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  1. #27
    Join Date
    Feb 2001
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    447

    Confused

    Quote Originally Posted by motoguy128 View Post
    More surface area = less restriction. The thicker the pleat, the lower the pressure drop with the same media.
    Quote Originally Posted by smittyii View Post
    M style coils require very good return air flow. unless the return is oversized i wouldn't use a 2" filter on a ruud or rheem M coil.
    You guys seem to be contradicting each other.

  2. #28
    Join Date
    Jan 2009
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    Keokuk, IA
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    Quote Originally Posted by charles2 View Post
    You guys seem to be contradicting each other.
    Maybe he's refering to using a 2" filter vs. a 4" or 5"? A thicker filter of the same MERV rating will have a lower pressure drop. The actual airflow won't change if you have a modulating furnace since it's a vairable speed fan that adjusts it's speed to compensate for restriction up to around 1.0" WC of static pressure. where the fan reaches it's maximum pressure rating at the rated flow rate. Thsi is a genralization because hte model AH or furnace and the size of the coil and outdoor unit will change the maximum static pressure the system can reach at the required flow rate.

    The M style coil probably needs less pressure drop on the filter because it likely more restrictive, so the coil + supply ducts restriction may only allow for 0.2 or less pressure drop across the filter.

  3. #29
    Join Date
    Feb 2001
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    447
    Quote Originally Posted by motoguy128 View Post
    The M style coil probably needs less pressure drop on the filter because it likely more restrictive, so the coil + supply ducts restriction may only allow for 0.2 or less pressure drop across the filter.
    Which once again brings up the question of what disposable pleated filter type/brand has the lowest pressure drop. Around here, Filtrete seems to be the most commonly available brand. Surprisingly, their MERV 8 filter has a LOWER pressure drop than their MERV 7, and their MERV 12 has a LOWER pressure drop than one of their MERV 11's. Why hasn't somebody like Consumer Reports tested filters side-by-side to see what's the best value? And what is a typical pressure drop for a dog-catcher filter?

  4. #30
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    Jan 2009
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    Quote Originally Posted by charles2 View Post
    Which once again brings up the question of what disposable pleated filter type/brand has the lowest pressure drop. Around here, Filtrete seems to be the most commonly available brand. Surprisingly, their MERV 8 filter has a LOWER pressure drop than their MERV 7, and their MERV 12 has a LOWER pressure drop than one of their MERV 11's. Why hasn't somebody like Consumer Reports tested filters side-by-side to see what's the best value? And what is a typical pressure drop for a dog-catcher filter?

    I suspect it has a lot to do with the materials used and design as it related to unit cost and marketing. The higher MERV filter, the more money they can sell it for, so more expensive construction and materials are used. Therefore, while performance of caturing particulate is increased, the air flow performance may initially drop on the first "step" then go down as more money is spent at the next MERV level.

    What I getting at is that more pleats = more surface area but more cost. Finer filter matieral increases cost and improves filter performance but reduces airflow.

    What you've discovered is that it's a marketing driven product. The money spent on color printing for the pretty package alone will confirm that.

    Contacting consumers union about testing different air filters is a good idea. They should test the 3 or 4 most common sizes and average their results. Include EAC's as well as 2", 4" and 5" media. The media filters should use the supplied housings. The 1" filters should use a "typical" filter rack. They could be rated or cost, dust removal, air flow, and lifespan. Lifespan would need to be based on a maximum allowed pressure drop. Maybe 0.4" or 0.5".

    I'm a subscriber, maybe I'll write them a letter. Might be worht if not a full test.

  5. #31
    Join Date
    Apr 2008
    Location
    TEXAS
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    1,701
    no contradiction. theM coil has very high fin density and more surface area than most evaps, and will pull down a heat load very fast. the trade off is it requires a large return with minimal pressure drop. most returns are under sized, therefore you need a filter that will not be restrictive. doesn't matter what brand, i don't pay that much attention to brands and most tech's don't either.
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

    "Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington

  6. #32
    Join Date
    Feb 2001
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    447

    Thumbs up

    I think the reason I thought there was a contradiction is that 2" NONpleated filters have a higher pressure drop than 1" NONpleated filters, but pleated filters are the opposite.

  7. #33
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    Jan 2009
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    Quote Originally Posted by charles2 View Post
    I think the reason I thought there was a contradiction is that 2" NONpleated filters have a higher pressure drop than 1" NONpleated filters, but pleated filters are the opposite.
    That has to do with filter construction. Non-pleated filters are typically the white or blue fiberglass and thicker fiberglass represents a larger restriction. With pleated filters, thicker filters means that the pleats are thicker, so the overall surface area that's presented to the incomming air is greater. This can also be accomplished by having more pleats, like the air filter in your car. But tightly spaced pleats can become easily clogged with larger particles and are more expensive to MFG.

  8. #34
    This article with tests of pressure drop on twenty different filters might help to explain some of the points raised here:

    http://texairfilters.com/news/testsonpressuredrop.htm

  9. #35
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    Feb 2001
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    447
    Now that's the kind of testing I like to see! But Filtrete told me that their 600 model has a pressure drop of .14 at 300 fpm, not the .21 listed in the table. Easy Flow also understates. Obviously someone is lying or incompetent. As I contact mfrs, I'm getting numbers all over the map: A MERV 11 with a lower pressure drop than a MERV 7, and a MERV 7 with a lower pressure drop than a MERV 4 (dog catcher). I fear their numbers cannot be trusted.

    Another variable I'm seeing is the recommended pressure drop at changeout: I have seen .5 and 1.0 recommended. Anybody know why the difference?

  10. #36
    Join Date
    Jul 2008
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    551
    Quote Originally Posted by charles2 View Post
    Now that's the kind of testing I like to see! But Filtrete told me that their 600 model has a pressure drop of .14 at 300 fpm, not the .21 listed in the table. Easy Flow also understates. Obviously someone is lying or incompetent. As I contact mfrs, I'm getting numbers all over the map: A MERV 11 with a lower pressure drop than a MERV 7, and a MERV 7 with a lower pressure drop than a MERV 4 (dog catcher). I fear their numbers cannot be trusted.

    Another variable I'm seeing is the recommended pressure drop at changeout: I have seen .5 and 1.0 recommended. Anybody know why the difference?
    are all manufacturers giving you numbers with the same variables? It is easy for a MERV11 filter to have a lower pressure drop than a MERV 7 if the 11 is a bigger filter or its test was run at a lower FPM.

  11. #37
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    Feb 2001
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    447
    Yes, I'm comparing apples to apples, not apples to oranges. Same dimensions and fpm. Only the filter media differs.

  12. #38
    Join Date
    Jul 2008
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    551
    Quote Originally Posted by charles2 View Post
    Yes, I'm comparing apples to apples, not apples to oranges. Same dimensions and fpm. Only the filter media differs.
    what are the exact constants between all manufacturers? Seems unlikely they all ran tests with the same size filter.

  13. #39
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    Feb 2001
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    447
    1" thick and 300 fpm. The other dimensions have no effect on pressure drop, but I'm interested in 16" x 20".

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