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  1. #1
    Join Date
    Mar 2009

    Default Heat/Air Problem

    Heat and air cond problems split slit level home
    (winter u-level get all the heat, summer l-level get all the air condition)
    The given is the my heating unit can only produces 100%
    Then if I set up the (5)braces at the plenum as follows:
    A) Only requires heat for 242 sq feet set the damper at 16%
    B) Only requires heat for 115 sq feet set the damper at 08%
    C) Only requires heat for 300 sq feet set the damper at 20%
    D) Only requires heat for 196 sq feet set the damper at 10%
    E) Only requires heat for 589 sq feet set the damper at 40%

    Question (2)
    Duct Booster fans
    Given my duct runs (might) be to long for the blower would you
    recommend the installing Duct Booster fans (at the registers)?

    Details of my home
    1. My home is (35 + years old), in Atlanta Georgia, facing west,
    2/4 framing, half brick half cedar siding
    2. I have a 4 bedroom split level home approx 1900 sq. feet with
    8 feet conventional ceilings
    2a. Overall upper level 38/24 feet 912 sq feet
    2b. Overall lower level 24/28 feet 672 sq feet
    2c. Lower level family room 26/12 312 sq feet
    2d. Overall House is 2,184,160 cu inches
    3. The lowest level (family room) is carpet over a slab of
    4. Windows as follows:
    4a. Upper level 10 single pane double hung with storms
    4b. Lower level 3 picture windows without storms
    4b1 5 double hung with storms
    4b2. One double pane slider
    5. I have added more insulation in the attic
    6. I had a problem with the original horizontal (gas) unit
    (parts were no longer available) so I was replaced the unit with
    a new vertical unit and had it installed in my (closed up,
    partially finished) garage.
    Note: when asked what size unit I wanted, I thought a new unit
    would be more efficient than my current unit. Thinking the cost
    of the new unit would reduce in my heating cost. I compares
    utility bills from the old and new, using only the BTU usage
    taking into consideration the HEAT DAYS published by NOAA, for
    three years. BOY WAS I WRONG
    6a. The new unit installed itís also (gas) same as original
    6b. The new unit is a Comfortmaker (Deluxe two stage gas
    furnace) with a AFUE of 80
    6c. The plenum has 5 branches as follows:
    A). 242 sq feet (u-level bedrm #1 and u-level small bath room)
    B). 115 sq feet (u-level bedrm #2)
    C). 300 sq feet (u-level bedrm #3 and l-level family room)
    D). 196 sq feet (u-level bedrm #4 and u-level hall bathrm
    E). 589 sq feet (l-level living, dinning and family rooms)
    6d. 464 sq feet for Miscellaneous halls, foyer, closets plus I
    eliminated a duct to the kitchen

  2. #2
    Join Date
    Aug 2007
    The Great White North

    Default Re: Heat/Air Problem

    While your proportional ratios may be logical unfortunately this may not be the case in practical terms. The issue has to do more with the required amount of cubic feet per minute air flow ( CFM ) needed to supply the size of the room. Also the amount of CFM of returm air flow to properly circulate the air maintaining a balanced flow.The size and distance the ducting is a big factor for proper flow.

    Unfortunately many times problems with air flow isn't as simple as playing with dampers. For example ... if a 5 inch duct has a capacity of 300 cfm and thinking that closing a damper somewhere downstream will increase the flow ..... well it can't provide any more than it can physically handle .... in other words if that duct is rated at 300 cfm max. you can't expect it to provide 400 cfm.

    If the lower level family room is lower than the level of the furnace .... that space will be cooler during the heating season. It's more difficult to move heated air downward since it wants to naturally rise. The opposite happens during the cooling season.... cold air wants to naturally settle downward so it's easier to move this air down.

    Personally I don't believe in using booster fans since this indicates a problem with the overall delivery system.
    There could be problems with improper duct sizes and/or length , leaks , too many restrictions , not enough or poor orientation of return air ducting , not enough CFM supply from the blower, etc..

    Sounds as though you would benifit having an HVAC contractor evaluate things first hand.

    Just a thought.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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