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Old 04-14-2007, 09:02 PM   #1
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Furnace filter ?


OK, this may sound dumb to some/many of you, but one has ever been able to give me an educated answer to my question. My furnace uses the 4 or 5" thick filters (I can't remember which off the top of my head) which cost about $30 each. The 1" filters cost a couple bucks each. Why can't I just buy 4 or 5 of the 1" filters and put them together instead of paying at least $20 more for the single, 4" thick filter?

Most people just dismiss this with no factual reason because they have never seen it done. The guys at Home Depot / Lowe's where I buy the filters have no clue, and even my old environmental engineering instructor at college couldn't give me a definitive answer.

Any advice is appreciated. Thanks.

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Old 04-14-2007, 09:08 PM   #2
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Furnace filter ?


The volume of airflow thru your system would not filter properly with the thinner filters or stacking them together. You need the thicker filter.

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Old 04-15-2007, 04:48 PM   #3
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Furnace filter ?


You don’t want to use 4 or 5 filters stacked together because the huge drop in airflow it would create, if your furnace and ductwork was sized by the book then the installers figured the air drop across the existing 4” filter and made accommodations for it by increasing the size of the ductwork or fan.
You could replace the big filter with a thinner one with not major complication, the only thing that comes to mind is the dehumidification in summer time but if you don’t have A/C don’t need to worry about.
if you are concerned with indoor air quality look into getting an electronic air cleaner, those big filter do more harm than good.
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Old 04-15-2007, 05:43 PM   #4
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Furnace filter ?


ej72,

The big filter is a 6-12 month filter. Meaning you only need to change it every 6 - 12 months. Also, the big filter has more surface area so as it gets dirty it does't restrict air flow. I'm guessing your big filter is a MERV 8 or 10 filter. If you purchase 5 - 1" filters the same merv rating it would cost you $50 dollars or more; you would have to change the front filter every month and you still have less air flow. By the way, MERV is a rating for filters. The higher the number the more dirt it catches and the more it restricts air flow especially with the 1" filters.
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Old 07-05-2009, 06:03 PM   #5
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Furnace filter ?


yh its a big one though ...
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Old 07-05-2009, 07:46 PM   #6
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Furnace filter ?


The 4 and 5" media filters are pleated. With that many pleats. it has a much greater surface area for the air to go through.
The surface area is a single pass.

If you used 4-1" pleated air filters. The surface area is in series.
In series, this becomes a greater pressure drop, and restricts air flow from day one.

An OEM 4" media air filter may have a pressure drop of .15" brand new at 1200CFM.

4-1" pleated air filters may have a pressure drop of .3" or more brand new at 1200CFM.

While the 4" may load up in 6, 9, or even 12 months. The 4-1" filters will load up in 20 to 30 days.

So you would end up replacing them atleast once a month. So multiply their cost by 12, is it realy any cheaper.

Not to mention the harm it could do to your equipment by reducing air flow even when new. Let alone 15 days later.
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Old 07-09-2009, 08:30 AM   #7
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Furnace filter ?


Quote:
Originally Posted by hvactech View Post
You don’t want to use 4 or 5 filters stacked together because the huge drop in airflow it would create, if your furnace and ductwork was sized by the book then the installers figured the air drop across the existing 4” filter and made accommodations for it by increasing the size of the ductwork or fan.
You could replace the big filter with a thinner one with not major complication, the only thing that comes to mind is the dehumidification in summer time but if you don’t have A/C don’t need to worry about.
if you are concerned with indoor air quality look into getting an electronic air cleaner, those big filter do more harm than good.
i'd have someone check and see if your sustem was designed to have such a rrestrictive filter installed or was it just a sales gimmick tossed in as a freebie by a contractor. what hvactech said about doing more harm than good is valid . you can install an electronic filter in the same space easily.. check it out you need to validate your airflow , too low a flow will shorten the life of your heat and cooling eqp't...........Jack


Last edited by psilliman001; 07-09-2009 at 08:32 AM. Reason: add missing word
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