1994 Modular Bathroom and stove vents/fans

[miladyelfn]

Hello, I own a 1994 Modular home. When we were doing some renovations the builder told us that our bathrooms/kitchen vents vented straight to the roof which was up to code at the time of build. However, once winter hit we realized that cold air blows right down those vents! BRRRR! Is there something relatively easy we can do to stop the downward airflow (don't want to leave the fans running constantly if possible)? Just until we can figure out a what a long term solution might be. Thanks.