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  1. #1
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    Nov 2008
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    Confused Return air Multi-Duct run Placement and design questions

    OK so I have read A few threads that touched on this subject but nothing clear enough and its been a while..

    So question,

    1. Return Ducts more then one run on a single system-

    A. If there is more then one run lets start with two runs to a single plenum,

    Ok so i have been told for best static and air flow it might be best two not only run two seperate ducts to indoor unit but also two separate filters, easily done if you choose to use separate filter bases in ceiling at beginning of run in the home etc

    However if you want to use multiple 4-6" media bases to have a better filter and lower static whats the best way(location) to mount these?

    let me pain a picture,

    example 1

    I have a fan coil horizontally mounted in an attic apace with a single metal plenum ,

    I have to assume you would attach plenum to fan coil/air handler and then cut a hole to size of each filter base you want to mount on each side of the single metal plenum?

    If so you would then put filters in and doors on then test static but where would you place static tips once you do this?

    If not proper how would you install this in the same situation?

    I am again assuming this is only way but lets sub a furnace in instead of a fan coil/air handler ,

    would it be easier to install one media filter directly to side cut in furnace and and then the other at natural bottom furnace return opening and attach a plenum to it and then the duct? if you did do this where would you place the static tip and test tesp for return?

    I'm assuming you cant really do it this on a fan coil/air handler because the coil is on the return side and blower is ahead of it ? or am i wrong ?

    example three which if i did use the single plenum with two filter base mount on each side as example 1 states but had three return runs whats the best placement for the third run??

    I have always wondered why this is best using two bases instead of one except media surface area but air is still going through one access provided for return thats why on the furnace i wondered if using one side mount and one horizontal mount is better?


    I can use any and all help with some details and ideas on how some of you guys would do this in all examples? remember that space is limited alot of times and putting weird T or L multiple section plenums on a single unit may not work..

  2. #2
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    895
    Why not ceiling return air grill w/ filter at each location on ceiling.

  3. #3
    Join Date
    Nov 2008
    Location
    DFW,TX
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    Quote Originally Posted by Timber View Post
    Why not ceiling return air grill w/ filter at each location on ceiling.
    Because for one 1 inch pleated filters especially the better ones have almost 50% or in some cases dbl the static pressure as well as changing 2-4 filters in ceilings especially high ceilings that require a tall ladder to replace is not going to encourage regular filter replacement.

    U being from TX have had to realize by now that just about every home has bad high static duct systems and a lot is under sized returns so i want better options to offer customers on new installs.. if you dont correct static issues on the upgrades especially the VS systems you will have issues that you will now own.. better to charge and correct up front that have a mad customer..

  4. #4
    Join Date
    Sep 2006
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    1,253
    Quote Originally Posted by acguytx View Post
    Because for one 1 inch pleated filters especially the better ones have almost 50% or in some cases dbl the static pressure as well as changing 2-4 filters in ceilings especially high ceilings that require a tall ladder to replace is not going to encourage regular filter replacement.

    U being from TX have had to realize by now that just about every home has bad high static duct systems and a lot is under sized returns so i want better options to offer customers on new installs.. if you dont correct static issues on the upgrades especially the VS systems you will have issues that you will now own.. better to charge and correct up front that have a mad customer..
    Use something like this in your filter grille:
    Attached Images Attached Images

  5. #5
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    DFW,TX
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    Quote Originally Posted by mchild View Post
    Use something like this in your filter grille:
    I agree that will work in a lot of cases but when its not an option then i still want to explore my original questions.. thx

  6. #6
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    895
    You could just use the 4 inch honeywell filter base, attach to horizontal unit then attach your return plenum, cut your 16 and 18 inch round holes for the sticky back type taps.

    The honeywell base will also accept the electronic filter assembly or you can just use a 4 inch filter...

  7. #7
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    Nov 2008
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    I assume some of you arent picturing my questions from your answers,

    Ive been told a good way to alleviate high static on the return side is to use more then one filter base with multiple duct runs especially when installing media filters 4-6" etc as its increases the media surface area where you dont have all the air from two ducts runs running into one filter. it seems like a logical choice to use two bases/filters before the unit to not have a proverbial traffic jam of air trying to be forced through one filter..

    One is this true? if so how do you mount them , configuration and really does it help a lot because you still only have the one entrance into return side of furnace/ air handler after ??

    again id like to explore my original questions with people who have had success using two media bases on both an air handler/fan coil and furnace?

    should this be moved to the airflow/duct section maybe?

  8. #8
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    Nov 2008
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    DFW,TX
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    no more input?

  9. #9
    Join Date
    Feb 2003
    Location
    garland, texas
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    666
    Gas or fan coil. Install one long common plenum on return side. Buy 5' rex racks and rex plenums from Insco. Install as far back on common plenum as possible. Attach duct to rex plenum. I cant see a need for more than 2-5" filters on a 5 ton unit. We've have done a plenum on bottom and one on side in horizontal. Some manufacturers say bottom end only in horizontal position. Use transitions where necessary. We see a lot of big filters installed with 50% of the case blocked off on one side or both. If the return static goes down the supply will go up. Place static probes in usual place, one at entrance, one at exit of equipment unless you want to check drop across filter. If you use one bottom and one side just average the 2.
    Last edited by nvr2old; 10-29-2012 at 05:35 PM.

  10. #10
    Join Date
    Feb 2003
    Location
    garland, texas
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    Are you looking to just lower static to be in factory specs or to achive a cfm at a certain static, or as much cfm as possible?

  11. #11
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    Nov 2008
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    Quote Originally Posted by nvr2old View Post
    Are you looking to just lower static to be in factory specs or to achive a cfm at a certain static, or as much cfm as possible?
    just a better way to lower static on return side and get as much balance's to the cfm from return to supply..

    really just curious as to the application because ive been told that two media filters, one on each return line will lower static as opposed to one after the plenum right before the equipment. So it will lower static by increasing surface area?

    so with different types of installs i want to know how these media bases are inatalled and where ie a furnace where you could conceivably put one at end of unit and one in a side cut OR YOU COULD PUT ONE ON EACH SIDE OF A BASIC PLENUM ..

    however on a Fan coil/air handler you can side cut a unit so you would have to put one on each side of a single plenum BUT BEING THAT EITHER APPLICATION STILL ONLY HAS A CAPACITY TO STILL BRING ALL THIS CFM THROUGH THE SAME FACTORY OPENING.

    SO THAT SAID DOES THIS METHOD ACTUALLY WORK IN LOWERING STATIC AND IF SO HOW MUCH AND IS IT REALLY WORTH IT..??

    I AM GOING TO EXPERIMENT ON MY OWN unit in the attic but wanted some feed back before i start..

  12. #12
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    Feb 2003
    Location
    garland, texas
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    Yes it lowers static on the return side significantly. Its worth it. Just remember the static will go up on supply side if duct is to small. One of the ACCA alphabet manuals recommends you choose a furnace with a blower capacity that meets your desired cfm in medium speed at desired static.

  13. #13
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    Quote Originally Posted by nvr2old View Post
    Yes it lowers static on the return side significantly. Its worth it. Just remember the static will go up on supply side if duct is to small. One of the ACCA alphabet manuals recommends you choose a furnace with a blower capacity that meets your desired cfm in medium speed at desired static.
    ok so do you recommend using the single plenum method on all installs and just simply attach a media filter base on each side of a single plenum and bring in a separate return duct to each base?? or will it make a difference on furnaces bringing in a side return for one run and one on the end/bottom of furnace?

    thanks in advance

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