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Why is My Furnace Blowing Cool Air in the Winter?

November 7th, 2018

Blowing Cold Air Vent

Winter means your furnace will be working harder than at any other time of the year.

Before snowstorms strike this season, you have the perfect opportunity to get furnace maintenance. One of the most common problems homeowners report with their furnace is cool or lukewarm air coming from the vents. Although it’s usually an easy fix, finding the root cause can be tough.

If you’re not getting the hot air you expect from your furnace, check for these issues:

1. Thermostat Troubles
Your thermostat serves as the brain of your furnace. It’s always the first thing any professional will check on when responding to a maintenance call. If your fan’s blower is set to ON, it will blow continuously. Switch it to AUTO to ensure that it only blows warm air.

2. Leaks in Ductwork
When ducts leak, your furnace will struggle to reach the temperature you want and you may notice high heating bills. Leaks mean that cold, unconditioned air will get sucked in and mixed with the air from your furnace. That makes the air output much cooler than it should be.

3. Pilot Light Not Working
The pilot light is a small gas burner that runs continuously to light a larger one as needed. If your pilot light is out, try relighting it. If that doesn’t work, double-check that the gas valve is on and consider cleaning the pilot light. Still not working? Time to call an expert.

4. Fan Limit Switch Malfunction
If your “heated” air blows cold, then warm, then cold again, the culprit may be the fan limit switch. It helps determine when the fan should be blowing in relation to the furnace temperature. Only a technician should attempt to adjust this switch.

5. Furnace Overheating
If the furnace experiences overheating, it will automatically shut off the burners. However, cool air will continue to blow from the unit. To resolve the issue, first try replacing your air filter. Most overheating issues are caused by restricted air flow as the filter becomes dirtier.

6. Inadequate Gas Supply
Modern furnaces are designed to lock down if gas supplied to the equipment is not sufficient for safe operation. Although this is a rare problem, it is also the biggest. If your gas supply is not turned off, then you might have a severed gas line in need of immediate attention.

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