If your furnace isn’t producing warm air as expected, don’t panic. The issue could be something simple, like a thermostat setting, or a more serious problem like duct leaks or a failing component. Before assuming you need a costly repair or replacement, here are some common reasons your furnace might be blowing lukewarm air—and what you can do about it.
1. Incorrect Thermostat Settings
One of the most common causes of lukewarm air is an improperly set thermostat. If your thermostat is set to "ON" instead of "AUTO," the fan will run continuously, even when the furnace isn’t actively heating. This can make it feel like your system is only producing lukewarm air.
Solution: Set your thermostat to "AUTO" so the fan only runs during heating cycles. If your thermostat is outdated or malfunctioning, upgrading to a programmable thermostat can help improve performance and efficiency.
2. Your Home Has a Heat Pump
Unlike a gas furnace, a heat pump moves heat from the outside air into your home. In colder temperatures, this process can result in air that feels less warm than what a traditional furnace produces.
Solution: If your heat pump isn’t providing enough warmth, check the outdoor unit for ice buildup and ensure it's in defrost mode. On especially cold days, using auxiliary heat may help.
3. Airflow Issues from Dirty or Improperly Installed Filters
A clogged or incorrectly installed air filter can restrict airflow, making your furnace work harder and reducing its ability to heat your home effectively.
Solution: Check and replace your air filter every 1–3 months. If airflow issues persist, professional HVAC maintenance can identify whether ductwork problems or other blockages are to blame.
4. Two-Stage Furnace Running in Low Mode
If you have a high-efficiency, two-stage furnace, it may run at a lower heating capacity to save energy during mild weather. This can sometimes make the air feel cooler than expected.
Solution: Adjust your thermostat to a higher setting if needed. If your home isn’t heating properly, an HVAC technician can assess whether your system is operating efficiently.
5. Leaky Ducts Letting in Cold Air
If your ductwork has leaks or gaps, heated air can escape before reaching your living space. This not only makes your furnace seem ineffective but also wastes energy.
Solution: Have your duct system inspected and sealed to prevent heat loss and improve airflow. Proper duct sealing can make a significant difference in comfort and efficiency.
6. Insufficient Gas Supply or a Faulty Flame Sensor
A weak gas supply can prevent your furnace from producing enough heat. Similarly, a malfunctioning flame sensor may cause the burners to shut off too soon, limiting heat output.
Solution: Ensure your gas valve is fully open and that your supply is consistent. If the furnace turns on but quickly shuts off, a professional may need to clean or replace the flame sensor.
Need HVAC Service in Lawton, OK? Contact Us Today!
If your furnace is blowing lukewarm air and you’re unsure why, Pippin Brothers can help. We provide expert furnace repair, duct sealing, thermostat upgrades, and airflow balancing to restore comfort to your home.