The answer to 'furnace blowing hot air' is that your furnace may have a problem that is causing it to blow hot air even when it should be cycling off. Some common causes include a malfunctioning thermostat, a clogged air filter, a problem with the furnace's control board, or an issue with the furnace's heating element or burner.
If your furnace is blowing hot air when it should be cycling off, the first thing to check is the thermostat. Make sure it is set to the correct temperature and that it is functioning properly. You can try adjusting the thermostat or replacing the batteries if it has them. If the thermostat seems to be working correctly, the next step is to check the air filter. A clogged or dirty air filter can restrict airflow and cause the furnace to overheat. Replace the air filter if it is dirty.