Heating System Guides

Consumer Buying Guides to Home Heating and Air Conditioning Systems

Reasons Why Your Furnace is Blowing Cold Air

Cold air is the last thing you want to feel blowing from your forced air heating system vents, but it’s a reality many of us will face this winter. Whether you woke up to the gas furnace blowing cool air, or it just stopped working in the middle of the day, you probably want to figure out what went wrong quickly, so you can get warm heat in your home as soon as possible! Many times, gas furnace maintenance & cleaning can find small furnace problems before they turn into bigger issues, so make sure you have your system checked at least once a year.

In this Home Heating System guide, we’ll take a look at the various reasons why a furnace blows cold air, when it should be blowing warm and heating your house properly! We’ll also share several of the things you can check on your own, and when you need to call in a heating contractor before you jump in over your head.

Start with the Obvious Reasons for No Heat

When you begin looking for the reasons for cold air, start with the most obvious, it’s usually the easiest way to troubleshoot the no heat problem. Once you exhaust the ways a homeowner can troubleshoot a furnace, then you can call in a pro (get free repair estimates) to take over and look at the more technical reasons.

In order to create heat, you must have fuel. The first thing we’ll check is the availability of fuel like natural gas, heating oil or electricity:

  • Gas Furnaces, do you have natural gas or propane? Is it on? Do other gas appliances work?
  • Oil Furnaces, do you have oil in your tank? If it’s low, it may be contaminated with water. Is the oil filter clean?
  • Electric Furnaces, does the power work to other electric appliances? Is the circuit breaker to the unit tripped?

After you’re sure there is a fuel source to the furnace, you can check these common reasons a furnace isn’t working right:

  • Is the Circuit Panel Tripped, or Power Out to Unit? Even gas and oil furnaces need electricity to work. Check your circuit panel for tripped breakers or blown fuses.
  • Is the Thermostat turned to Heat Mode? This is the most common reason a  furnace blows cold air, it’s till in cooling mode. Also, don’t forget to check the individual room thermostats for zoned hvac systems.
  • Are the Return Air Filters Clean? – A dirty hvac filter can trip a limit safety feature, and shut down automatically before the burners ignite.
  • Is the Furnace Pilot Light Lit? Older furnace (+15 years old) use a standing pilot light to ignite the burners. If your old gas or oil furnace uses a standing pilot system, the light must be lit to ignite the fuel.
  • Is the Furnace Door Properly Attached? – Although the front cover on most gas and oil furnaces is removable, it’s also got to be re-attached tightly in order to light. Make sure the door is properly fastened to the unit.

Now for the More Technical Reasons its Blowing Cold Air

After you check the things a homeowner can do on their own, it’s probably the right time for you to call in a heating repair contractor to have a look at your furnace, and get it repaired. (Click here for free repair estimates from local contractors) All furnaces have a specific sequence they cycle through, to start up and then produce heat. Aside from variables for the various types, a furnace start-up sequence goes like this:

  1. Thermostat Calls for Heat and Tells Furnace to Light
  2. Draft Inducer Spins Up and Prepares the Unit to Light
  3. Safety Checks Are Performed to Make Sure the Furnace is Safe to Light
  4. Pilot, Ignitor, or Thermocoupler Energizes to Set Temperature and Awaits Fuel to Ignite (Ignitor is Most Common Furnace Part Failure)
  5. Safety Checks are Performed to Be Sure Ignitor is Ready to Light Fuel
  6. Gas Valve Opens (or oil fuel pump) and sends Fuel to System, Igniting and Burning into the Heat Exchanger
  7. Safety Sensors Monitor Temps of Burner and Flue to Be Sure Venting Occurs Properly
  8. After a Set Time Delay, the Blower Starts and Sends Heated Air Across Heat Exchanger, and into Home
  9. When Thermostat Set-point is Reached, Furnace Cycles Off

Of course there is a bit more to it than outlined above, but the general procedure is the same. Unfortunately, most of the things on the second list require you to call in a professional who has the right tools, training and experience with different types of furnaces to repair the furnace.

Has Your Furnace Recently Blown Cold Air?

If so, share what your technician or furnace repairman found and had to fix on your system. If it was a simple repair you did yourself, please indicate that as well.

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