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  1. #14
    Join Date
    Jul 2013
    Posts
    21
    Quote Originally Posted by udarrell View Post
    It is actually very simple;[B] I have tested it numerous times; reducing the negative pressure on the Return suction side increases the airflow to those rooms needing it on the Supply side...the blades of the blower wheel are not in any way starved of air to push into the Supply Air plenum; which also ultimately pushes more air back to the blower's intake; result a lot more airflow where you want it with the same air handler/blower
    I know you understood that...the rest depends on duct size, diffusers, possible 90 turning vanes, etc.

    It needs the bulk of the Return Air Area in the rooms where it needs the most airflow to & from those rooms & very little where there is plenty of airflow now.
    Unfortunately I don't have returns in the problem rooms, only a central return in the hallway. Maybe someday I will try to reroute the central return to the bedrooms

  2. #15
    Join Date
    Jul 2013
    Posts
    21
    I would also really appreciate final clarification if I can add more return air space in the basement to allow for a larger unit or if I should stick to 3T.
    We have a heatwave here this week and I really need to get a/c going

  3. #16
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,480
    Quote Originally Posted by fstr View Post
    I would also really appreciate final clarification if I can add more return air space in the basement to allow for a larger unit or if I should stick to 3T.
    We have a heatwave here this week and I really need to get a/c going
    You are not able to get enough A/C to the 2nd floor with the existing supplies, so a bigger system is only going to make matters much worse.

  4. #17
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,480
    Quote Originally Posted by fstr View Post
    Update on the returns: I figured based on previous comments that this is my limiting factor on system size and output so I opened all returns and did thorough investigation.
    First, as mentioned the main return at the AH is 12x20" So this is my max.
    The main return is divided in two (12x10" each). The one part of the return terminates on the 1st floor and the other on the second with openings of 9x8" and 13x8" respectively. Thus both registers are less than the duct they run through.
    The basement 6" return branches into the 8" return duct (so max between the 2 is 8", not 6" plus 8"). But better yet, the 8" duct splices into the return coming down from the 1st floor.

    Can someone please tell me the max cfm based on this info?

    I'm thinking I can ask when installing the new system to enlarge the return and add a dedicated return for the basement so that it does not tie into the 1st floor return. In addition I can enlarge the openings for the 1st and 2nd floor to 120sq inches each to maximize the use of the return ducts. Let me know if this is viable please.
    The 12"x10" duct is good for 600 CFM each. That will be limited or reduced by the return air grilles. Adding a large return to the basement, if open to the other levels, would help increase the return if needed.

    You're main problem is the lack of supply air to the 2nd floor. A 4 ton would be so wrong!

  5. #18
    Join Date
    Jul 2013
    Posts
    21
    Ok. Thanks for the responses. 3Ton it is. I think I will look into mini splits instead of upping the tonnage.
    Can someone please respond to my original question #3? I would like to know the size of the heatpack I should use.

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