Originally Posted by Hube
By installing a return or two in the basement, it will make the basement's supply air stronger, thus 'slightly' pressurizing the area .
Respectfully, this is one situation in which it would be wise to consult a professional, as Wariarr suggests, to prevent endangering the occupants of the home. Here is why:
By function, a duct Return is creating a vacuum. It is incorrect to assume that this air will be supplied by the duct system. If the supply air ducts are also inadequate then the increased amount of return demand will Depressurize
this entire basement "zone" which includes the furnace.
Here is where it becomes dangerous. Since the furnace has an open combustion chamber air can be pulled back down the chimney. When the furnace "zone" gets depressurized from increased return air then exhaust gases will be pulled down the chimney
. Obviously, this puts the occupants of the house in danger of carbon monoxide poisoning!
It is extremely risky to randomly adjust the amount of return
air in any house with a furnace without consulting a professional. However, working with the supply air is safe so you might try this. Increase the supply
air to the basement then make sure that there is a large opening maintained to the rest of the home. This will introduce more conditioned air into the basement while providing a better return pathway so that this air also has someplace to go. Additionally, supply air will slightly pressurize
the basement and make is less likely that exhaust gases can get pulled down the chimney.