What can be more frustrating than a heater blowing cold air when you need hot air the most? It could be that your furnace blows warm air sometimes and cold air most of the time. Or the furnace always blows cold air. Before you troubleshoot the problem, it is important to understand how the furnace is blowing cold air. Let’s see what causes both the scenarios and how to fix it:

Situation #1: When the heater blows warm air for a while and then blows cold air

There could be two possible causes for this:

  1. The thermostat fan is set to “ON”

The fan in the furnace is responsible for blowing heated air through the vents. If it is set to “ON”, it will continue blowing air even if the furnace is not heated. This makes it feels as if the furnace is blowing cold air even though it is only blowing room temperature air.

If you experience this, then check the thermostat. The temperature of your home must reach the set temperature. If it has already, then switch the fan’s setting to “AUTO.” This will solve the problem and your fan will start blowing only when the furnace is heating.

  • The furnace is overheating

If it’s not the problem mentioned above, then chances are your furnace is overheating. When this happens, the safety switch automatically turns off the burner and slows the fan to continue blowing cold air. Once the heat exchange cools down, the furnace restarts and throws heat. When it overheats, the cycle continues.

To fix this, change the air filter. Usually, furnaces overheat because of dirty air filters. It restricts the airflow coming into the furnace which makes it hard to work properly, hence the overheating.

If you have changed the air filter and the problem persists, you should contact a heating repair company.

Situation #2: The furnace always blows cold air

This one’s a little difficult to troubleshoot but here are the possible causes:

  1. The thermostat isn’t set to “HEAT”

We often don’t check the thermostat, especially programmable ones. We set it once and forget about it; however, some thermostats may have multiple options: AC only, heat only, or a combo – where the HVAC system automatically switches between heating and cooling to maintain the desired temperatures. It may seem like too simple of a mistake to make, but trust us, if we are mentioning it, it is because we have come across it. Look at your thermostat before rushing to call a heating repair company and make sure it is set to “HEAT” and the fan is on “AUTO.”

  • The burner is not lighting

This happens when you have a gas furnace. It could be blowing cold air because the burner hasn’t ignited. It is possible the igniter isn’t functional to begin with or the gas supply is insufficient.  It could also happen because of a clogged condensate drain keeping the burner from lighting. With this, there are few trouble shooting options:

  • Depending on your furnace set up, check to see if you can see the burner – is it lit?
  • Are you supplying the propane or the utility company? If you supply your own, it may be possible your gas supply is too low for the burner to ignite. If a utility company supplies your gas, you can contact them to inspect the flow of propane to your home.
  • Check the condensate drain – does it appear to be functioning normal (slow drips) or is the drain pan or outdoor area dry? Try cleaning your condensate drain pipe if you think this may be the culprit.
  • When all else fails, contact a heating repair company to inspect your furnace and get your heat back up and running.
  • The duct is leaking

If there are leaks and holes in the air duct, it could suck cold air from the crawlspace and blow it into your house. Some leaks may be able to be repaired yourself with the right materials and if the leak or tear in the duct is easily accessible. If you can repair the issue without causing further harm to the duct system, it will save you a visit from a HVAC technician.

Conclusion

Your heater could be blowing cold air for all sorts of reasons. Even though you can look for possible causes, for proper diagnosis, it is best to call a professional heat repairing company. At some point, it’s more affordable to reach out to the pros. Make sure you hire a licensed HVAC contractor for troubleshooting and fixing the heater.