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  1. #1
    Join Date
    Apr 2004
    Posts
    7,680
    Ok... Here goes. I wanted to clear up this static regain once and for all for the Rheem/Ruud Air handlers.

    1st point.
    Per all brands residential air handlers installtion instructions. You should install the plenum the size of the opening. Yes this is true and this is the correct way.

    Point 2.
    May people dont follow point one. However, when the air handler is installed on a proper duct system it is irrelevent. If indeed the duct system is marginal (expecting a .5" ESP or more), then yes you can pick up around 100cfm by adding the static regain. If the duct system is crummy (expecting a ESP of .7" or more) then fix the duct issue. I have personally spent the day testing an air handler on various duct systems and until you reach .5" total static, the regain does nothing for you in the form of CFM. This is with a flow hood attached. At high static, its a moot point since you are starving the system anyway. Duct systems should be desinged to operate between .2" and .5" wc ESP. Follow manual D and you will not have a problem, do it with rules of thumb, and you get what you get, simply put.

    Point 3.
    Any air handler with electric heat strips should have 3' of non-combustable duct with no take offs. This is a safety thing should a heater disinigrate which is indeed the failure mode for electric heat. Horizontal and Downflow are obviously crucial since gravity is no longer a factor. See National Fire Protection Association 90A and 90B requirements.

    Point 4.
    ECM systems were not designed to overcome bad duct systems. They were desinged to maintain proper airflow in changing conditions at a more effeicient cost. Yes, a marginal duct system can be dealt with easily, a poor duct system may be dealt with but noise, and control become an issue. Even ECm's have a limit to RPMs and neat 1" they too will have to follow a curve.

    Point 5.
    The BHA air handler was a weaker motor and unless all was perfect they often had reduced airflow. That unit is no longer in production and has been replaced by the BHC in 2001 with a stronger motor. (900 RPM versus 825). The cabinet didnt change so neither did the thought process from the rumormill.

    Point 6.
    The flanges. The air handler is shipped with the duct flanges folded down for shipping and should be bent upright, even if the duct is not connected to them. Many mfg's do not have this but these do. The big orang label on the top of the unit clearly points out that these should be flipped up. Personal testing has shown anywhere from 10-25% airflow reduction if they are left down. Simply put, fold them up no matter where you attach the plenum.

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Thanks Doc.



    Re #2.
    I would have thought that the cfm gained ,would be a percentage of the total rather than ,around 100 cfm?

    I would have also thought that it would depend on the supply static ,more than the return.


    Re #4.

    Even though it was not the intended use,are you saying that ECM can overcome marginal to poor ,but not bad duct systems?

    That is what we have found,so far.

    [Edited by dash on 03-29-2005 at 12:39 PM]

  3. #3
    Join Date
    Apr 2004
    Posts
    7,680
    2. I tested a 4 ton ahu, it was 100 cfm, expect less on a smaller one.

    4. I am not suggesting ECM as a bandaid to the real problem but if you have marginal duct system, (.5 to .7) you might consider an ECM to get desired airflow, remember though, noise will become an issue and if too restrictive you will encounter huffing at the least. Yes, in many cases it will help but its not the solution. As an HVAC expert the duct system is part of the total system. It should always be evaluated when a new system is being installed otherwise its a glorified DIY project.


  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,803

    Wink

    Thanks doc, but you sound like you need a pint of chunky monkey.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Apr 2004
    Posts
    7,680
    Thanks, I'll stop and eat a pint today, might even get a pint of chubby hubby for the road.

    I apparently am not getting much argument so far, but Im betting it will be less than a week and we'll all see someone post "Does it have a static regain?" in reply to another post

  6. #6
    Join Date
    Oct 2004
    Posts
    3,400
    That would be me.
    I just like the way it sounds.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Doc,

    What about the cfm losses,when the ESP is say .5 on the supply side alone,for a total ESP of .6,as compared to .3 supply and .3 return?Would expect it to differ?

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by docholiday
    2. I tested a 4 ton ahu, it was 100 cfm, expect less on a smaller one.

    4. I am not suggesting ECM as a bandaid to the real problem but if you have marginal duct system, (.5 to .7) you might consider an ECM to get desired airflow, remember though, noise will become an issue and if too restrictive you will encounter huffing at the least. Yes, in many cases it will help but its not the solution.




    As an HVAC expert the duct system is part of the total system. It should always be evaluated when a new system is being installed otherwise its a glorified DIY project.

    If the last part is true,and I'm not saying it is not,the majority of systems installed in our area are "glorified DIY projects"!

  9. #9
    Join Date
    Apr 2004
    Posts
    7,680
    So be it... Hahah The ECM is an UPGRADE, not a BANDAID.

  10. #10
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    So many things I'd like to get off my chest about this POS air handler but everytime I start, I delete in fear of hurting feelings. I beg the OEM to bring back the *HQA. It worked so well for soooooo long.
    There is nothing more frightful than ignorance in action....Mark Twain

  11. #11
    Join Date
    Apr 2004
    Posts
    7,680
    So.... get em off yer chest.


  12. #12
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    Actually I have for the past several years. Feeling much better now.
    There is nothing more frightful than ignorance in action....Mark Twain

  13. #13
    Join Date
    Apr 2004
    Posts
    7,680
    Yeah, Ive read em, I was just hoping you had a legitimate one this time. Lol

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