My furnace is blowing cold air
Here in the Colorado Springs area, we often receive frantic calls from homeowners whose heating system has gone on the blink, and a typical call goes somewhat like this
Please help me! My furnace is blowing cold air. And is not keeping my house warm!
What causes a furnace to suddenly stop heating and just as suddenly start blowing out cold air? Well there are numerous posibilities, but the most common culprit is dirt! Thats right! Your furnace is dirty and its decided to punish you by only blowing out cold air since youve neglected to have it serviced and cleaned for several years. Joking aside, theres quite a ring of truth to this. Many of our service calls to repair a non functioning furnace is the result of neglect. That is, dirt, soot or oxidation of a key component in the furnace has resulted in the furnace not working properly, or not at all.
Ive seen motors completely fail due to excessive dirt buildup on and around the motor, or ignitors short out because of dust or lint buildup on the surface. Imagine having to fork out two, three, four hundred dollars or more to replace a failed part simply because routine maintenance has not been performed on the furnace as it should be (once a year is recommended).
Different brands of furnaces will respond differently when components fail or are in need of servicing. For example, almost all furnaces will stop heating and begin blowing cold air if the furnace filter(s) becomes too dirty or plugged. Why is this? Because a dirty or plugged filter will result in too little airflow across the furnaces heat exchanger, which will cause a temperature limit switch to fault (in order to prevent the furnace from overheating). When the furnace detects this fault, it will turn off the gas and keep the blower running in order to cool the furnace down.
Of course, certain parts can fail and depending on the model of the furnace, this too can activate the blower without the furnace heating. Another example is a stuck or failed pressure switch. On some model furnaces, nothing will happen other than the vent motor running continuosly. On some models however, this will also cause the main blower to just blow cold air until the problem is corrected.
Regardless of the cause, if your furnace is only blowing out cold air, or intermittently blows cold air while occasionally heating, then there is a problem that needs to be addressed by a qualified heating technician. Do not wait for the problem to fix itself. That isnt going to happen. When youre aware of a problem with your furnace, have it looked at as soon as possible. Delaying service may result in even more problems that couldve been prevented by quick action.