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  1. #1
    Join Date
    Jun 2005
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    New England
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    906
    Hi - I have an evolution A/C system in my attic, with about 12 outlets. One 6" feed that goes all the way down to the basement, isn't really sufficient to cool it (we knew that when we put it in, but it was all there was room for). I don't mind most of the time, but when I have to work on hot weekend afternoons in the basement (that's where my 'office' is) it gets a bit hot. Yes, I know I could carefully adjust down the other 11 outlets to push more air into the basement, but I could also put a duct blower where the feed meets the main, put the power on a remote control, and just turn it on during those hot weekend afternoons. It probably won't increase airflow when the system is blowing high, but it will increase airflow when the system is on low. (my other option is a window air conditioner in my basement, but I don't think I really need it).

    My question: Since the variable speed fan adjusts for constant airflow, will an active cfm sink (like a blower on a feed) confuse the fan or otherwise mess things up.

    (and please don't say my contractor should come and balance the system - read my other thread (Did i buy the wrong furnace) to understand why he's not coming back 8-})

    Thanks!
    /j

  2. #2
    Join Date
    May 2006
    Location
    Las Vegas,Nevada
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    339
    Running a return to the basement would be a better solution. Is there one now? It sounds as though your basement is out of "the loop" with the rest of the house. Without proper airflow back out of the basement,you're pretty much forcing conditioned air in to a "can". Think of it as a regular space.Air flow in has to be equal to airflow out.

  3. #3
    Join Date
    Jun 2005
    Location
    New England
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    906
    actually, the door to the basement is almost always open, and there's a grille in the door for when it isn't. Also, unfortunately, there's no place to run a return back (other than maybe right next to the feed).

  4. #4
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,384
    Unless you installed a completely new duct system in your house you have a very unique situation as far as airflow goes.

    I have never needed to boost branch ducts with var spd blowers but I cannot think of any reason it would adversly affect the operation of the V/S blower. I suggest you contact Bryant support and ask them if they have an opinion.

    PS 48 pages and you don't update .

  5. #5
    Join Date
    Jun 2005
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    New England
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    nothing new to report there. Wheels are turning is all I can say. and don't get confused, my A/C duct system is both newer and way more normal than my heating duct system. But the run from the attic to the basement is a long one, and one 6" feed can't do more for a 24x24 room. But i was thinking with a booster it could do a bit more...

  6. #6
    Join Date
    May 2006
    Location
    Philadelphia, PA
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    1,384
    Ahhh. Seperate duct system. Why not try and balance it a bit. Close the ones closest to the air handler a little and see if it helps. Up to 1.0" static pressure the V/S blower will move the air it is set for. You might be surprised how much you can send to the basement without affecting the comfort of the rest of the house.

  7. #7
    Join Date
    May 2006
    Location
    Las Vegas,Nevada
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    I would try to slow down some or all of the other registers before going to the extreme of a duct booster fan.If the basement is open to the rest of the house,it will help to "balance" the system.Putting a booster on that leg may try to steal some of the air from other rooms where you may want/need it.I would spend a few days with the supply grill technique before going any farther.JMHO.If you can,decide which registers run from that trunk line and slow another branch down.As you close some registers, others will speed up and it will take some time to do but you can,with preserverance, get it to balance out.Just another brain fart, Was the basement included in the load calc. when the system was installed or was it an after thought? If it wasn't included, you may be looking at a window shacker as the only option.

    [Edited by smngmu on 08-05-2006 at 06:01 PM]

  8. #8
    Join Date
    Jun 2005
    Location
    New England
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    906
    Well, many of the ones closest are already closed down as far as I'd like to, and it's a hot, low-ceiling attic to have to crawl through to iteratively tweak them more. 8-}

  9. #9
    Join Date
    Jul 2006
    Location
    Lancaster,Ohio
    Posts
    464
    Sounds to me like a perfect situation for a mini split!
    IcyFlame

  10. #10
    Join Date
    Jun 2005
    Location
    New England
    Posts
    906
    hmmm $30 booster fan vs. $XXXX mini-split.... hmmmmmm
    8-}

    Actually, I was disappointed to see that, unlike the 8" duct fans I'm familiar with that boost 500cfm, the 6" at the Depot is rated at only 250cfm, - might not be much more than flows through the duct now - anyone know if I can get a 6" booster with, like 350-400cfm?
    ?j

  11. #11
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
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    3,304

    That could happen... not!

    I think you are being fooled by some unrealistic advertising on the box of the Home Depot product. 250 CFM? Is there any independent proof or reason to believe this will be true? Does it have the power to do that, and if so under what circumstances?

    When an AC system requires 1500 CFM airflow, would it be possible to buy 6 of these cheap fans and get the job done for a couple hundred dollars? I believe there is something about this cheap product which promises it won't succeed in that job.

    Note that a 6-inch duct has 28.3 sqin cross section area, or .20 sqft. If it WERE to blow air at 250 CFM it would be moving 1273 feet/min. This is a matter of simple mathematics and if I have not made an error it is unrealistic to expect any AC supply duct, flex or hard pipe, to carry this much air.

    To blow 400 cfm through a 6-inch pipe, would require 2037 feet/min. This is so far in violation of the Manual D speed limits that it's not even funny. Manual D specifies 700 max for flex duct and 1000 max for hard pipe. Go much beyond that and you will get a loud duct noise. No homeowner would want to build that into his system.

    The existence of the Home Depot fan may increase airflow a bit but I submit it will do far less than the box says, when you install it in your system. Personally I think the box is an example of more or less false advertising.

    If it were possible to replace that 6-inch duct with a larger one, that would be a professional and realistic way to increase your airflow. Can you do that in your system? Fantech makes some fans which can operate at high static pressures and may have the horsepower to move air much more than the Home Depot cheapies. But you are getting into some serious money with Fantech products.

    Hope this helps -- Pstu

    [Edited by pstu on 08-06-2006 at 08:38 PM]

  12. #12
    Join Date
    Jun 2005
    Location
    New England
    Posts
    906
    interesting point, and one that I'm in no position to refuse. Still - somethings' not right here....

  13. #13
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Try http://www.fantech.net

    these really work,and include the ESP ratings.


    When the booster fan comes on,the VS motor in the furnace will adjust,this will change the flow on the duct with the booster fan,then the furnacemay adjust again and again,in a never ending attept to "Set" the cfms thru the furnace.

    I really don't know for sure, how likely this is to happen,depends on how much the duct fan effects the flow, might be best to have the duct fan turned on before the furnace,and leave it on 24/7,to lessen the effect.

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