adunephel

my house is one level, on a concrete slab, open floor plan (big open room, few doors), forced air heating/cooling (i believe). house inspector said i needed to have cold air returns. my furnace is located in a utility room with a completely slatted door.

could someone explain why i would have to have returns? (to me all the cold air gets sucked back up through where the air filter is).

thanks

paul52446m

A furnace running like yours is pulling a vacuum on the room the furnace is in. This can cause a down draft in the furnace stack and water heater stack.
If you have a natural draft furnace you could suck the flame out the front of the furnace . So you could have a fire risk and also a risk of getting carbon monoxide in the home If you check the size of the opening where the return air goes into the furnace. The free area going into that room has to be 4 times greater to not pull a vacuum. So check that slatted door and tell me how many sq. in. of free area you have. Paul

adunephel

the slatted door is 66x24 (1584 in2), the air filter is 16x24 (384 in2)

paul52446m

When i say free area, that means the open area. The slates on your door is probably about 1/8" by 20" , so that means it would take 8 slates to make 1" which would be 20 sq. ". Your filter free area would be about 308 free area
Paul

adunephel

gotcha:
the door has about 186 in2 then.
the door itself is not tightly sealed as well, open spaces at the top and bottom.

paul52446m

This was a old formula that is a safety factor, but if you are not going to duct the return out that you should use it. New code will say you must duct the return out of that room, Be safe, Paul