Results 1 to 6 of 6
  1. #1
    Join Date
    Jul 2010
    Posts
    25

    air filter inside the return

    Several years ago I had my HVAC system replaced and a contractor decided to make a custom (diagonal) opening in the return, right before it enters the system cabinet, so I can slide in air filters instead of changing them inside the unit.

    Is there a problem with air filter sitting inside the return or this is a common practice?

    Thanks

  2. #2
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    common practice, the diagonal cut is to give more surface area for the filter.
    Karst means cave. So, I search for caves.

  3. #3
    Join Date
    Feb 2001
    Posts
    35,838
    Be glad, thats how it should be instead of taking the furnace panel off.
    Used to be like all the time, back in the day.
    Hey cockroach, don't bug me! ©

    www.AskTheDiceman.com

    www.TheColdConspiracy.com

    www.Pennwood-HVAC.Com

    Bring Em Home....

  4. #4
    Join Date
    Jul 2010
    Posts
    25
    thanks for your quick responses

  5. #5
    Join Date
    Feb 2004
    Location
    Midwest
    Posts
    9,932
    If it's only one diagonal filter rather than a V configuration, you should have someone check the static pressure drop (resistance to airflow) across the filter. That diagonal scenario used by the old-timers LOOKS like it would work, but is actually extremely resistive to airflow. The bottom line is that the cross-sectional area of the duct still determines the filter resistance. I actually constructed some of these myself, and learned it the hard way on my own system.
    Let's say for example that you have a 12" high x 25" deep duct, and you put a 20" x 25" diagonal filter rack in it. You still have the SAME AIR VELOCITY moving through that 12" x 25" duct as you would have with a 12" x 25" vertical filter installed. And the velocity is what determines the pressure drop.
    That setup is fine as long as your system can get by with a filter that's the same dimensions as the return. But typically, this is not the case, because the filter needs a lot more cross-sectional area than the return.
    The only advantage to the diagonal filter is that it obviously has a higher dust holding capacity. But that's a moot point if it's WAY too restrictive when you put a brand new one in it, when it's undersized.

  6. #6
    Join Date
    Jul 2010
    Posts
    25
    will post a picture so you guys can criticize. It’s hard to explain using word

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image