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(707) 539-4533 |  Sonoma Napa and Marin Counties

updated 11/16/22


At this point, you may have had an HVAC system for long enough to think that you are familiar with every component you need to know. However, both air conditioners and furnaces are usually more complicated than people think—that’s why it takes so long to become a licensed HVAC technician! As such, there are probably several parts of your furnace that you don’t fully understand (in fact, you may not even know that some of them exist yet). If, for instance, you’ve been wondering what a furnace evaporator coil is or why it’s important, read on, pay attention, and learn all you need to know about this often-overlooked but critically important part of your furnace.


HVAC 101 Everything you need to know


What Does a Furnace Evaporator Coil Actually Do?


Furnace Evaporator CoilThe furnace evaporator coil plays one of the most critical roles in an HVAC system. It can sometimes be found inside your air handler but is commonly located within the furnace itself. The evaporator coils job is to help the refrigerant in the HVAC absorb heat from the surrounding air. In most cases, the evaporator coil will work with both your air conditioner and your furnace, depending on which system you are using at any given time.


When your evaporator coil is functioning as part of a cooling system, its job is to remove heat from the air inside your home. Your air conditioner will blow this warm air over the coil, after which the refrigerant will absorb the heat and lower the temperature of the air flowing across it. The indoor air is then recirculated throughout your system of ducts, providing a cooler temperature inside. However, when you run your furnace, the evaporator coil does not remove heat from the air blowing across it. Instead, the heated air must flow across the evaporator coil and through the same channels it uses to circulate treated air throughout your home.


Now that you understand what an evaporator coil does, it is essential to know what can go wrong with it so that you can avoid issues. The evaporator coil is one of the most critical parts of your air conditioning system, but a neglected coil can do more than impair your system’s ability to lower the air temperature in your home. In fact, a badly-maintained evaporator coil can also have a serious impact on the furnace’s ability to heat the air in your home efficiently.


Your Evaporator Coil is a Vital Part of Your HVAC System


The evaporator coil is an important part of any HVAC system. It’s actually connected to the air conditioner, not the furnace, and its purpose is to hold the refrigerant that cools the air passing across it. The air conditioner blows air from your house across the evaporator coil, the refrigerant absorbs the heat, and then the newly-cooled air is blown back out into the ducts. If the evaporator coil stops working, then the air conditioner won’t be able to cool the air, so it’s a vital part and can be expensive if you need to replace it.


So what does this have to do with the furnace? Generally not all that much, except for placement. In most HVAC systems, the furnace and the air conditioner will use the same access point to the ductwork. That means warm air generated by the furnace has to pass across the evaporator coil before it reaches the ducts and the rest of your house. Of course, the furnace and air conditioner won’t be working at the same time, so the coil won’t absorb any of the heat from the warm air. However, a dirty or damaged evaporator coil can still cause problems with airflow through the whole system, and that can affect the furnace as well. That means some problems with your furnace might not be coming from the furnace at all.


The evaporator coil can start to affect the furnace if it gets too dirty. If dirt and other gunk start to build up on the evaporator, it can block airflow coming from both the air conditioner and the furnace, which can cause some serious problems for you and your furnace. The most obvious problem is that the warm air won’t be able to get to the ducts and the house will be colder than it’s supposed to be. If you notice that your furnace doesn’t seem as effective as it usually is, a dirty evaporator could be the culprit.


More importantly, the warm air that’s supposed to be reaching your house can end up getting caught in the ducts. This can be a problem in a few different ways. The first is that the warm air surrounding the furnace can confuse the sensors and make them think the house is warmer than it really is, causing the furnace to short-cycle, or switch on and off rapidly. If too much warm air builds up in the ducts and the area surrounding the furnace, it can also become a fire hazard. It’s easy for a furnace to accidentally overheat if it’s not running smoothly, and the presence of gas inside the unit can make that a dangerous proposition. It’s important to keep up with your regular yearly service appointments for your HVAC system so a dirty evaporator doesn’t end up blocking airflow through the whole system.


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Possible Consequences of Neglecting Your Furnace Evaporator Coil


How can a poorly-maintained evaporator coil affect a furnace if its only function is to help your air conditioner cool the air in your home? The key lies in the evaporator coils placement within the HVAC system. Remember earlier, when we said that the system had to blow air across the evaporator coil regardless of whether you were using the furnace or the air conditioner? Well, a dirty evaporator coil can make that difficult. In fact, when enough filth accumulates on an evaporator coil, it can obstruct the airflow in the system entirely, causing numerous problems. Poor airflow can result in:


  • A lack of warm air reaching the rooms of your home – leaving the occupants chilled when they need heat most.
  • Short-cycling of the furnace – When warm air becomes trapped in the ducts instead of being able to move into the home, it can confuse the furnace sensor’s interaction with the thermostat. As a result, the furnace can “think” that it has heated your home adequately, and then turn off abruptly. As soon as the air in the ducts cools off, the furnace will turn on again, and the process will repeat itself. As a result, your furnace will be unable to warm your home, and its components may wear out faster than usual, requiring expensive repairs.
  • Safety problems – Most furnaces have an automatic safety switch that will trigger if the temperature inside the system becomes too hot. However, if the furnace’s switch is not working correctly then the overheating that backed up ducts can cause may become unsafe, and even turn into a fire hazard.

Take Care of Your Furnace Evaporator Coil, and It Will Take Care of You


Dirty evaporator coils can lead to any of the problems listed above, so it is vital that you learn how to check your coils and have them cleaned on a regular basis. Be sure to contact professionals who have the necessary experience and qualifications, so that you can have confidence in the coils’ ability to function at all times. Investing in regular service for your HVAC and adhering to a schedule of preventative maintenance will prevent the coils from becoming dirty, and allow you to operate your furnace or air conditioner in peace.


Call Valley Comfort Heating & Air Today


If you experience any of the problems mentioned in this post, or you notice anything else strange happening with your furnace or air conditioner, you should call an HVAC technician immediately. It might seem like a waste of money to hire a technician for every little problem, but these small issues can easily become big ones if left alone for too long and wind up costing you significantly more in repair bills or replacement costs.


If you have any other questions about furnace troubleshooting, or you think there might be something wrong with your furnace, you can give Valley Comfort Heating & Air a call today at (707) 539-4533 or get in touch with us here through our website. We’ve been serving Marin, Sonoma, and Napa Counties for years now, and we’re confident we can help out with any furnace-related issues you might come across.


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