Why Is My Furnace Blowing Cold Air?
When the cold winter weather settles in, having a reliable furnace is a must to keep your home and family warm. However, all furnaces are prone to malfunctioning at one point or another. One problem you may experience is your furnace blowing cold air. Below, we’ll address why this may be and what you can do about it.
What Does It Mean When Your Furnace Blows Cold Air?
When your furnace blows cold air, it could be the result of one of a number of problems. It’s important to keep in mind that there are two main components of your furnace. There’s the furnace itself that works to produce heat, and the blower compartment that circulates air throughout your furnace and ducting. A malfunction in just one component can cause cold air to come out of your vents.
13 Common Reasons Your Furnace Blows Cold Air
When your furnace starts blowing cold air, it’s likely you want to solve the issue as quickly as possible. By understanding the root causes of this malfunction, you may be able to fix the issue on your own. However, in more severe cases, you may need to call our professionals for prompt assistance.
1. Thermostat Set to Cool or Fan Set to On
One of the most overlooked reasons that your heater may be blowing cold air is that your thermostat is set incorrectly. It could be that your thermostat is set to cool instead of heat, which means you just need to switch it over to heat mode. It could be that you have your blower fan set to ON instead of Auto.
When the blower fan is set to auto, it only turns on whenever your heating system turns on. However, if the blower fan is set to ON, it will run 24/7. This means it will disperse hot air when your heating system is running, but circulate unheated air when your heating system is off. This is another easy fix. All you need to do is switch your blower fan from ON to AUTO.
2. Dirty or Clogged Air Filter
Another often overlooked cause of why your furnace may be blowing cold air is a dirty filter. Whenever your filter is full of debris, it makes it much harder for your heating system to force air through it. Without adequate air movement through your furnace, it will overheat.
All modern furnaces have a built-in limit switch that automatically shuts the furnace off when the temperature gets too high. This could leave your blower fan running, circulating unheated air since your furnace is off. All you need to do to fix this issue is replace the dirty filter with a new one.
3. Closed or Blocked Supply and Return Vents
Any time that your vents or registers get blocked, airflow is restricted. Unfortunately, if there’s too much restriction in the airflow through your ducting, it can cause your furnace to overheat, as it automatically shuts off as part of its safety procedure. It’s best to remove any obstructions that are blocking your vents or registers to ensure adequate airflow throughout your entire ducting system.
4. Pilot Light Has Gone Out
If you have a furnace that still relies on a pilot light, that light needs to stay lit 24/7. Whenever the pilot light accidentally blows out, it won’t be able to light your burner. So, your furnace cannot burn fuel to create heat. If your pilot light is out, the blower motor will still circulate air throughout your ducting that’s unheated. It can be helpful to follow the procedures in your manufacturer’s pamphlet about your furnace to relight your pilot light.
5. Faulty Electronic Igniter
Similar to a pilot light, all modern furnaces have electric igniters. If the igniter isn’t functioning to send a spark to ignite the burner, your furnace can’t burn fuel to create heat. The blower fan will still run and circulate lukewarm air throughout your home. If you have a faulty igniter, you’ll need one of our professional technicians to replace it for you.
6. Clogged Condensate Drain Line
High-efficiency furnaces produce moisture that must be drained through a condensate line. Any time that line gets blocked full of debris, water can’t leave the furnace. Your unit will automatically shut off as a safety mechanism. This is another scenario where you’ll be left with a blower circulating unheated air throughout your home. Contact one of our professionals to unclog your condensate line for you.
7. Gas Supply Valve Turned Off or Restricted
For your furnace to produce heat, it needs a steady supply of fuel. If, for some reason, your gas valve got turned off or is obstructed by debris, your furnace can’t get the fuel it needs to create heat. This will result in a blower fan circulating unheated air. You can check the gas valve and turn it back on if it was shut off. If that doesn’t solve the problem, you’ll need one of our technicians to further assess what’s restricting the flow of gas to your unit.
8. Dirty or Failing Flame Sensor
Gas furnaces have a safety mechanism known as a flame sensor. Its job is to detect when there’s a flame on the burner and shut off the gas supply valve if there is no flame. This is necessary to prevent gas from building up inside the combustion chamber. Unfortunately, if the flame sensor eye is dirty or the unit itself is faulty, it may trip the safety mechanism that stops the supply of fuel to your furnace.
This can leave your blower fan circulating unheated air throughout your home. You can try wiping the sensor eye to see if you can restore functionality to the sensor. If that doesn’t work, one of our technicians will need to replace the faulty flame sensor.
9. Tripped or Faulty High Limit Switch
The high limit switch for your furnace is specifically designed to shut it off in the event of overheating. This helps to minimize your risk of experiencing a fire with the unit. If the limit switch itself is faulty, it will prevent your furnace from turning on and simply allow the blower fan to circulate unheated air.
10. Furnace Overheating From Poor Airflow
If there is inadequate airflow in your furnace, it will overheat and automatically shut down. Inadequate airflow can be caused by numerous things, such as a dirty air filter, obstructions in your ducting, or other issues. It’s necessary to get to the root cause of the restricted airflow and remove it to restore functionality to your furnace.
11. Leaky or Poorly Insulated Ductwork
Anywhere that there’s a leak in your ductwork, the hot air your heating system produces can escape. By the time the air reaches certain rooms in your home, it may feel cold. In this scenario, it’s best to invest in duct sealing service to get rid of those unwanted leaks.
12. Oversized System That Short Cycles
If you recently had your furnace replaced and are experiencing this issue, it’s likely that you have an inappropriately sized furnace. When the furnace is oversized for the space, it will short cycle, meaning it won’t run through an entire heating cycle. You may feel an abundance of cold air following the heat after your unit shuts off. Getting an appropriately sized system is necessary to fix this problem.
13. Aging Furnace or Failing Heat Exchanger
If the heat exchanger on your furnace is compromised, it can allow your hot air to escape instead of making it to your rooms. Furthermore, if you have an aging furnace, it can have inefficient operation that won’t produce sufficient hot air for your home. Upgrading to a new furnace is the best way to solve this issue.
How Do You Fix a Furnace That Blows Cold Air?
For airflow issues, you can ensure all your vents are open and replace your furnace filter if it’s dirty. You can check your thermostat to ensure that it’s set correctly or make the necessary adjustments. If your pilot light went out, you can relight it. Beyond that, it’s necessary to have one of our professionals determine the root cause of the issue and repair it.
Is It Safe to Run a Furnace Blowing Cold Air?
It’s typically best to shut your unit off and determine why it’s blowing cold air. In some instances, continuing to run your heating system could cause permanent damage. It’s best to get a professional evaluation before turning your heater back on.
When to Call a Professional Furnace Repair Tech in Killeen
Deane Electric is your go-to expert for prompt furnace repair. Anytime that your furnace is blowing cold air and the simple troubleshooting solutions above don’t fix it, you need professional help. We offer 24/7 emergency repair services for all our customers. Simply give us a call today to get the expert help you need.