Other Nursery Items: Child

Humidifier in Nursery

Hi moms My 3 month old has a mild cold with a little congestion. I've heard it's good to have a cool-mist humidifier running in the nursery during the winter months, when it's dry, and have also heard one should only run it when the baby is sick, otherwise there could be a mold issue. I didn't grow up in this climate, so have no past experience to draw on. Should I run a humidifier continuously in his nursery? (We have steam heat in our condo.) Should I just run it while he's sick, or at night? Any other thoughts or experiences...