cooler air that is replacing it. This way the exiting air and the energy used to heat it is not being wasted. This type of fan can cost twice as much as a regular bathroom exhaust fan, but that cost should be weighed against the money you will save on heating your home.