Do Clean Air Filters Really Work in My Home?

Home Improvement

The clean filter on the right will only work properly if it becomes dirty like the used one on the left.
iStockphoto.com/maco0708

Your heating and air-conditioning system pulls air from a room, cools or heats it, and then circulates the air through ducts to other rooms in your home. The air filter is located where the system draws in air to capture air-borne particles and prevent them from blocking the blower or clogging the coils. Clogged coils impair the air’s temperature regulation and can cause damage to the system. Therefore, a clean air filter helps your heating and cooling system work efficiently, protect the system, and prolong its lifespan.

Filters also help to prevent dust from accumulating in your ducts or being dispersed into other rooms of your home. In recent years, air filters have become more important to homeowners as manufacturers have developed filters that use the heating and air system to remove microscopic particles such as pollen, dust, pet dander, bacteria, plant and mold spores, and even smoke from the air in your home.

It is often said that clean air filters save energy and money, which is why it is important to regularly change or clean the filters in your home’s heating and air conditioning system. However, what exactly do these filters do? How can you tell if they are working? How often should you change them, and what should you do if they appear clean when it is time to replace them?

In the following pages, we will examine the function, types, rating system, and maintenance of air filters for your home’s heating and air-conditioning system. We will also explore common problems that prevent filters from working properly.

What is the Purpose of Air Filters?

The MERV rating of a filter indicates the percentage of particles that it captures as air passes through it. In general, a filter with a MERV rating of 6 can capture up to half of the particles in the air, while a filter with a rating of 8 can trap 70 to 85 percent of air-borne particles. Filters with a rating of 11 or higher are capable of making the air up to 95 percent cleaner than when it entered the filter [source: Lowe’s].

A properly installed and functioning heating and air system circulates the air in your home every hour, drawing it through the filter in the process. The effectiveness of the filter in cleaning the air depends on its MERV rating.

The term MERV stands for Minimum Efficiency Reporting Value and is used to indicate the size of particles that a filter can remove from the air passing through it. The ratings range from 1 to 16, with a higher number indicating a higher cleaning efficiency as it can filter smaller particles from the air. The disposable filters made of jumbled fiberglass or natural fiber strands are typically 1 inch thick and have a MERV rating of 1 to 4. Pleated filters made of nonwoven, disposable fabric have smaller pores and higher MERV ratings of 3 and above depending on the density of the fabric and the number of pleats. Some pleated filters are charged with static electricity to attract and hold air-born allergens. As the filter gets dirty, the particle catching efficiency increases, but this can lead to a restriction of the air-flow through the system, causing it to work harder and drive up heating or cooling bills. Therefore, it is important to check filters at least monthly and change them when dirty. The MERV rating on the packaging indicates the size of particles, measured in microns, which a filter can capture. The higher the MERV rating, the smaller the particle it can grab. When it’s time to change the filter, it should look dirty with a build-up of dust on the duct side.

If your air filter appears clean even after the recommended period, there are a few things you should investigate. Firstly, check if the filter fits properly into the holder. If it’s too loose or small, air may circulate around it instead of through it. Secondly, make sure the filter is installed the correct way up, with arrows on the frame pointing toward the fan. Thirdly, check if the filter is suitable for the task at hand – a filter with a higher MERV rating will be more efficient at cleaning the air. Finally, check your system’s rate of air exchange – if it’s running for less than 15 minutes per cycle or more than three cycles per hour, it may not be creating the desired rate of air exchange. Your home environment and usage patterns can also impact the frequency at which your air filter gets dirty. If your home is well sealed, doesn’t have pets or dust-prone furnishings, and you vacuum frequently, your filter will collect fewer particles. Remember that the system filters air only when it’s running, so if you don’t use your heating or air conditioning for a month or two after installing a new filter, it should still be fairly clean. For more tips on saving energy, see the links below.

FAQs about Air Conditioner Filters

How frequently should you replace your HVAC filter?
It is recommended to replace your air filter between one to three months after installation. Signs that indicate you should replace your air filter include a buildup of dust and gray, ashy-looking material on the duct side of the filter.
What is an HVAC filter?
The HVAC filter plays a critical role in your home’s heating and cooling system. These filters trap airborne particles that are sucked in with the air and prevent them from blocking the blower and clogging up the coils. The primary purpose of the air filter is to help your HVAC work efficiently, keeping it running smoothly and protecting it so that it lasts longer.
What MERV rating air filter should I use?
The minimum efficiency reporting value (MERV) is an industry-standard rating system to help consumers understand how well an air filter cleans the air passing through it. A MERV rating of 6 indicates that the basic filter will capture up to half of the particles in the air, while a rating of 11 or higher indicates that the air filter will capture up to 95 percent of the particles in the air.
Where can I find the HVAC filter?
The HVAC air filter is located where the air is pulled into the air conditioning or heating system. Your HVAC then pulls it over coils to heat or chill it, and then blows the tempered air through ducts to the other rooms in your home.
What happens if I don’t replace the HVAC filter?
If air filters are not replaced regularly, they eventually become clogged and prevent air from passing through them. Clogged filters and coils prevent the air from heating or cooling, damage your HVAC system, and increase your energy bill.

Additional Information

Related HowStuffWorks Articles

• How Home Floor Plans Work
• How Roofing Materials Work
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• Installing a Fiberglass Shower and Tub Surrounds

Sources

• Autry, James A. and Gerald M. Knox, eds. Better Homes and Gardens Complete Guide to Home Repair, Maintenance & Improvement. Des Moines, IA: Meredith Corporation, 1980.
• Barnett, Dwight. “Low Air Pressure and Dust.” Home & Garden Television. 2009 (Accessed 4/27/2009). http://www.hgtv.com/home-improvement/low-air-pressure-and-dust/index.html
• Brumbaugh, James E. Audel® Heating, Ventilating and Air Conditioning Library, Volume 1. New York: Macmillan Publishing Company, 1986.
• Furnace Compare. “Frequently Asked Questions about Furnace Filters.” Furnace and Air Conditioner Filters. 2009 (Accessed 4/27/2009). http://www.furnacecompare.com/faq/furnace_filter_faq.html
• Home & Garden Television. “Keep Dust Down.” Home Improvement. 2009 (Accessed 4/27/2009). http://www.hgtv.com/home-improvement/keep-dust-down/index.html
• Home & Garden Television. “Spring Cleanup List Begins with HVAC.” Home Improvement. 2009 (Accessed 4/27/2009). http://www.hgtv.com/home-improvement/hvac-a-spring-fix-up-checklist/index.html
• Howarth, Peter and Anita Reid. Allergy-Free Living. Great Britain: Mitchell Beazley, 2000.
• Huber, Jeanne. “The Dirt on Furnace Filters.” The Washington Post, January 19, 2006. (Accessed 04/27/2009). http://www.washingtonpost.com/wp-dyn/content/article/2006/01/18/AR2006011800470.html
• INDA. “Air Filters for Your Home.” International Nonwovens & Disposables Association. 2009 (Accessed 4/27/2009). http://www.inda.org/enduses/homefilters/index.html
• Lowe’s. “Choosing a Home Air Filter.” Buying Guides. 2009 (Accessed 4/27/2009). http://www.lowes.com/lowes/lkn?action=howTo&p=BuyGuide/ChooseFurnaceFilter.html
• Williams, Freddie. Instructor of Air Conditioning Technology, Lanier Technical College, Oakwood, Georgia. Interview, May 5, 2009.

FAQ

1. Do air filters need to be dirty to work effectively?

No, air filters do not need to be dirty to work effectively. In fact, clean air filters can actually improve the air quality in your home. Clean filters are able to trap more pollutants and allergens, which means they can help to reduce the amount of dust and allergens in the air. Additionally, clean filters can help your HVAC system to run more efficiently, which can save you money on your energy bills.

2. How often should air filters be changed?

The frequency with which air filters should be changed depends on a number of factors, including the type of filter, the level of air pollution in your home, and the size of your home. As a general rule, it is recommended that air filters be changed every 30-90 days. However, if you have pets or suffer from allergies, you may need to change your filters more frequently.

3. What are the benefits of using clean air filters?

There are several benefits to using clean air filters in your home. Clean filters can help to improve the air quality in your home by trapping pollutants and allergens. They can also help to reduce the amount of dust and debris in the air, which can benefit those with allergies or respiratory issues. Additionally, clean filters can help your HVAC system to run more efficiently, which can save you money on your energy bills and extend the life of your system.

4. Can air filters be cleaned and reused?

Some types of air filters can be cleaned and reused, while others are designed to be disposable. If you have a reusable filter, it is important to follow the manufacturer’s instructions for cleaning and maintenance. In general, reusable filters should be cleaned every 3-6 months, or as often as necessary to keep them free of debris and dust.

5. How can I tell if my air filters are working?

You can tell if your air filters are working by checking the amount of dust and debris that accumulates on them over time. If your filters are clean when you change them, it is a good sign that they are doing their job. Additionally, you can monitor the air quality in your home by using an air quality monitor. If the air quality improves after you change your filters, this is a sign that they are working effectively.