Page 3 of 3 FirstFirst 123
Results 27 to 30 of 30
  1. #27
    Join Date
    Mar 2008
    Location
    kansas
    Posts
    1,720
    Post Likes
    Quote Originally Posted by Leconte View Post
    Hold my beer.
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  2. #28
    Join Date
    Apr 2012
    Location
    Millsboro, DE
    Posts
    181
    Post Likes
    Good question, there's a lot of misinformation out there, even on very popular home TV shows with reputable HVAC "Experts".

    No residential return duct can be too big: The air will not "GET LOST IN THERE". If the duct is tight, the pressure difference will induce flow. Keep in mind the return duct is the most important duct in the home, because it is so often abused.

    Balancing a system before turnover is required by various ACCA Manuals and the IMC, maybe the IRC (don't know whether it contains "The Famous 16 Words" found in IMC 603.1). There are lots of things that can be done then to keep the flow within manufacturer's spec.

    I've rarely seen too much flow (ten times in 35 years???), and when I do it's because the startup person set the speed at the highest level before he walked out the door, not because of an oversized return.

    As for 0.10" friction, that started before AC became "necessary" for homes (40's? 50's?) and it always amazes to see guys who don't understand a blower will only do so much. .010" limits you to 300 to 400 feet of duct and fittings, quickly eaten up by high resistance duct fittings, improper flex workmanship, etc.
    Last edited by ferd1942; 02-21-2019 at 06:52 PM. Reason: clarify, expand

  3. #29
    Join Date
    Sep 2008
    Location
    VA
    Posts
    3,684
    Post Likes
    Over-sized return air is a myth. Unless you don't have any supply static. It is possible to over-amp a PSC blower motor with no static on it, but the evaporator itself puts enough static on it to drop it back down to FLA.
    Can you run too much air through a certain size coil, of course, but that has nothing to do with too large of a return, it has to do with too much blower. Most mfg's design their systems for a wide range of static pressures, 0"-.9"wc. Typically the 0" static on low speed will perform at 400cfm/ton +/-10%. If there is a concern for advanced humidity removal, then the contractor needs to design the system properly and look at the specs ahead of time. Variable speed motors work very well, and X13 motors usually allow for better low speed control.

    As for return air vents, they are only designed to depressurize a space, not to draw air in a particular pattern. Return air grilles can be over-sized if there are non-communicating spaces that utilize returns in those separated spaces.

    For instance:
    if you have space "A" supplying 750 cfm and space "B" supplying 250 cfm, you shouldn't install the larger return in space B.
    You run the risk of negatively pressurizing space "B" which can likely cause temperature imbalance.
    This is due to space "A" return air static being greater than space "B".
    With that said, if space "A" had a 0" static return it wouldn't much matter how large the space "B" return is, because you're only going to return what you supply.
    Last edited by mgenius33; 02-21-2019 at 08:53 PM.
    "The only true wisdom is in knowing you know nothing" Socrates

  4. #30
    Join Date
    Apr 2012
    Location
    Millsboro, DE
    Posts
    181
    Post Likes
    "Over-sized return air is a myth": Agreed MG!

    When we added cooling coils to the 0.10" FRICTION design in the 50's and 60's there began what I call a "War" between us (as I was then) contractors and equipment manufacturers: Contractors would kill a compressor due to low airflow (how many generations of heat pumps were there?) and manufacturers would retaliate by designing better compressors and air movers; the resulting escalation put us here with equipment only the best of you can properly install and/or troubleshoot.

Page 3 of 3 FirstFirst 123

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •