Your furnace blows hot air but that air quickly turns cold then the furnace shuts off altogether. If everything seems to work properly, and then your furnace blows cold air back and forth until it switches off, you may be faced with a furnace that has overheated. This can cause your furnace to lock down for safety. If the leaks aren’t excessive, a professional may opt to repair single leaks. If your furnace seems to be blowing cold air, it could be a problem with the ignition system. First – make it worse. If your furnace is blowing cold air, we’re sorry! If your furnace fan is set to ON, the fan runs continuously, whether or not your furnace is producing heat. 2. This could happen from a gust of air caused by someone working near the furnace. Check that all supply vents are open. Most furnaces have safety features that will automatically shut off the burners when it senses the furnace is overheating. If your furnace continues to blow cold air then you should check if you have a two-stage furnace. If you know how and you’re comfortable doing it, you can try to relight the pilot yourself. When this happens, your … Even worse, the furnace is blowing cold air! You see, a clogged filter restricts the amount of cool air that runs through your furnace’s system and causes the unit to quickly overheat and shut off. If you have a newer furnace with an electronic ignition, such as an intermittent pilot or a hot surface ignition, your system may need adjustments or replacement of failed parts. Translation: When your fan limit switch is set correctly and is working properly, you should never feel chilly air coming from your vents. That may be a quick and easy fix. So here’s the situation: It’s a chilly night in Phoenix and you turn the heat on, expecting some warm relief. Turn off power to the furnace at its ON/OFF switch. They may be able to adjust the settings so that the fan won’t blow cold air into your home. Learn more from our free guide: HVAC Preventative Maintenance Contracts: How to Find the Right One for Your HVAC Infrastructure. Do you have thermostat wars going on in your office? Why Is My Furnace Blowing Cold Air? You’ll need a visit from an HVAC professional to make this furnace repair. The best service providers can customize a plan for your needs and your budget. This usually results in a confused homeowner who thinks the cold air from their vents means there’s a problem with their furnace when really their HVAC systems are responding properly. Again using Occam’s Razor, we can assume that the next likely culprit for your heater blowing cold air is your thermostat. How Does Workplace Ventilation Impact Employee Productivity? Change the setting back to AUTO, and you’ll have heat again. If the furnace burner itself is neglected, accumulated dust and grime can cause trouble igniting. Heat Pump Troubleshooting: 3 Common Problems and Solutions, The Rewards of Giving Back: Arista Team Rebuilds a Home in Puerto Rico, Commercial Refrigeration Service & Repair. Have your system professionally cleaned to take care of this problem. But, if the switch is bad, they’ll need to replace it. 6. If your furnace is blowing cold air, check your thermostat, air filter and ductwork. Make sure your thermostat is set to HEAT and your fan is set to AUTO. Read on to learn the 13 most common reasons for your furnace blowing cold air and when to call for a furnace repair. December 16, 2020. If yes, our team in Conway, SC, suggest checking a few things first and then call us for help. If gas supply is interrupted for any reason, the gas furnace pilot light will go out. If the filter becomes clogged, the unit can start to overheat and cause the burner to shut down. A furnace that isn’t getting fuel will not ignite and will blow only cold air. So, how do you know which problem is causing your furnace to blow cool air? You may also see an error message on your thermostat, or a blinking LED light on the furnace control board. Check the furnace’s air filter. If your furnace is blowing cold air, or is not operating at all, a component called the fan limit switch may have malfunctioned. Do you have thermostat wars going on in your office? Is your furnace not blowing hot air? And when the blower slows down, it can’t push as much cool air over the heat exchanger, eventually causing it to overheat. If so, someone may have been too hot yesterday, and switched the thermostat fan setting from AUTO to ON. If you have a gas furnace, a lack of fuel will cause the pilot light to go out. This problem requires a visit from your HVAC repair technician. Pilot Light. Need a tech ASAP? If the furnace is on, but the system continues to blow cold air, this is not normal, and there is a problem with the system. To troubleshoot a misbehaving gas furnace, start with the easiest explanations and solutions, then work your way to the most complicated. This extra pressure puts strain on the furnace blower, slowing it down. Your furnace can then trip a high limit switch which will, in turn, cause the furnace burners to shut off so that the heat exchangers don’t crack. 13 reasons your furnace is blowing cold air 1. Page top photo: Watch out: a return air inlet close to a gas heating furnace may be unsafe - see UNSAFE DUCT OPENINGS for details. The thermocouple is a sensor that controls the gas valve and ignition. When overheating, your furnace can trip a high limit switch, causing the furnace burners to shut off so that the heat exchanger does not crack. This can be caused by something as simple as a strong draft. HVAC Preventative Maintenance Contracts: How to Find the Right One for Your HVAC Infrastructure. Check your air filter. Other thermostat issues. What Can I Do If My Heater Is Blowing Cold Air? You Own a High-Energy, Two-Stage Furnace. Wait a few minutes, then flip the switch to ON. It’s common for a furnace to blow cold air when you turn it on for the first time each season, but it can also happen at any time if something goes wrong. So, once a heating cycle ends and the furnace burners cut off, the fan continues to blow. Naturally, all heaters use a fan to blow air, but if your fan setting is set to ‘on’ throughout the day, it explains why the heater seems like it has malfunctioned. And because your furnace is no longer heating, the air being pushed into your home will be cold. No matter how you travel to work, whether it’s by bus, car or train, your commute probably ends with a cold walk in the icy wind. Ensure that your thermostat is set higher than the temperature in your home. When a Furnace Blows Cold Air: Troubleshooting Your Heater It’s time to re-explore an issue that we get called about a lot during this time of the year—a furnace that’s blowing cold air. A furnace that blows cold air could also indicate that it is overheating. If you only feel your furnace blowing cold air briefly, and the air is quickly replaced by warm air, this is the most likely explanation. This is usually a simple fix, but you’ll need to call a technician to adjust or replace it. Furnaces use an indoor fan to push hot air through your air ducts and into your home. The lukewarm air coming out of your furnace can also be the result of leaky air ducts. This too can cause your heater to blow cold air. If this doesn’t fix your problem, and your furnace is still not blowing hot air, you can move on to some of the other potential culprits. Major duct problems. A dirty air filter blocks airflow over the furnace’s heat exchanger, causing it to overheat. Your furnace’s limit switch, which specifically works as a safety measure, has turned your furnace burners off until the unit reaches a safe temperature. If you have an oil-fired furnace, you may be out of fuel. IAQ and Mold in NYC Buildings: Are Kids at Risk. If you know how, you can clean or replace the filter yourself, but it’s messy and not as easy as an air filter so you may want to leave this job to the pros. When a furnace blows cold air, there may be an issue with the unit’s electronic control panel. Wait a few minutes, then restart. If your furnace is blowing cold air, not blowing any air at all, or making odd noises, it’s important to schedule a repair as soon as possible. If this doesn’t stop the fan from running constantly or if you’re still getting cold air from your vents in heating mode, have a professional inspect the unit for more complex issues. Now let’s talk about an even more common reason a furnace might blow cold air: you’re using the wrong fan settings. So, how do you know which problem is causing your furnace to blow cool air? If you did it yourself instead of calling a professional, you may have chosen a thermostat that’s not compatible with your heating system. It is usual for cold air to enter the heating system until it is warm, and then for warm air to continue to blow after the air heats up. This is sometimes easily solved by resetting the system. When the fan is on, the furnace will continue to blow, regardless of whether or not the air is being heated. Furnace Blowing Cold Air? What’s wrong? Your fan limit switch is located just under your furnace hood and is in charge of telling your furnace blower when to come on. This can cause the air to … Your furnace may be blowing cold air because the filter is too dirty. You also don’t want to risk frozen pipes. When the chilly weather finally arrives, and you have to turn on your furnace for the first time after many months of non-use, the last thing you want to find is that it’s not working. Instead, you’re blasted with cold air. You’ve got three basic options. Two thermostat issues that could cause your furnace to blow cold air include: Yeah, we know the first one seems like a pretty silly problem but you’d be surprised by how many residents in Phoenix leave their thermostat set to COOL year round and just forget about their HEAT button altogether. All Rights Reserved. Ductwork with a loose connection. In such cases, a safety control device known as the limit switch will shut off the burners. Go to your thermostat. 1. If you have a newer furnace with an electronic control panel, you may need to reset the system. If the filter looks like the filter to the right in the picture below, replace it. Well, it could be multiple issues; some of them you can solve yourself. Even if your furnace is fairly new, things can go wrong that cause this unpleasant surprise. Here in the New York City area, we’re all pretty tired of the cold weather by now. Have your system cleaned and checked by an HVAC professional. If not, the compromised air flow can cause your furnace to overheat, shutting down the burner. Why Is My Furnace Blowing Cold Air? There are several possible causes for a furnace blowing cold air, so it’s hard to give you advice without more information. This usually arises if you haven’t changed your air filter routinely. The fan setting on your thermostat has two options, “on” and “auto”. If your issue continues, call our team in Tacoma, WA. Basically, the furnace isn’t lighting the fuel, meaning it can’t heat your home, either. If you do manage to relight the pilot but it keeps going out, a faulty thermocouple is likely causing your furnace to blow cold air. The furnace is blowing cold air. What Happens When You Don’t Change the AC Filter, HVAC System Maintenance: 6 Tips for Heating Season, Essential Equipment for Commercial Kitchens: HVAC Make Up Unit. Large holes and leaks in air ducts can make it seem like your furnace … This means the fan will run continuously without providing heat. Meanwhile, you’ll get cold air because the fan continues to run as a safety measure, even after the furnace isn’t producing heat. ... Start by taking a look at the limit switch. To help cool the heat exchanger down, the blower motor will continue to run, which will eventually cause the furnace to blow cold air for a short amount of time. If you’re still not getting warm air from your furnace, we can help. Consult an HVAC expert for advice. Count your blessings that this time you avoided an expensive furnace repair. The stat is reading at 19 but I have it set - Answered by a verified HVAC Technician. If not, call a professional. If the pilot won’t light at all, you may have a faulty gas valve. Common Ignition Problems. But you need to know when to call in the furnace repair pros so you don’t have to spend unnecessary time in the cold and interrupt your business. Unfortunately, you’ll need a professional to fix this problem. The furnace says it’s a thermostat issue. When the filter is clogged, ignition can be affected and the result is your heating not blowing hot air. Clogged air filters could be causing cold air to blow out of your vents. Have you installed a new thermostat lately? So what’s the problem? Have an expert inspect your ducts along with the furnace. Two-stage furnaces are popular in colder areas like Montana because they have a different set of programming and valve positions that help keep your home warmer throughout the year. In some cases, you may be able to fix the problem yourself. If your furnace overheats, it could end up blowing cold air. If so, your blower may keep circulating cold air even after the burners fail to light and produce heat. Or the gas line isn’t supplying enough gas to your furnace. If you don’t know what a pilot light is, it’s a small flame that runs at all times in order to light the burners in your furnace. However, the fan will keep running, cooling the furnace to protect it from potential damage. 3. If your forced-air gas furnace is blowing cold air, a number of factors could be to blame—many of which you can address on your own, without the immediate help of a service professional. © 2021 Patrick Riley, LLC. See our response to recent issues regarding COVID-19. This is of course a very unsettling problem and not one that you want to face. If your furnace starts blowing warm but then quickly turns cold, the flame sensor may need attention. COVID-19 & Your HVAC System: Your Questions Answered. Your supply vents (pictured below) push warm air into your home. Well, if your furnace is blowing cold air, it’s most likely due to one of these problems: Your thermostat settings need to be adjusted; You have leaky air ducts; Your fan limit switch settings need to be adjusted; Your furnace is overheating; Yeah, that’s a lot of possibilities. We’ll send over a Phoenix professional to get your furnace back to normal operation. Try changing the air filter and restarting the furnace. 2. That’s why the furnace is not blowing hot air. If you haven’t done that yet this winter, call in an HVAC service expert to keep your system in top shape and prevent unexpected failures. If you have an oil-fired furnace, its filter can become clogged with dirt and debris, just like an air filter on a gas-fired system. Inadequate gas supply. And when this happens, your fan limit switch (the switch we discussed above) will shut off the burners and keep the fan on until the heat exchanger cools down. If so, someone may have been too... 2. 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