As a brand new junior HVAC technician, it’s likely you’ll start out by working on preventative maintenance tasks like changing HVAC filters. While this task might be simple, it’s incredibly important to the health of the system.
First we’ll take a look at what filters do and why it’s so important to change or clean them regularly. Then we’ll explain MERV filter ratings and how to change an air conditioner filter.
What is the purpose of HVAC filters?
Furnaces and air conditioning systems have air filters that keep dust and debris out of the equipment. Without HVAC filters (or when they don’t get changed often enough), the system’s components would very quickly become coated with grime.
All that dirt can impede the functioning of moving parts, leading them to wear out more quickly and potentially causing failures. When excess dirt accumulates on the evaporator coil, it’s harder for an air conditioner to absorb heat and cool the space. A coating of grime on the condenser coil makes it harder for the system to release heat outside, potentially causing the compressor to overheat.
When filters get clogged, the reduced airflow can impact cooling capacity and even lead to breakdowns.
That’s why a preventative maintenance visit always includes attention to HVAC filters.
That said, there are higher efficiency filters that can do more to remove some contaminants from the air in addition to protecting system components.
Higher efficiency filters have smaller holes that can trap particles like pollen, mold, pet dander, and even disease-causing bacteria and viruses. Using these filters can improve indoor air quality for your customers and can impact their health as well as their comfort.
MERV ratings tell you about the efficiency of an HVAC filter and the size of the particles it can trap and keep out of the equipment and the air.
Understanding MERV ratings for HVAC filters
You may have already heard about MERV 13 filters when New York City recommended their use in commercial spaces due to the Covid-19 pandemic.
So what do MERV ratings for filters mean? MERV stands for Minimum Efficiency Reporting Values, and the higher the MERV value, the better the filter is at trapping tinier particles. Common HVAC filters are usually MERV 7 or 8. MERV 13 filters can trap smaller particles and it was thought that their use might be able to trap some Covid particles and help to reduce transmission. That’s why MERV 13 filters became very difficult to get for a while.
To trap the tiniest particles that can cause allergies and other respiratory issues, super high efficiency HVAC filters called HEPA filters are needed. HEPA filters have MERV ratings of 17 or higher.
However, it’s important to understand that there are risks to using very high efficiency filters. Not every system can accommodate these filters due to their size (they won’t fit in the system’s filter housing). Also, higher efficiency filters reduce the air flow within the system and cause pressure drops that decrease cooling power.
How often should you change HVAC filters?
In many cases, it’s sufficient to change HVAC filters two to four times each year when you visit the customer to do a tune up. However, some environments may require more frequent filter changes. For example, a factory with a high concentration of airborne fiber or smoke particles, or a restaurant with cooking grease in the air, may need much more frequent filter changes.
The EPA actually recommends checking filters monthly during times of peak usage to make sure they are not clogged.
Chances are, you’re not visiting most customers that often for maintenance. However, you can easily teach them to check and replace their own filters. It’s a great idea to get them a supply of the correct filters so they won’t use the wrong ones and possibly cause damage to the system.
How to change HVAC filters
HVAC filters can be disposable or reusable. For the disposable ones, you’ll just remove and discard the dirty one and insert a new clean one. If a system has reusable filters, you’ll clean it and put it back.
Obviously every system is a little different, but these are the basic steps:
1. Power off
Don’t risk your safety. Switch off the power at the unit and at the circuit breaker.
2. Remove the old filter
Slide the filter out of the housing.
3. Check the filter’s condition
Is it clogged? If you hold it up to the light and you can’t see much light coming through, it needs changing. Even if it’s been in use less than the time recommended by the manufacturer, replace it anyway.
4. Safely dispose of the old filter
Determine if the system has disposable or reusable filters. A disposable filter typically has a cardboard frame and a paper or fiber mesh surface. A reusable one has a metal frame and a special coating to make it washable.
If it’s a disposable filter, put the old filter in a plastic bag and remove it from the space to avoid spreading any contaminants.
5. Clean reusable filters
If you’re cleaning a reusable filter, check the manufacturer’s instructions for washing. You’ll probably just need to rinse with water and let dry completely. Or in some cases, you can just vacuum away the dust.
6. Insert a clean filter
Now you just need to put it back in the right way. An arrow on the filter’s frame shows you the direction that air should flow through the filter, which is always away from the return air duct and toward the air handler mechanism. When you insert the filter back in the housing, make sure that arrow points away from the return and toward the air handler.
Learn more HVAC basics
Looking to start a career as an HVAC technician? Check out these resources to help you boost your knowledge.
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