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  1. #1
    Join Date
    Dec 2012
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    62

    4" Filter Confusion

    Filter Sizes

    I'm baffled by the range of choices for furnace filters.

    A new furnace that I'm having installed will have a custom built 20x20x4" media cabinet. But looking around, I'm seeing that the 4" filters are actually undercut to around 3 3/4"...which I assume will fit in my cabinet. To make matters even more confusing, there are some "so called" 4" filters that are really 4 3/16" to 4 3/8" that evidently are for the Honeywell cabinets. Not sure though. Where I'm really confused is that the 4" undercut filters seem to be pretty generic and not the best quality, again I think. Is the 3 3/4" size even standard so you can pick one up at a local store ?

    Merv Ratings

    I'd like a better Merv rated 4" filter....say around a Merv 10-13, but I'm worried about 2 things:

    1. Air resistance. Will it even work, or will it slowly destroy the furnace ?
    2. Is it realistic to change a Merv 10-13 filter every 6 months ?

    If not, then perhaps I should stick with the cheaper Merv 8's and change them more often ?

  2. #2
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    Is this media cabinet going on a furnace or a air handler? I've never measured the 4" filters at the Home Depot or Lowe's. It probably would be a good idea to make sure that the thicker filters (to give you more options). Or ask to have a larger cabinet installed. 3 3/4" sounds awfully narrow.

  3. #3
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    Dec 2012
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    Quote Originally Posted by George2 View Post
    Is this media cabinet going on a furnace or a air handler? I've never measured the 4" filters at the Home Depot or Lowe's. It probably would be a good idea to make sure that the thicker filters (to give you more options). Or ask to have a larger cabinet installed. 3 3/4" sounds awfully narrow.
    Furnace.

    Thanks George2 for the comments. The installer calls it a 4" media cabinet. It will take anything from a true 4" filter down to say a 1". Looking around I quickly noticed that most filters (except the Honeywell replacements) are actually undercut (like lumber) and their true dimensions are less. So for instance, a 4" will be around 3 3/4".

    4" filters do seem to readily available.......especially through HVAC companies and dealers, but the ones at HD's and Lowes...etc are usually the Honeywell replacements. Of course, there are a mega-zillion 1" 3M filters out there.

    I'm wondering more on what is the "sweet spot" for filter cost vs efficiency vs air flow in terms of Merv.
    Last edited by mixer440; 02-07-2013 at 10:52 PM. Reason: Added type of HVAC device

  4. #4
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,195
    Being a Trane XV95 DF system, I would want their Perfect Fit Media cabinet. The name alone explains why. The cabinet fits to the furnace like a hand fits a glove. It has gaskets that seal the door nicely. Very easy to open and close when replacing filters. Filters while proprietary size can be purchased at Internet filter houses, both OEM and generics.

    Without knowing more details about the reason for the custom cabinet, I think this is a stupid idea when Trane has a very nice, solid heavy duty cabinet that is made to fit their furnace. Therefore the name Perfect Fit media cabinet. BTW, the filters for the Trane cabinet are a nominal 5" depth.

    You are over thinking the MERV question. MERV 8-10 is the sweet spot
    for most homeowners and not restrictive.

    IMO

  5. #5
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    I agree with tigerdunes. The perfect fit while a little more $ compaired to say a air bear media filter and cabinet. The perfect fit is designed for Trane furnaces and air handlers to fit perfect under the unit. It is just like the clean effects makes for a clean install plus you get a 5" filter base.

    I would ask your installer to install a standard size 5" media filter like a 20x25 etc.. This will make it easy to get other types of aftermarket filters to fit into the cabinet if needed. While no need you can order from your dealer and in most cases have the next day. We stock common sizes at the shop for customers.

  6. #6
    Join Date
    Dec 2012
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    62
    Tiger and duck.....

    I'm sure the Trane unit is nice, but from what I see it is significantly more money. I'm going to look at the custom one and compare.


    I don't necessarily agree about the merv rating. There is a big difference between say an 8 and 11 or 13. But where I was concerned was air flow and how often you should really change a filter.
    Last edited by mixer440; 02-08-2013 at 11:57 AM. Reason: added merv comment

  7. #7
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    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    The reason I asked if it was going on a furnace is because you said they were offering a 20"x20"? I'm wondering why not a 20"x25"? Most standard furnace filters are 16"x25" which matches the furnace return opening.

    Also, the 20"x20" is an odd size which is harder to find, I would think.

  8. #8
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    Quote Originally Posted by mixer440 View Post
    Tiger and duck.....

    I'm sure the Trane unit is nice, but from what I see it is significantly more money. I'm going to look at the custom one and compare.


    I don't necessarily agree about the merv rating. There is a big difference between say an 8 and 11 or 13. But where I was concerned was air flow and how often you should really change a filter.
    Trane in no way is better then any other unit but you can't be just anyone to buy one like some other systems but that's another story all together.

    What furnace are you having installed? Does that manfactor not offer a common 4-5" filter enclosure? That is the reson we suggested the perfit fit it does just that makes for a perfit fit.

    Mev rating are important when it comes to air restriction. A merv 8-10 is all that I suggest as its a good mid ground that offers good filtration with taking away from the system when it gets a little dirty. Merv 11-13 real filtrate better but lead to decreased air flow once get a little dirty. Most customers don't change there filters as often as they should so it can lead to problems. I think you got the wrong idea we are not saying that merv 11-13 doesn't filtrate better because it does but can lead to what I talked about above. Common filter sizes are 16x25, 20x20, 20x25 in my area and are easy to find from OEM or aftermarket if you would prefer. Shoot its your system so put what you want in but we are just stated problems that we all see with high merv level filters.

  9. #9
    Join Date
    Dec 2012
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    62
    Quote Originally Posted by duckman06 View Post


    ............What furnace are u having installed? Does that manfactor offer a common 4-5" enclosure? That is the reason we suggested the perfit fit it does just that makes for a perfit fit.

    ........... Most customers don't change there filters as often as they should so it could lead to problems. ............. Shoot its your system so put what you want in but we are just stated problems that we all see with high merv level filters.
    Perfectly said duckman06, and don't get me wrong that's why I'm asking.
    The furnace is an XV 95 with an XLi 15 dual fuel

    The HVAC company installing the system has custom built air media cabinets with gaskets and will intergrste into most return configurations. Mine is a downflow, retrofit, and with tight space. The existing metal was 20x20, but only 1 inch.......so there are some limitations as to what might work. So, custom seems better.

    I will carefully consider your recommendations on filter efficiency.

    George2.......actually 20x20 is by far the most common sold size in my area.

    Everyone......What was confusing was that a 4 inch filter isn't really 4 inch and the Honeywell ones are over 4

  10. #10
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,013
    Quote Originally Posted by mixer440 View Post
    Filter Sizes

    I'm baffled by the range of choices for furnace filters.

    A new furnace that I'm having installed will have a custom built 20x20x4" media cabinet. But looking around, I'm seeing that the 4" filters are actually undercut to around 3 3/4"...which I assume will fit in my cabinet. To make matters even more confusing, there are some "so called" 4" filters that are really 4 3/16" to 4 3/8" that evidently are for the Honeywell cabinets. Not sure though. Where I'm really confused is that the 4" undercut filters seem to be pretty generic and not the best quality, again I think. Is the 3 3/4" size even standard so you can pick one up at a local store ?

    Merv Ratings

    I'd like a better Merv rated 4" filter....say around a Merv 10-13, but I'm worried about 2 things:

    1. Air resistance. Will it even work, or will it slowly destroy the furnace ?
    2. Is it realistic to change a Merv 10-13 filter every 6 months ?

    If not, then perhaps I should stick with the cheaper Merv 8's and change them more often ?
    The "average" filter will have dimensions a little smaller than the listed size. This probably is due to them wanting to make sure they fit into the vast majority of cabinets. The branded ones will be bigger because they are designed from the start as proprietary items that can only be purchased from specific outlets like the dealer that installed the filter rack/box.

    Air resistance can become an issue if the original install was not designed around the restrictiveness of the filter at the time to change it.
    When to change any filter is up to you and your home. The higher the Merv rating the more likely it is become full quicker because it is capable of stopping smaller particles. It all depends on what is floating around in the air in your home.
    If you want to know exactly when to change your filter you need to install a differential pressure gauge across the filter. When the pressure drop gets to the predetermined amount..... change the filter.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  11. #11
    Join Date
    Dec 2012
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    62
    Quote Originally Posted by firecontrol View Post
    The "average" filter will have dimensions a little smaller than the listed size. This probably is due to them wanting to make sure they fit into the vast majority of cabinets. The branded ones will be bigger because they are designed from the start as proprietary items that can only be purchased from specific outlets like the dealer that installed the filter rack/box.

    Air resistance can become an issue if the original install was not designed around the restrictiveness of the filter at the time to change it.
    When to change any filter is up to you and your home. The higher the Merv rating the more likely it is become full quicker because it is capable of stopping smaller particles. It all depends on what is floating around in the air in your home.
    If you want to know exactly when to change your filter you need to install a differential pressure gauge across the filter. When the pressure drop gets to the predetermined amount..... change the filter.
    Excellent information. I'm surprised that they don't have the air sensor/guage as an option and reported by the tstat. Seems like a good thing all away around. I'd rather have that, than some of the other bizarre marketing options they have on the top end ones.

  12. #12
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
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    Quote Originally Posted by mixer440 View Post
    Excellent information. I'm surprised that they don't have the air sensor/guage as an option and reported by the tstat. Seems like a good thing all away around. I'd rather have that, than some of the other bizarre marketing options they have on the top end ones.
    Some systems do measure pressure drop via feedback from the blower motor, but this is found on the highest end units. If you talk to your HVAC Co. I would guess they'd install a gauge for you.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  13. #13
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,695
    The counterflow furnace you have explains the 20"x20" filter a little better. Now I'm more concerned about the return air grille(s). I see a lot of home that are short on return with upflow furnaces and with counterflow furnaces almost always being short.

    Can you tell us how your return air is set up?

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