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  1. #1
    Join Date
    Jun 2007
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    Confused Best air filter option for small return and limited furnace space.

    1st - Thanks everyone who contributes to these forums. They are a great source of info, and helped me choose a system.

    We hired a fully licensed HVAC contractor to put in a carrier infinity furnace, central air, and both EAC and media air filters (our family has bad allergies). Unfortunately, the estimator didn't measure everything out and there isn't room in the utility closet to add either of the Carrier brand filters. They did finish the job and put in what looked like a $0.50 green coarse-grain filter to protect the cooling coil in the near-term.

    My question is, what do you recommend we do? The options I can think of are:
    1. Only put in a 1" media filter in the furnace housing. This is pretty tricky as the Carrier Infinity furnace has electrical wiring blocking the right side entrance (so a disposable filter will not slide in), and also requires removing an interior access panel that is screwed in.
    2. Put in a media filter in the return air vent. Unfortunately, our return air grill is only 16 x 10 for a 1400 sq ft house. The furnace we have is 60k BTU matched with a 3T AC unit, and I'm concerned that a filter here might restrict the return air too much.

    I'm interested in having a licensed HVAC tech do this of course, but the comany we went with is being pretty flakey. I think if I do the deciding on what we want, they'll come and do it, but their estimator is pretty busy now that the warm season has started...

    Thanks for any thoughts...

  2. #2
    Join Date
    Jul 2006
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    The higher quality 1" pleated filters work well. You have to change them more often is all.

    The filter rack can be cut into and installed diagonally in the return duct if no room at the R/A furnace intake or at the RA grill. A diagonal install will allow more filter surface area.

    And your probably right the 10x16 is pretty small unless its a very short run

  3. #3
    Join Date
    Feb 2003
    Post Likes
    so, ask your contractor if a pleated filter will cause any problem!
    & how dense of a filter can be used!

    just because something can be done, does not mean that it should be -- learn the risks --
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  4. #4
    Join Date
    Aug 2002
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    16X10 return grille is likely too small for 3 Tons.Ask your installing contractor to show you how to read the Static(resistance ti air flow) on the Infinity Control,it may be too high to add a better filter.

    If it's too high the return and/or supply ducts may need ti be enlarged or ducts added.

  5. #5
    Join Date
    Jun 2005
    SW Wisconsin
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    Keep RA Velocities Low

    For a 3-Ton system @ 1200-cfm you need a 20" Return Air duct for 550-fpm airflow velocity.

    There is as lot to know concerning efficient duct system airflow performance.
    For a 3-Ton system @ 1200-cfm you should have a filter rack size of one, per two-cfm of airflow; or 600-sq.ins., for a 1200-cfm system.

    If the furnace filter rack is too small, you could use one or two external filter racks to achieve below 300-fpm airflow & a lower pressure drop through the filters.
    Click udarrell above, to access more info.
    Last edited by udarrell; 03-13-2009 at 08:49 AM. Reason: Removed inactive link

  6. #6
    Join Date
    Jan 2009
    Saint Joseph, MI
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    They make media filters in right angle housings. So it replaces the 90 degree transition on the return... so there's no additonal horizontal space needed.

    I agree with the others, a 3 tons of airflow needs at least a 16"x20" return. Ideally, you should try to fit a 20"x25" filter if possible.

    Take some pictures of the installtion and post them up here... maybe the pros can give some suggestions.

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