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
    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
    9,937
    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

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event