The answer to 'furnace short cycling' is that your furnace is turning on and off rapidly, cycling through multiple heating cycles in a short period of time. This is a common problem that can be caused by a variety of issues, from a dirty air filter to a malfunctioning thermostat. Short cycling can lead to increased energy bills, uneven heating, and potential damage to your furnace if not addressed.
Some common causes of furnace short cycling include a clogged air filter, a problem with the thermostat, issues with the blower motor or fan, a cracked heat exchanger, or a problem with the furnace's control board. Symptoms may include frequent on/off cycles, uneven heating, and higher-than-normal energy bills.