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Question DetailsAsked on 10/1/2013

Are air filters in HVAC systems really effective?

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2 Answers


Definately effective, if you get a high MERV Rated filter. However the higher rated filters are more restrictive to airflow, so always have the static pressure( resistance to airflow) of the system tested by a Pro, before adding "better" filters. Not all companies have the equipment or knowledge to do this, so call and make sure before inviting them to your home.

Your duct system can be modified to handle more restrictive filters, maintaining the required airflow is critial to proper operation.

Carrier has the Infinity Air Purifier that is MERV 15 rated, you'll see on the chart below this is a high rating for a home. Your indoor coil ,when wet in the cooling mode, is about a MERV 6, don't let you indoor coil be the "best" filter in the system, it will become clogged and is costly to clean. MERV 10 or 12 is my recommended minimum.

Here's a MERV chart, that should help you decide;

As always, find the HVAC guys on Angie's List!


Answered 6 years ago by BayAreaAC


Here are several responses to an earlier similar question that might be of use to you -

The air filter in your forced air system serves a couple of purposes - to remove air pollutants, allergens, and dust from the incoming fresh "makeup" air, to remove dust, lint and allergens from the inside air being recycled within the house (and carpets and clothing release a LOT of dust and lint), to keep these from impinging on and sticking to and reducing the effectiveness of your fan and heat exchangers (furnace and/or A/C), and reduce the amount of such items that is in the airflow so they do not deposit in the vents, ultimately reducing airflow.

Use of good filters is mandatory, but as you can imagine, the more effective they are at catching air contaminants, two things happen - more effective ones are inherently also more resistant to air flow, so using a much more efficient filter than the sytem is designed for also cuts down airflow below the design level, reducing the hating and cooling effectiveness, and potentially overloading the fan or heat exchanger or causing freezing in the A/C evaporator if a combined unit. Also, because they catch more of the contaminants, they also plug up quicker, so have to be cleaned or changed out more often.

Generally, if your filter does not seem to be doing a good job of cleaning the air (assuming the ducting is installed right so the filter cleans both incoming and recycled air), then to install a higher efficiency filter you may need to upgrade to a larger fan unit, or install a speciall filter chamber in the duct, which is much larger than the rest, so the higher efficiency filter presents a much larger surface area for the air to flow through. For instance, a high efficiency filter may have twice the pressure loss across it that an economy mat filter has, so it may need about twice the surface area in the airflow to avoid having to replace the fan unit.

Answered 6 years ago by LCD

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