I'm having a problem keeping my home warm, I have a gas furnace... and noticed cold air blowing... I checked the registers, warm air blowing, but the cold air registers had cold air blowing out of them. I have to set my thermostat to over 80, but it only registers around 72 all the time... the cold air register is right across from the thermostat. Did not have this problem last winter.

Assuming when you say cold air register you are talking about the return ,which should be sucking in air when furnace is in operation. And you say its blowing out cold air? Is this at the same time that the heat registers are blowing out heat, if this is correct someone should inspect your duct work to see if someway it has fallen apart and needs to be reconnected

Yes this is what it is doing. I checked all my ductwork in the basement and it doesn't seem to be apart anywhere??

assuming when you say cold air register you are talking about the return ,which should be sucking in air when furnace is in operation. and you say its blowing out cold air? is this at the same time that the heat registers are blowing out heat,,if this is correct someone should inspect your duct work to see if someway it has fallen apart and needs to be reconnected