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  1. #14
    Join Date
    Feb 2004
    Location
    chicago suburbs
    Posts
    4,422
    16x25 is more than enough for 1200 cfm. don't worry.
    FILL OUT YOUR PROFILE!!

  2. #15
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Originally posted by coolcray3
    so you are going to tell me that if you put a 16x25 filter rack on both sides of any furnace with the proper size duct its not going to beenough.
    No that's not what I'm saying. In your post it liked you suggested almost 2000 CFM could be pulled through a 16x25 filter. If that's not what you were saying I apologize.

  3. #16
    Join Date
    Jun 2005
    Posts
    178
    no i was just saying that if the installer put a 16x25 filter rack on a 3 ton system and the ducts are propperly sized to handle it that the system would be fine and it common practice to install a 16x25 filter rack on the side of the furnace that has from 1 1/2 to 3 1/2 tons of cooling installed on it.

  4. #17
    Join Date
    Feb 2004
    Posts
    2,597
    Originally posted by coolcray3
    no i was just saying that if the installer put a 16x25 filter rack on a 3 ton system and the ducts are propperly sized to handle it that the system would be fine and it common practice to install a 16x25 filter rack on the side of the furnace that has from 1 1/2 to 3 1/2 tons of cooling installed on it.
    just because it's common practice doesn't mean it's right.

  5. #18
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by billva
    Originally posted by coolcray3
    no i was just saying that if the installer put a 16x25 filter rack on a 3 ton system and the ducts are propperly sized to handle it that the system would be fine and it common practice to install a 16x25 filter rack on the side of the furnace that has from 1 1/2 to 3 1/2 tons of cooling installed on it.
    just because it's common practice doesn't mean it's right.
    Exactly,

    The only way to verify that filter is adequate for 1200 CFM is to test either the pressure drop across it or to check the face velocity of the filter.

    If it is not sized big enough which IMO it is not the filtration of that media will suffer & filter bypass will occur if the filter rack is not sealed properly
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  6. #19
    Join Date
    Jun 2005
    Posts
    178
    well i guess your right there and almost every installer out there is wrong.

  7. #20
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by coolcray3
    well i guess your right there and almost every installer out there is wrong.
    I used to do the same thing & not think twice about it, then I started measuring the airflow on what we installed & it was the biggest kick in the teeth I had ever gotten.

    The only way to say it is working properly is to test it & if those installers are not doing that I can safely say they don't have a clue if it's working right.
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  8. #21
    Join Date
    Jun 2005
    Posts
    178
    well if there wasnot enough air flow you would know as soon as you put a set of gauges on it and checked the pressures. and it still comes down to the fact that the manufactures give you a 15 x 24 knock out area on the unit to install the filter rack and have been doing this for ever.why is that

  9. #22
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Some contractors have ben using a .10 Friction Rate forever,doesn't mean it works properly.

    You need to check the filter PD ,but that won't tell you if it's right either,it's the ESP of the duct "system",compared to the fan chart for that model and the airflow required.

    The velocity along in this case will be to great for good filtration.

  10. #23
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    a pleated filter also has more surface area.
    never say never

  11. #24
    Join Date
    Jun 2005
    Posts
    178
    pleated filters also cause more restriction.

  12. #25
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Originally posted by coolcray3
    well i guess your right there and almost every installer out there is wrong.
    Most don't care. I never use the supplied filter racks on installs. You keep mentioning the cut out size on the furnace as only being 14 or 16 x25 and your correct. How we do it is make a transition from the furnace to a larger filter rack, but in 95% of our installs we use a media filter which is done the same way with a transition. Filters being to small are one of the biggest reasons for equipment failure simply because of airflow and the fact that few change filters as often as they should which makes using a smaller filter even worse.

  13. #26
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by coolcray3
    well if there wasnot enough air flow you would know as soon as you put a set of gauges on it and checked the pressures. and it still comes down to the fact that the manufactures give you a 15 x 24 knock out area on the unit to install the filter rack and have been doing this for ever.why is that
    The manufacturers also set the fan speed for cooling in the high speed setting, does this also mean that is where it is supposed to stay? On variable speed motors the dip switches are set by the manufacturer does that mean we should leave them alone?

    You need to take a look at the recommended face velocities for each type of filter media before you can even begin to size them properly.

    Just because there is a 15 X 24 opening does not mean the filter is to automatically be sized to that opening.

    I would not depend on my gauge readings only to identify an airflow issue either, there are other methods that are much more reliable.
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