Here’s Why Your HVAC Filter May Not be Improving Your Indoor Air Quality

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Updated on Oct 23, 2023
5 min read
Here’s Why Your HVAC Filter May Not be Improving Your Indoor Air Quality

Researchers working on indoor air quality (IAQ) have established that human health can be negatively impacted by particulate matter in the air. A primary way to deal with this is by filtering out the indoor air. Heating and air conditioning systems in most homes are responsible for filtering out the air. However, you shouldn’t think you are covered just because you have an HVAC system. This post will tell you why.

1. HVAC System Does Not Have a Filter

You won’t get much filtration if your HVAC system doesn’t have a filter. Some people remove the filter because it is in a difficult to reach spot, such as a crawl space. Or, they may take it out and forget to insert it back. Without a filter you are placing your blower, duct work, furnace heat exchanger, air conditioner coil, and everything else at risk.

2. Air Bypassing Filter

It is possible that your HVAC system may have a filter, but air may bypass it. Your system may have a deep media filter capable of filtering the air. But, if it is installed incorrectly, air will pass right by the filter and into the system instead of passing through it. Bypass means that your air filter is unable to get its job done.

3. HVAC Not Working

Air filters cannot clean the air if there is not enough runtime. There is no filtering when your system is off. However, the trick is not to get a smaller HVAC system that runs continuously. Without the right sized system, you would essentially be cutting down the filtration volume and air flow throughout the system.

4. Airflow is Not Enough

Runtime and flow tend to go together. Low filtration volume is a problem for a variety of reasons. Filters and return ducts are of a small size. This causes undue pressure on the system which tends to reduce air flow. Low air flow and high pressure is a major problem.

5. Filter is of Low Efficiency

You may not get improved IAQ with a standard one inch fiber glass filter. This is because the filter is designed to keep dead spiders, dog hair, and other similar things from getting inside the air handler. Minimum Efficiency Reporting Value (MERV) is the standard rating system for air filters. You can filter out more stuff with higher efficiency rating.

You should get air filters with rating of at least MERV-10 to reduce PM2.5 by 50%. MERv-12 filters can remove up to 85% of particulate matter. However, most HVAC systems with high-MERV filters have a poor design that decreases the air flow.

6. Outdoor Air is Not Filtered

Certain ventilation systems distribute outdoor air using heating and cooling ducts. Outdoor duct in a standard mechanical ventilation system is connected on the return side. Sometimes it just so happens that a careless installer or designer will connect the outdoor air duct downstream to the return side.

This will cause unfiltered air to blow through your house. Not only will this not improve the air quality in your Bay Area house, it will cause the blower, ducts, AC, and heating components of your system to get dirty as well.

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