are merv filters bad for an ac?

dland2000June 14, 2011

I recently had a energy efficiency consultation done at my home. They inspector told me that using MERV rated AC filters is a bad idea because the mesh is so fine than its hard for the system to pull air through it, which can shorten the life span of the air handler. He suggested using the "cheaper" filters and a HEPA unit inside the house if I was concerned with allergens in the air.

I'm not really concerned with allergens that much but I do have a number of animals that shed a lot of hair and dander. Perhaps he's right that it being harder on the unit to use a denser filter, but wouldn't a less dense filter allow more hair and dander through into the air handler? That seems bad too.

I live in Texas where the AC runs quite a bit from June through October. I use MERV-8 filters.

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pure nonsense

assuming ductwork is sized correctly both supply and return along with decent sealing, I see no problems with a MERV 8 rated "pleated" filter whether 1" or 5".

you must have good protection of your evap coil, and blower motor plus a measure of reasonable indoor air quality.


    Bookmark   June 14, 2011 at 5:29PM
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Tiger is correct that those filters can certainly be used if everything is sized properly... that being said are you having air cooling issues? You'd stated you got an efficiency check done... so strictly financial concerns or is something amiss with the temperatures in your home? All I'll say is that using cheaper filters can be better idea if you're having air flow issues and for the most part they'll still catch pet hair, dust, and dander. The tradeoff is the dust that does slowly make it into your system and is eventually recirculated.

    Bookmark   June 14, 2011 at 7:00PM
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and the dust that damages blower motor, evap coil, not to mention that re-enters your home's living area.


    Bookmark   June 14, 2011 at 7:28PM
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another idea could be to use a larger sized, but decent merv type of filter.

If your current filter is too restrictive, then a better solution than less filtration may be more filter surface area.

Don't guestimate on these things, have someone help you who understands all of this.

    Bookmark   June 15, 2011 at 8:09AM
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Thanks for the help guys. So when you say a larger filter, I assume you mean that the filter is thicker but less dense so it ends up catching the same amount of particles but the air can flow through it easier? If so, I don't think my system will currently accommodate a thicker filter.

Also, I don't have any cooling issues at the moment. The energy consultation was just for piece of mind. The system works well and I recent checkup resulted in a clean bill of health.

    Bookmark   June 16, 2011 at 3:16PM
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I am lucky in that my filter tray has tabs that bend out to fit a 20x25x1 but the tray is a touch over 4" deep. I bent the tabs out of the way and dropped a 4" filter in place. I later cut the filter apart and pulled the media out straight. It was like 15-20 feet long total length. I did not measure a 1" but that 4" filter has a ton of media. I still try to run something close to a merv 8 but mainly to protect the coil and blower.

    Bookmark   June 17, 2011 at 11:18PM
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when I say larger filter, I mean more square inches of surface area.
This can be done with a duct transition, or by using 2 filters angled 45 degrees instead of 1 filter straight in the ductwork.

    Bookmark   June 18, 2011 at 6:04PM
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