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  1. #1

    booster fans in 6" metal ducts

    Does anyone have any actual experience trying to increase air flow in a 6" hard metal duct using booster fans? My dining room gets air from a 25' long 6" duct, but it only as two bends, one at the start above the master duct and the other coming up through the wall. The actual gas blower is 4 tons and should be enough, but the force at the end is weak. Were you able to get a better air flow?

  2. #2
    Join Date
    Nov 2007
    Location
    Austin Texas
    Posts
    54
    Duct design is critically important - On your plenum (if a spider duct system) - is there a supply duct at the opposite end of the furnace output? By this I mean if there is a supply duct at the direct opposite end of the output of the furnace (whether it be a spider system or supply trunk line) - move it to the side of the ductwork and cap the end of the duct work. You could be losing a significant amount of static pressure that would be critical loss in the longer runs of a duct system (in a properly sized duct system). If you eliminate the obvious problems first, as a last resort, add the fan.
    Last edited by DavidInAustin; 12-02-2007 at 01:15 PM.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,189
    We've done it, to no success.

  4. #4
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    They don't work. Expierenced the same prob. Turned out I had a bryant frnace that could be equipped with a 1/4, 1/3, or a 1/2 horse power motor. Blower)

    I have 2500 sq ft and when I removed the the duct booster I happen to check my blower. It wa on a 1/3 so I bumped it too a 1/2. Got better airflow but still not as good as rest of house.

  5. #5
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    Quote Originally Posted by rkthomas13 View Post
    Does anyone have any actual experience trying to increase air flow in a 6" hard metal duct using booster fans? My dining room gets air from a 25' long 6" duct, but it only as two bends, one at the start above the master duct and the other coming up through the wall. The actual gas blower is 4 tons and should be enough, but the force at the end is weak. Were you able to get a better air flow?
    The propeller fans are nearly useless. The backward inclined booster fans work well.

    But it sounds like you have a bad duct design.

    If the ducts are accessible enlarging the trunk and branch duct will improve the air flow.
    Remember, Air Conditioning begins with AIR.

  6. #6
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,441
    I installed a propeller type booster fan in my house about 6 years ago and it worked great. this was for a small bathroom that had about 20 CFM coming out of the duct. fan boosted it to around 50. still awful, but the bathroom is plenty warm now. i think the duct separated in the wall, but there was no way to find or repair it.

    i don't know how much of a difference it would make to a room like your dining room that has a bigger load

  7. #7
    Join Date
    Apr 2004
    Posts
    7,680
    20-50 is certainly possible if the duct's problem was low supply static or the take off was in an eddy of sorts. Increasing one with a propellar type fan that actually blocks as much volume will hardly get you from say 70 cfm to 100.

  8. #8

    willing to look at my duct diagram and suggest?

    Would anyone be willing to look at a fax of the diagram of my ductwork and suggest where I might try to add booster fans, maybe spider cage fans or whatever to get more airflow on the other side of my house? I just can not find any hvac tech here who is willing to take on this kind of trial and error work. I can add the fans, but I need a pro to tell me what size and type to add and where.

  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Sure 352.795.6601

  10. #10

    diagram of ductwork

    Thanks. I shall post the diagram, (which I did myself, so not very pro), today. I also have digital pictures of the ductwork itself as well as the furnace, the steel supports, the joists, etc., which I could email to you so you have a better picture of my situation.
    I have tried to find a pro here with real experience of using dampers, booster fans, etc. to augment air flow and even out the heat, but so far have no really found anyone. I found plenty of guys who want to put in a new heat pump in the attic, but no one who has real experience making the existing system work better.

  11. #11
    Join Date
    Mar 2002
    Posts
    327
    If you call tech support for the blower manufacturer they will tell you where to put the fan for best performance. I did it and got 50% more air when I placed it where they suggested ( 2/3 of the way down the line) compared to where I placed it the first time (1/4 down the line).

  12. #12
    Join Date
    Dec 2006
    Posts
    82
    Make sure you get a real duct fan if you go that route. Here's two good ones:

    www.fantech.net/fkd.htm
    www.atmosphere.com

  13. #13
    Join Date
    Dec 2006
    Posts
    7
    If you ask your friends, neighbors, co-workers, etc... I'll guess that over 75% will note at least one room not having adequate airflow.

    Of the major home system areas (electrical, plumbing, framing, HVAC), I'll wager the HVAC sub-system is the LEAST professional and WORST implemented.

    Why? Most home owners know right away whether plumbing leaks, hot water is inadequate or fuses pop. However, it may take a homeowner years to "discover" poor HVAC performance - weather changes and demand of the HVAC system is hugely dependent on changing weather conditions.

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