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Thread: High Low System

  1. #1
    I have a split level home built in 1988. On the second floor, I have floor vents and high/low vents in each room. Air is drawn in through the high/low vents and cold air/hot air comes out of the floor vents. My question? What do you call this system? Can I take a wall that has the high/low intake and "cap it" by taking off the top vent??? The intake on the bottom would remain. I would like to turn the wall into a waist high counter. Thanks for any help.

  2. #2
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    If it pulls air from below,which is likely as the supplies are in the floor,it's likely no problem to cap it off and just use the lower one.


  3. #3
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    Sounds like a high-low return system. The registers should have dampers in them. The idea is in the summer you open the top and close the bottom (pulls hot air from the ceiling. In the winter you should reverse this procedure and close the upper register and open the bottom (pulls cooler air from the floor in the return...
    I came into this world with nothing, I still have most of it left....

  4. #4
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    Usless 1950's invention.

    Provided the bottom return is enough by itself you should be ok.

  5. #5
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    Sorry,Doc, but it is very USEFULL.
    In the heating season take the return air from the floor level.
    In the cooling season take the return from near the ceiling .
    Normally, with this type of a high/low return system, the return space is in the SAME stud space. A damper is ONLY needed on the low grille. When the low grille damper is open, (heating season) this blocks off the high grille opening.
    When the low grille damper is shut,(cooling season) the high grille is open.

    Savvy?

  6. #6
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    Sorry "D" but the location of the return ,high or low, has little to no effect on comfort or preformance.

    The supplies however do ,as there is enough temperature difference and velocity to mix the air in the room properly.Returns don't have the effect.

  7. #7
    Thanks for info. It would seem that taking away the top intake vent would create little difference although there seems to be a difference of opinion about it.

  8. #8
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    Lets look at facts ,instead of opinions.

    Manual D ,the ANSI recognized authority,produced by the Air Conditioning Contractors of America,states the following;



    Section 1-4

    "Since the return location(high or low) has negligible effect on the air motion within the room(refer to ACCA's Manual T),the return openings should be placed at a positions that are compatable with the location of the equipment and the duct runs."



    Now to be fair,the idea of high and low returns is wide spread in the industry,it's just not true.

  9. #9
    Join Date
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    Originally posted by dash
    "Since the return location(high or low) has negligible effect on the air motion within the room(refer to ACCA's Manual T),the return openings should be placed at a positions that are compatable with the location of the equipment and the duct runs."
    That section in ACCA Manual T is 7-2.
    It states that a return grille having a high face velocity of 1000 FPM only has an effect of about 50 FPM about 15" in front of the grille.

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  10. #10
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    Thanks Dash, I agree, it really doesnt matter that much.

    IN the old days of gravity furnaces, it might have since there was a stratisifaction from high to low in the room. With todays systems on a properly designed distribution system, there is very little temperature difference from the floor to ceiling. We also desing systems to run, long off cycles may provide some temperature seperation but as soon as the fan comes on it pretty much goes by the way side.

    I used to have a buddy who insisted that you couldnt install a saddle valve for a humdifier on the top of the pipe becuase there was only water in the bottom of the pipe. He called himself a plumber.

  11. #11
    Join Date
    Feb 2005
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    344

    FUNNY

    Doc,

    That's funny. Years agoe I worked with a sheetmetal fabricator. One day he explained why duct takeoffs are never on the bottom of the trunk.

    "Everybody knows that pressure builds UP in the trnk. If the takeoff were on the bottom it would not get any flow."

    I have a lot of respect for this gentleman. I just let it go.

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