A/C air handler filter question

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Old 08-09-15, 08:57 AM
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A/C air handler filter question

We moved into our home in December and have an HVAC system. I know my filter size is 20X25X1 because that's what I found when we bought the home but will confirm it in September when I get an annual service. I've been using MERV 8 filters as a sort of good blend but am wondering about over-stressing my HVAC unit. What, if anything, should I focus on? FPM, for example? Or perhaps I can get the cheapest filter and increase my health insurance.
 
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Old 08-09-15, 07:15 PM
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MERV 8 filters are rated for commercial applications with higher pressure blowers. They are too restrictive on most residential units.
 
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Old 08-10-15, 02:53 AM
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Thanks for the reply. But then, what should I use? Note that none of us have allergies and we have no pets.
 
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Old 08-10-15, 05:19 AM
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Furnace filters have become the next big (useless) health sell. People are putting MERV 7's, 8's an 9's in because it's "healthier" and not understanding the science behind it.

Firstly, a MERV 8 was built to remove 75% of particles between 3 and 10 microns. Meanwhile have you looked at the gap(s) between the filter box and the filter? I've seen gaps as big as a 1/2 inch. Maybe the filter was built to handle 3 to 10 microns but I can pretty much promise you your duct system and filter box was not built to that kind of finite scale.

Filters are built to protect the equipment and somehow that has twisted itself into some kind of micron removal system for health reasons. Personally speaking I wouldn't go anything over a 4 because you're just wasting money and restricting your system unnecessarily.
 
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Old 08-10-15, 06:17 AM
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Bob is correct in his comments. Filters are over rated for health reasons and will not typically last the 90 days as advertised.

What I tell my customers when they ask what kind of filter they should buy for their furnace/AC:

Do you have a dust problem? If not then the cheap $1.00 units will filter out large particulate like dog and cat hair and some dust. Will allow lots of air flow.

Do you have allergies or breathing problems and to what degree? If yes, then start with the lower end media that gives some micron filtering ability and work your way up until you find the one that alleviates respiratory concerns. AS you move up the micron filtering range air flow will be resticted and the unit will tend to work harder.

A furnace or A/C filter will not cure breathing problems or clean up the breathable air.
 
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Old 08-11-15, 07:10 AM
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Thanks for all the comments, which certainly make sense to me. I spent a lot of time when we bought the home sealing leaks so I know air comes in from many sources.
 
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