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Spring has officially sprung here in Texas, and even if your hometown’s still under the Groundhog’s curse for a few more weeks, you’re probably considering replacing those nasty, wintrified heating and a/c filters in your home. Realizing that waking up every day with a stuffy nose may be due to my crap-clogged filters, I hit the big box on a mission. Unfortunately when I got there and saw 300 varieties of air filters ranging from “high performance electrostatic” ($$$$) to fiberglass ($), I realized I needed some guidance. Here’s what I learned.

To make sure you’re selecting the appropriate kind of air filter for your home, consider whether any pollutants (indoors, in your garage/shop, or outdoors) are affecting the air quality inside. Household chemicals, pesticides, mold or mildew, high humidity, improperly vented appliances, standing water or leaks, or (obviously) if anyone smokes inside the house are factors that can be identified and fixed first.

Second, assuming your home filters are designed more for providing healthy air in the living space (as opposed to protecting machines or equipment), take into account how you or your family responds to allergens such as dust mites, pollen, mold spores, smoke, pet dander, and smog. The better quality the filter, the smaller the particles it can capture, and without interrupting the air flow of your HVAC system too much, which is paramount for efficiency. Also, check the MERV (Minimum Efficiency Reporting Value) of the filter: they range from 1-16, and the 12-16 range are the highest quality at 90+% efficiency.

Home air filters are divided into six basic types:

1. Electrostatic air filters – As air passes through the filter, a static charge is created that attracts contaminants. Electrostatic filters are very efficient, provide an excellent balance of efficiency and performance, and are designed to replace panel- or frame-style filters you already use in your HVAC system. They often run at or above 90% efficiency or a MERV of 12-15 (compared to 10% for fiberglass), and come in permanent or disposable types. They can be pricey, running around $70, but they do the job well.

2. Pre-cut or bulk roll media air filter pads – Used mainly by HVAC professionals, media air filters have a very high capacity for capturing particles (up to 30 times more capacity than fiberglass) and the pads can be changed out regularly to fit in a single aluminum frame. The pads are made from dry-tack polyester and are disposable. Media air filter pads are not widely available but can be ordered from web sites such as RiteAir.

3. Pleated air filters – Popular because of their durability and affordability, pleated filters are widely available in a variety of (even oddball) sizes and are one of the HVAC industry standards. Some include electrostatic fibers or carbon or charcoal fibers for odor control. MERV ratings for pleated filters range widely from around 5 to 12; for allergy sufferers the 10-12 range would be best.

4. HEPA air filters – To qualify as HEPA (or high efficiency particulate arrestance), a filter must capture at least 99.97% of particulate matter 0.3 microns in diameter. HEPA filters are used in hospital and surgical rooms or other places where clean, particulate-free air is essential. They have the highest filter capacity of all, but require a lot of maintenance since dirty HEPA filters significantly reduce airflow and can cause HVAC system problems if not kept clean.

5. Activated carbon air filters – Activated carbon is charcoal treated to cause millions of pores to form, increasing surface area. Usually carbon filters are added to another type, such as media air filters, because of their ability to remove odors from smoke, chemicals, gases, and other odor-causing substances around the house. They are not recommended in combination with HEPA filters because HEPAs already reduce airflow.

6. Fiberglass panel air filters – Very inexpensive and (unfortunately) commonly used, “blue” fiberglass filters basically capture about as much dust as chicken wire and leave particles of crap blowing around your HVAC system, in your lungs, and in all your equipment too. It’s best to avoid these if at all possible.

The bottom line? If allergies are a major concern, air filters are probably just one step you need to take to improve air quality in your home, but for the highest quality, go with electrostatic filters, and get the permanent ones like the Boair 5-stage if you can afford it. If you just want a simple, decent quality disposable air filter, I’d go with the pleated filters from 3M’s Filtrete with electrostatic treatment. They range from $7-30 each depending on size and quality, and need to be replaced every 3 months or so.

Filtrete Filters Via Amazon [What’s This?]
Filtrete Filters Street Pricing [Google Products]
Guide To HVAC Filters [Furnace Filter Care]
EPA Guide to Air Cleaners In The Home
Article: Understanding Minimum Efficiency Reporting Value (MERV)

 

11 Responses to How-To: Choose Home Air Filters

  1. BigEdJr says:

    I don’t know. Every “professional” I have spoken to about it say just go with the chepaest you can find and replace them every month.

    Those cheap green or blue ones seem to capture a lot of dust whenever I replace them.

  2. shopmonger says:

    NOT TRUE Big EDJR you need to have a filter with enough surface area, and a tight enough weave to not only get good filtration but also not choke down your air system……… balance is the key

    ShopMonger

  3. DaveD says:

    I got tired of buying expensive disposable filters, so I went with a Web washable with a MERV 8 rating for around $20. Seems to be working well enough…

  4. Chris S. says:

    The reason 1″ fiberglass filters changed monthly are recommended is because most houses (especially older ones) have poorly sized ductwork and cant handle the static pressure drop the more expensive filters create. On a furnace the reduced airflow can result in higher discharge temperatures causing safeties to trip and the unit to overcycle. If its an air conditioner then an over restrictive filter can cause the coil to freeze.

    The best filters to get are the 4-5″ thick pleated filters or filter media. These have a much bigger surface area to allow for increased filtration without overfly restricting the furnace/ac.

    Also I would avoid the washable electrostatic filters. They are nice and all, but you need to actually clean them once a month or so and noone ever does that. Its just like those whole house water filters that are great on paper but in reality most people stop changing the cartridges after the first 6 months and then they are constantly drinking water thats passing through a nasty brown slimy cartridge.

  5. Coach James says:

    How do you fit a 5 inch thick air filter into your air return?

  6. Fabian says:

    “The best filters to get are the 4-5″ thick pleated filters or filter media.”

    Got any links..?

    F.

  7. Chris S. says:

    Usually the 4-5″ filters go in a cabinet like an airbear or the spaceguard/aprilaire
    google search turns up http://www.filtersfast.com/Trion-Air-Bear-cat.asp

    The cabinet just gives a better seal/easy access. Theres nothing stopping you from cutting an opening in the duct and putting some rails in to hold a bigger filter if the return boot is big enough.

  8. Mike C says:

    Hey all, in my mech. engineering background i have learned that better filters stop particles through the depth of the filter, that means a cheap filter will stop lots of stuff but only on the surface, plugging up quickly, increasing pressure drop across the filter and thus increasing load on your fan. More expensive filters have the technology to stop particles throughout the depth of the material, big bits stop first, smaller bits get caught deeper in, this way more of the filter material is used thus prolonging life of the filter without drastically increasing your pressure drop across the filter saving the fan the extra load. Some comments above say that thicker filters increase surface area – not quite: L x W = A thickness does not play a part, pleating the filter increases the acutal surface area (bigger L due to the added length in the pleat) of the fabric which reduces the pressure drop across the filter. Getting a flat filter of the same material would decrease your filter area and thus increase the speed of air through the filter and increase your pressure drop. Thickness plays a part in the depth of collection I mention above – I would think that you would want the material to be coarse at the entrance side and fine at the discharge and should be able to see this if its over an inch or two thick. I go for the 3 pack of 3M 3-month filters (red pkg) as we dont have allergy problems. I spend the extra bucks but pick them up only when I notice them on sale and keep enough spares to get me through to the next sale. If you really want to dial it in, you would need to measure the pressure drop across your filter (differential pressure gauge with 2 ports, one piped to the duct on either side of the filter: search Magnahelic) and replace when the pressure drop gets to the mfgr’s recommendation. Price it out and see which way wins.

  9. John says:

    I was always under the impression that a filter is there only to keep the equipment clean enough to work properly, like the blower and A-coil. Unless you are running your furnace blower 24 hours a day, you aren’t really filtering that much air in relation to total volume in a house. Plus your house would have to be considerably air tight to keep the air filtered, or you are just fighting a losing battle.

    • J says:

      Simply not true; most home systems are engineered to cycle through the cubic volume of your home in about 8-12 min (fan capacity (CPM) 1-1.5 x sqft). Which means, even with windows & doors regularly opened, that new air is likely to be filtered fairly quickly.

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