Effects of a Clogged HVAC Air Filter

Dirty Filters will cause bad effects to your air conditioner or heat pump

What happens when your filter clogs up with dust and debris? The effects of a clogged HVAC air filter in your air conditioner or heat pump can cause failure of the system operation that will result in a call for an air conditioner repair service. Furthermore, dirty AC air filters can have a detrimental impact on your AC and heating systems.

An AC, heat pump, gas furnace, electric furnace, or even an oil furnace needs the proper amount air flow across the coil or heat exchanger to operate properly. Therefore, when the filter clogs the air flow is minimized the blower works harder and harder to pull the proper amount of air across the coil or heat exchanger. What are the effects of a clogged filter in your HVAC system?

Serious Harmful HVAC Issues | Effects of a Clogged HVAC Air Filter

  1. Dirty AC Air Filters cause your air conditioner to stop cooling
  2. Clogged AC filters will cause your air conditioner to freeze up and when it thaws the water from the melting ice can overwhelm your condensate drain and cause water damage
  3. Cause a serious mechanical issue with your compressor in your air conditioner or heat pump technically referred to as liquid slugging
  4. Lastly, dirty filters will cause your furnace and/or heat to stop heating

Dirty HVAC Air Filters

  • As the system airflow is reduced from a restricted and clogged filter your air conditioner or heat pump (in cooling mode) evaporator coil will begin freezing up resulting in less and less air flow from the supply vents. The refrigerant is still flowing through the coils but with no air-flow, there is no heat absorbed into the coils and refrigerant. The refrigerant falls below the freezing point. Any moisture in the air around the coil begins freezing. It effectively turns the air conditioner or heat pump evaporator coil into a freezer. If the air filter is changed then you will still have problems until the evaporator coil is defrosted. With an air-conditioner, you turn it off for several hours to allow it to thaw. With a heat pump, you can simply turn it to heat mode. It will automatically defrost the evaporator coil. However, this problem can cause serious water damage to your home or business.
  • Furnaces with clogged air filters will stop heating. As the air flow is restricted the heat in the heat exchanger gets higher and higher. Designed into every furnace are limit switches that will open when the temperature exceeds a designed temperature. When the high limits open the burners turn off and the heat stops. Many times these are automatic reset switches and will automatically reset when the temperature of the heat exchanger cools but if the clogged air filter is not corrected then the problem will recur and the furnace will not provide the proper amount of heat. Sometimes the limit switch will get stuck in the open position. Furthermore, this results in a service call from a contractor to replace the part.

Pressure in the HVAC System and Dirty AC Filters | Effects of a Clogged HVAC Air Filter

Furthermore, the pressure in the HVAC duct system and air handler are very important. If your system was designed correctly the designer designed the system for a specific amount of pressure. The pressure as recommended by the manufacturer of the equipment. When your filter gets dirty you change the pressure inside the system and by doing so you change the amount of airflow flowing through the air handler and ductwork.

There are other ways to change this pressure inside the ductwork such as closing off too many supply vents, a bad blower motor, or collapsed/restricted ductwork. However, here we are focusing on dirty air filters. We have covered those other things in other articles. Lastly, please browse our other articles for that information to help you learn. Finally, here is an example to illustrate the pressure in the system:

Maintenance HVAC Furnace Filter Basics

From the chart above the manufacturer recommends a design pressure of .05″ water column. Furthermore, if this was your system then it should be designed/balanced to achieve that pressure. At that pressure, we get the other variables. Furthermore, these variables are listed and highlighted on the chart. CFM’s, and temperature rise. This is also the design pressure needed for the evaporator coil to function properly. Therefore, when you have a dirty clogged air filter, you change all that including the pressure, the CFM’s, the temperature rise. Furthermore, you change the proper functioning of the evaporator coil. Lastly, this leads to problems that will affect your comfort.
Air Filter Categories
  • Mechanical Air Filters – This is your typical off-the-shelf throw-away HVAC filter. This filter collects particles in its filtering medium. After it collects so many particles you simply remove it, throw it away, and replace it with another. Note that some mechanical filter media are washable. HEPA (High-efficiency particulate air filters) are also in this category. There are three sub-categories of mechanical air filters. These are:
Mechanical Air Filter Categories
  1. A1 and A2 – these are the standard 1 inch thick filters. These are typically rated MERV 1 to MERV 4. These are the least effective filters and designed for basic protection of your HVAC system and not health.
  2. B filter media’s are 2 to 4 inches thick. These filters typically range from MERV 1 to MERV 12.
  3. C filter media represent the HEPA filters. MERV ratings for these filters exceed MERV 13 and are the most expensive. High-efficiency particulate air filters are excellent for filtering the air but, again, they are the most expensive. An HVAC system with this type of filtering system needs to be specifically designed for this type of filter. Additionally, it is important to make sure these filters do not load up and stop airflow. As noted above, that can have a detrimental effect on your HVAC system.

Other Types of Air Filters

  • Electronic Air Cleaners – The electronic air cleaner does not qualify for a MERV rating. Because its efficiency can change depending on how clean it is. It is important that electronic air cleaners are cleaned on a biannual basis (more frequently in dusty environments) for the best performance. Additionally, these work best when used in conjunction with a mechanical filtering media.
  • Gas Phase Absorption – uses carbon to absorb odors and gases from the air stream. This media is not very effective at removing particulates and is used mainly in laboratory and industrial settings.

Furnace Filter Problems | Effects of a Clogged HVAC Air Filter

The effects of a clogged air filter in your HVAC system can end up causing damage to the air conditioner, heat pump, or furnace so make sure you keep the air filter clean and free of debris. One other big mistake that will have the same effect of closed-off supply vents. Anything that reduces the airflow in your HVAC system is not good for it. Keep the supply vents open and filters clean and avoid costly repairs.

High Performance HVAC

Effects of a Clogged HVAC Air Filter - HVAC

Resource: The Home Comfort Book: The ultimate guide to creating a comfortable, healthy, long lasting, and efficient home

COVID 19 Home Protection

UVC Light to Kill Viruses and Other Airborne Harmful Things that Affect Health

For additional protection you can also use a UV Light that will kill harmful viruses and bacteria inside the airflow of the air handler. In labs researchers used a spectrum of ultraviolet light called UVC to kill viruses. This product requires professional installation so it will turn on and off with the blower fan in your air handler but it will offer the protection you need for you and your family from any viruses.

Click the image to the right for purchase options of the UV light to protect your family.