Why Is My Furnace Blowing Cold Air?

February 23, 2016

Spring is getting closer, but there are a few days of winter weather clinging to the forecast in the upcoming weeks, which means your furnace needs to be fully functional. Have you noticed lately that your heater is blowing cold air out of the registers? If so, the following checklist may help you identify the problem; otherwise, give one of our technicians a call and we’ll come out within 24 hours to fix the problem!

Check the Thermostat

There could be a few different issues with the thermostat that could cause your furnace to blow cold air:

  1. The thermostat is set lower than the temperature in your home.
  2. The batteries in your thermostat could be dead or dying. (Some thermostats run on batteries only, without a backup.)
  3. The thermostat is set to ON instead of AUTO.

If you notice your furnace is blowing cold air only some of the time, but the blower is constantly running, then the problem could be number three listed above. With the thermostat set to ON, the fan will continue to run even when your furnace is not heating the air in your home. Switching the fan setting to AUTO will allow the furnace to blow only warm air.

Check the Filter

Clogged filters are not only inefficient for your furnace, but they can also cause them to overheat. Dirty filters block airflow, which means your furnace has to run longer to heat your home. If this is the cause of your furnace problem, your furnace will blow warm air, then cold air, and eventually stop blowing air all together. Most furnaces have a built-in safety feature that turns the burners off when the furnace gets overheated, but the blower will stay on to cool the furnace to a safe level. It is absolutely crucial that you address this problem right away by changing the filter. You may even want to change the filter whenever you are troubleshooting furnace problems because clogged filters are often the simple solution to many issues for your heating and cooling unit.

Check the Fuel Source

Whether you are running a gas, electric, or oil furnace in your home, make sure your unit is receiving its fuel supply. Gas valves must be open to allow the fuel to get to the burners; electric furnaces must be turned on at the breaker level and at the furnace’s ON/OFF switch; oil tanks must contain an appropriate amount of oil in order to effectively heat your home. If your furnace is not receiving its fuel supply for any reason, it will blow only cold air.

Check the Pilot Light

A gas furnace has a pilot light, a small flame that is always burning to help the furnace ignite more easily. The pilot light may be out, causing the furnace to blow cold air. Try relighting the pilot light; if it won’t light or won’t stay lit, there could be other components that need to be cleaned or replaced. Pilot lights can be a major fire hazard if they are not lit or fixed properly. If you are uncomfortable tending to the pilot light, call a professional heating and cooling contractor.

Check the Ductwork

Ductwork that is unhooked, broken, or installed improperly allows cold air to seep into the system. Your furnace may be feeding warm air into the ducts, but the air is cooled by the time it is blown out of the registers. Clogged ducts are extremely rare but may be worth checking into if you are unable to identify the cause of the cold air. If you suspect faulty or damaged ductwork is the source of cold air being distributed throughout your home, hire a professional to inspect the ductwork.

Remember, your safety and comfort is our number-one priority. If you have any questions or concerns about your heating system, please don’t hesitate to contact Lenz Heating & Cooling today.