Re: Heating and air
Ideally yes having a cold air return is benifical for conditioning the basement.
It should come directly from the return air plenum at the furnace or the return air trunk --- don't tap off the return upstairs.
The same applies to the supply vents --- they should be off the supply trunk and not tapped off supply runs upstairs.
The returns should be placed as low to floor level as possible in order to help draw the warm air from the supplies which are likely to be at ceiling height. Another benefit is drawing the colder air from the floor level helping to make the space more comfortable.
Typically the number of returns is roughly half than the supplies to keep the basement at a more positve level so as not to upset the combustion equipment air intake.
Example--- depending on walls and rooms with doors ...... 4 - 6 inch supplies = 2 - 6 inch returns
Hopefully this helps.
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