My furnace is blowing cold air instead of hot air - wha twould cause that?

You are going to have to give me more information than just what you wrote. I could answer that by saying you have no fire I the furnace.

So what I would like to know is this a gas furnace or an electric.

How old is the furnace and what brand.

Do you have a small motor that comes on when you turn the thermostat up to heat.

If you have and AC system does it work now.

Give me some answers and I will try to help.