Our friends at Better Building Works have some information on the impact that leaky, dirty, and poorly maintained duct work can have on your home’s health:
Pressure difference can bring dirty, dusty air into the duct system and distribute it throughout the home or office through supply vents. This dust can aggravate allergies. Worse, if there is mold or other allergens present in attics or crawlspaces, well, you’re breathing that too.
There’s more at the full post but the recommendation is simple: get your ductwork reviewed and cleaned as you get ready to close your home up for the winter. Not only can getting leaky ductwork repaired save you money on your winter heating bills, it can make sure the air in your home is the healthiest possible.