A furnace blowing cold air is one of the most common heating complaints in Alberta winters. Often the fix is simple: the thermostat fan may be set to "ON" instead of "AUTO", or a dirty filter may be making the furnace overheat and shut off the burners. In other cases, a flame sensor or ignition problem is the cause. Sherwood Mechanical explains each possible cause in plain language, what you can safely check yourself, and when cold air means it's time to book a furnace repair.