Why Is My Furnace Blowing Cold Air?

There are few things worse than trying to warm your hands near a heating vent only to feel a blast of cool air. Here’s a look at the most common reasons for this inconvenient scenario.

Dirty Air Filter

When the filter gets clogged, it restricts airflow, overheating the furnace and causing the safety feature to automatically shut off burners. If this is the cause of your trouble, a simple replacement should fix the issue.

Thermostat Malfunction

If a single vent blows cool air but the space heats to the desired temperature, it could be a faulty thermostat. The easiest way to fix the issue involves keeping the thermostat on the auto setting. When set to “on,” the fan blows continuously, even if the furnace isn’t heating the space.

Also, if you recently installed a new thermostat not compatible with the heating system, the furnace won’t function properly. A low thermostat battery could also be the problem. Whatever the issue, it might help to have a professional HVAC technician check it out.

Technical Issues

Newer systems have electric control panels that can periodically malfunction. Sometimes, restarting the system helps (like rebooting a computer). If not, you’ll need the expertise of a professional.

Low Gas Supply

When gas gets low (or the supply gets turned off), the furnace won’t heat sufficiently and will automatically shut itself off (for safety reasons).

Ignition/Pilot Light Issues

If the furnace doesn’t light the fuel like it should, it won’t heat your home and might feel like it’s blowing cool air. You can try relighting the pilot light (if you feel comfortable) or having a technician do the work.

Faulty Valve

If debris builds up inside the system, it can cause the gas valve to stick. Having a professional cleaning will help solve the problem.


Modern furnaces have condensate drain lines that remove moisture created when water heats. If the line becomes clogged, it can engage a dial that prevents burners from lighting.

Duct Problems

If cold air–from the attic or other crawlspaces–gets into ducts, it can affect warm air. To prevent this issue, have your trusted HVAC professionals check and repair all ductwork.

The fix for most of these issues is having your system cleaned regularly by a professional. When dirt and debris build up inside your furnace, it can cause premature wear and even failure.

For all your heating and air conditioning needs, call Vredevoogd at 844-HVAC-365.

Call Vredevoogd Heating & Cooling for all your plumbing, heating, & cooling needs. In the greater Grand Rapids, Kalamazoo, Lansing, Lakeshore, and surrounding areas call: 844-HVAC-365