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Question DetailsAsked on 7/3/2013

Is it OK to use the least expensive air filters for my HVAC unit if I replace them monthly?

My HVAC tech told me the expensive ones I was using were too restricting on my 20-year-old unit, making it work harder. He recommended I by the cheap ones and replace monthly.

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6 Answers


No it's not okay to use the cheap ones. However the type you may be too restrictive, and likely are, since he said so.

The fan that circulates air in the home, can only deliver the correct amount of air, if the resistance of the ducts,grills,filters is low enough. The ducts can be modified to lower the resistance and allow better filters to be used. Yo need a very qualified company to do this, there is "science" involved.

Cheap filters will allow too much "stuff" to pass through them, this stuff will collect heavily on and in between the fins, of your indoor cooling coil which is "wet" during the cooling mode, and thus becomes the "better" filter in the system. This will eventually reduce capacity, effieceny, and comfort. To clean a coil impacted by por filters, will cost hundreds of dollars, that could have been spent on modifing the duct system to use better filters.


Answered 6 years ago by BayAreaAC


BayAreaAC is right - using the cheapest, least restrictive filters is sort of like saying that instead of putting mosquito netting around your deck, you are going to use hardware cloth designed to stop bees and flies instead - the problem is, the reason the filter is restrictive to airflow is the filter is WORKING - removing smaller particle size contaminants than the less restrictive ones.

When he said duct modifications can be made to allow use of the higher efficiency filters, he did not mean replacing the ducts throughout the house. What he meant is to put a "filter chamber" or "filter flare" in the duct system (at or near the current filter location) which uses high efficiency filters, but with a larger cross-sectional area, so there are more square feet of filter area. This reduces airflow velocity at the filter, which reduces the restriction. The enlargement amount has to be computed from the rated airflow of the unit, and the measured head loss (difference in pressure) across the filters.

Another way to overcome the problem, at least somewhat, is to increase the fan power and/or size or to add what is called a "negative side" fan - one downstream of the filter, that increases the airflow through the filter. The end result depends on your specific system and might involve a combination of these fixes, though usually filter exposed area is usually the easiest to do.

Answered 6 years ago by LCD


you can also use a pleated merv 6 or merv 7 filter

anything higher will restrict air flow we have a large selection of merv 6 filters in stock

email your size and ill send you a quote

remember shipping is always free

Answered 6 years ago by AbeK


LCD is partly correct, sometimes a larger filter surface area can be the solution, most times space limitations are an issue. Ducts can be modified by adding turning vanes to elbows, better transitions, or adding an additional return trunk duct to another area of the home.

The later solutions are we we commonly do.

Find an expert in duct remediation by calling around and asking, "can you reduce the static pressure of my duct system to allow better filters?" You'll know when you find the right company by the answer you get!


Answered 6 years ago by BayAreaAC


Hi We recommend using the cheep pleated filters and changing them at least once in the spring and once in the fall. It is true for some HVAC units we find that the high dollar store bought filters restrict the air flow, this can cause the evaporator coil to freeze up and can sometimes damage the compressor. If you are suffering from allergies you may want to look at electrostatic air cleaning system. Do some research and see if this is something that will work for you. From Shane of Orange Coast Mechanical. Lake Forest, Ca.

Answered 6 years ago by orangecoastmechanica


Many HVAC contractors are just like any other service professional you call on a few times a year. The more you need them the more money they make. Therefore, if you use cheap filters that allow more crap through the system you'll need to pay them to clean the coils and check the system more often. You should have it checked twice a year anyway. Your contractor may be right and any advice here is somewhat speculative and based on experience with similar situations. If you are unsure about the advice given call another company and pay a tech to look at your system and give his recommendation. Do not tell him/her the other advice you have given until they have given their recommendation. If it matches your contractor was telling the truth. If not, you may need to call a third to settle the debate.

Todd Shell

Todd's Home Services

San Antonio, TX

Answered 6 years ago by Todd's Home Services

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