My furnace ductwork is getting between 200 and 230 degrees Fahrenheit and the vents are around 111 degrees. What would be the cause?
The furnace should have a name plate or sticker (possibly inside) that indicates the maximum outlet air temperature as well as the expected temperature rise (typically 40-70F). 110F out of the vents themselves certainly sounds high to me.
If air temperature coming out of your furnace exceeds the upper limit of temperature rise given on the heater's data tag, it needs repair. A too-hot furnace heat exchanger can be damaged, might crack, and could leak dangerous combustion gases or carbon monoxide. This might result in a house full of dazed, disoriented, or dead people.
Have you checked the filter? Are you trying to shut off the heat to parts of the house? The necessary repair might be as simple as replacing the filter and making sure vents are open. If the filter incredibly clogged it could be causing too low of air flow, resulting in a high discharge temperature from your furnace. Check the filter, check to make sure return air vents are clear, check to make sure that supply vents are not all shut down with the dampers.
If you have to use the system right now because of the cold snap, be certain your carbon monoxide detectors are working. In fact, make sure they are working no matter what, as they're a critical part of furnace safety.
Once you've checked and eliminated the items above and validated against your furnace data plate, if you're still out of range on temperature it's time to schedule service for your furnace.
I had the belt on a furnace blower break. It sounded like the furnace was working per normal but the motor wasn't driving the fan without the belt.
The result was that the furnace would run constantly as the air wasn't getting to the thermostat efficiently. It would heat the house but just via convection. Since the furnace was on all the time the metal vent components all were very hot to the touch.
Your furnace should have a bonnet control which generally has an over temperature sensor in it as well. Many of these are adjustable. This will limit the temperature output of the furnace. If the safety trips it will shut it down. The burner puts out a constant amount of heat, it is the responsibility of the blower to move enough air to keep it within operating range. Restricting this will cause problems similar to what you have. Simply remove the filters and see what happens. If that solves it your filter is to fine or very dirty. Some older furnaces had adjustable blower speed control, some with the motor others had a variable speed sheave on the motor. Good Luck. Hint when kids go to school in the fall have the furnace checked.