Remove cold air return?

[gusaroni]

I recently bought an 1100+ sq ft ranch with an oil/hot air heating system. It was orignally a 4BR, but has been converted to a 3BR with the space being added to the living room. The added space resulted in the LR being roughly 15' x 25'. Because there was a wall removed, there are now 2 12" x 8" cold air returns in the floor about 18" apart. I'm in the middle of putting down a new floor in the LR, and I'd like very much to remove one of these returns. One of them is directly in a primary traffic area, and now that the space is all one room, it seems like one return should be enough, but I don't know whether I'd be messing up my system and/or furnace if I remove one of them. There is one other 12" x 8" return at the other end of the house (in the hall by the BR's).

Can I get away with eliminating this return?

[N74TG]

Is there any way you could move one (or both) of the ducts to a more out-of-the-way area? Where does your return air duct run? If it is a short duct that runs straight into the furnace, you're probably out of luck, but maybe there is enough length to it that you could place returns elsewhere.

If you do decide to move it I think I would not reduce the size any. If fact you're unit will probably run better (more economical and last longer) if you enlarge the return air vent and duct.

While you're at it check the "return" from each bedroom back into the main living area of the house. This return is usually the gap at the bottom of each bedroom door. Even a 1" gap is probably not large enough (though most people have more like a 1/2" gap). Without a good return gap under the doors your bedrooms "pressurize" (ie go to positive pressure), which depressurizes your main living areas (kitchen, living room, central hallway, etc). Depressurizing is bad, as it can result in backflow of combustion products from your gas (or oil) fired water heater or furnace if the unit is near the main living area. Instead of the combustion products going up the flue (like they're suppossed to do), they can backflow into living areas. Carbon monoxide is colorless, odorless and deadly.

If you choose not to address bedroom pressurization and living area depressurization, please at least install a carbon monoxide detector, and check the batteries regularly. Better yet, buy one that's powered by 110 volt AC with battery backup. Relying on the old adage that "it's never been a problem before" won't fly if you go to modifying things in your house.

I know this is a long post, probably much more than you ever wanted. But making what appears to be "simple" changes to heating and cooling can cause unexpected results and problems in other areas. Start educating yourself by reading the stuff at buildingscience.com; start with the air conditioning, heating and ventilation topics. I know it's a lot of material, but if you're going to DIY you need it.

No, I do not work for Building Science or have any vested interest in the company; and no, I am not a licensed heating or air contractor either. I'm just a simple guy trying to build his own house; so to a certain degree you should even take what I have to say with a grain of salt. If in doubt, consult a pro (and by pro I mean an hvac engineer, NOT a heat and air salesman).

good luck

[gusaroni]

Both of the returns are about 10 feet long, so I may be out of luck there. I could relocate one of the returns to somewhere out of the traffic flow, and still in the LR. I'm trying to avoid this though because it will mean crossing joists in the basement, and I'd rather not lose the headroom in the basement...although, that is preferable to backflow.

Could I just leave the return open in the basement? It wouldn't help the convection upstairs at all, but it would continue to provide the same intake for the furnace...I could even make it bigger if I left it downstairs.

By "Open", I mean properly connected and filtered...not just "open".