1.   Besides, a duct into a gable vent will partially block the vent itself, reducing its ability to vent the attic.

2.   If the vent is blocked, the radiator will never heat up.

3.   If this area is filled, serious condensation problems can occur, and if the soffits are ventilated, it obviously blocks the vents.

4.   If these vents are blocked and snow accumulates on the overhanging eaves, warm air from the house can seep up into the attic and through the roof.

5.   The cooler air condenses into moisture, which can eat away at the innards of an older chimney and eventually block the vent with the crumbled remains.