Our house is on a crawl space and we've closed all the vents around the outside of the house and replaced a filter. Yet there is still cold air blowing from the floor vents. What can we do?
The thermostat is set on emergency heat and has been like that for the about 8 hrs. The fan option is on auto.

Is this a electric furnace?

Yes it is.

Make sure all the circuit breakers are turned on both in the house electric panel and on the furnace itself.

Were you in this home last winter and did it heat OK then?
Is the weather in your area more severe right now than normal? In other words is it colder than normal?

I am saking these questions because it is possible the heater is to small for your home OR that one or more of the heat strips is broken.