old house

i want to know if i can close off old cold air ducts the problem is we have no insulation in our house except what i put in can i close off some of the cold air ducts its a 1and 1/2 story house
2 of the cold air ducts are located in one room upstairs and downstairs there are 2 in one room 1 in another room and 1 in the hallway beside the front door if i close some will it affect the capability of the furnace (modern furnace) our furnace has a pipe running from the chimmney to the furnace does that mean it is drawing from the outside? sorry that was 2 questions
the reason i want to close off some cold air vents is that some are blowing out cold air
thanks sue

 

The pipe going from the chimney to the furnace is your flue, DO NOT DO ANYTHING WITH THE FLUE. That is how the exhaust gases from combustion gets out the house.

You have 2 types of vents, supply and return. If you take a piece of paper while the fan is running and put it up to a vent, if the paper is blown away from the vent, it's a supply and if the paper is pulled towards the vent, it's a return.

Your furnace is basically a closed system. What that means is the amount of heated air that comes out of your supply vents is determined by the amount of air going into the return vents. In other words, if you close the cold air duct (return vents), then you lessen the amount of heat that comes out your supply vents. Because the same volume of air that goes into the system, comes out.