Opening in cold air return

Is your basement heated by forced air? If not, I'd close that rascal.

It depends on alot of things, I leave mine open in winter to get it a bit warmer and keep the air circulating and in summer close it for AC to pull the most from the second floor return. It depends on duct sizing, moisture issues, if you heat the basement or not..

IIUC, the air in the house, the heated air that has cooled off by being in the rooms for a while, making contact with the cold windows, being diluted by cold air from leaks, etc, Is pushed out of the room my the hot air being blown into it, and is pulled out of the room by the suction of the cold air return.

ISTM a hole like yours substantially lowers the suction. Thus it cuts down on the circulation in the room and on the efficiency of the hot air fan. I wonder if, even though now there is more than ever cold air in the return, the longer more convuluted path that might arise for air return might also cut down on the circulation. Or maybe that would be counting the same thing twice.

You don't have to fix it right, with sheet metal and whatever. If it is not a flammable area, a piece of carboard and duct tape, or even duck tape, would probably last for 10 years. Then you can do it again for another 10 years.

I would definitely close it. It reduces your system efficiency, has potential of sucking in carbon monoxide, and other NG bi-products

How would it "suck in" CO? there would have to be a CO leak to begin with and that has nothing to do with the 8x8 hole that is probably just the return for that particular area.

About the only natural gas by-product it would suck in is a fart in the basement. Return air ducts have openings in every room of the house just to suck in farts and re-distribute them to the rest of the house. Now, take a deep breath and think about the furnace setup. .

Depending on air circulation in the area, a danger exists of exhaust gases being drawn into the air return. For that reason, a forced air furnace installed in a closet often must have a combustion air supply separate from the living space.

The purpose of outside combstion air is efficiency. You don't want to burn the air you just heatgead and push it up the stack.

What you say is all so wrong.

Not be scare you, but you should have your basement/house tested for Radon. If you have elevated radon levels, you DEFINATELY want to have it fixed. You don't want to blow that into your living space. If not, it's no big deal.

Oh and whilst we're at it, may just as well get all geeked out about mold also. oooooohhhh the sky is falling......

The colder outside air also has more air in the same space, right, and more oxygen. Even if it is colder.