Basement cold air returns

[6hoogies]

I'm planing on finishing our basement in our four year old ranch home. I have at least one heat run in the sealing of each room that we will finish. There is the main cold air return running thru the sealing. Can I just cut a vent into the main trunk to give each room that I finish and how big should they be or how many should I put in?

Thanks for your help.

[Bud9051]

Hi 6, if we ignore what you have for a moment and talk about what should be done with forced hot air, your answers should be obvious.

One of the biggest problems with FHA systems is the return doesn't match in size or location the supply. This miss-match causes some areas to have excess positive pressure and others to have excess negative pressure. Those pressures push warm air out through your walls and ceiling and pull cold air in through every little hole and crack it can find. The warm air deposits moisture in your walls and insulation and the incomming air is very dry resulting in uncomfortably low humidity inside.

Ideally, the supply and return system should be exact mirrors of each other, so what goes out matches what is coming in.

Now, for your question. Generally match the area of the return vents in each room to the area of the supply vents. There are other considerations, like size of ducts, branching, length of run, but the above will get you close.

Before you finish that basement, there are areas you will never see again, so now would be the best time to seal all of the leaks, your rim joist and all of the penetrations for plumbing and electrical up into the walls, and around your chimney.

enjoy
Bud

[airman.1994]

Return should always be bigger than the supply for sound purpose.