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  1. #1

    Confused Blower fan speed?

    A tech recently serviced my Unitary/York heat pump/furnace and showed me an area inside the furnace where the blower speed could be changed. He suggested/changed the speed to High(from Low) and suggested I should change it to Medium in the winter. It may be obvious to some of you why this was suggested but its all Greek to me. Can someone help explain his recommendations?

    Thanks,

    George M!

  2. #2
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    Your blower speeds are set up to provide certain CFM'S depending on what type of system you have.

    I would think that a good tech would have set up all of the blower speeds for you and not told you what you may want to do. Did they check the static pressure after changing the speeds?

    This all needs to be set up by your contractor and if I were you I wouldn't mess with it.
    Its a good Life!

  3. #3
    Join Date
    Aug 2001
    Location
    forney texas
    Posts
    17,890
    with A/C you want to move aproximately 400 CFM(cubic feet minute) for proper cooling and Humidity removal. When the unit is switched to heat mode, you can have circumstances where the supply air might not go abouve 96 degrees. your body temp is 98.6 so 96 degree air will feel cold with a high CFM. slowing the air is more for comfort and a few degrees more heat, although 96 degree air will satisfy a t-stat set at 74-76.
    Last edited by acmanko; 08-01-2008 at 10:07 AM. Reason: spelling

  4. #4
    Join Date
    Aug 2003
    Posts
    466
    400 cfm of air per ton of cooling is the nominal amount of air that is usually preferred for general condtions. That 400 cfm per ton of air needs to be accurately measured in accordance to the static pressure of the air distribution system, which will be different for every duct system. For cooling in humid areas, less air is preferred to remove moisture from the air. This again needs to be properly calculated in order to not cause problems with the additional condensate on the coil freezing up.

    For the heat mode, the blower should be set to whatever speed keeps the temperature rise of the air across the heat exchanger closest to the mid-range of the temperature rise allowances that are listed on all furnace name plates.

    The bottom line is that you should never just change blower speeds without knowing what the quality of the air in the system is. This requires testing with air measuring devices such as anometers, manometers and magnehelic gauges. We wouldn't just take a guess at how much medicine we take, would we?

  5. #5
    Quote Originally Posted by everythingair View Post
    400 cfm of air per ton of cooling is the nominal amount of air that is usually preferred for general condtions. That 400 cfm per ton of air needs to be accurately measured in accordance to the static pressure of the air distribution system, which will be different for every duct system. For cooling in humid areas, less air is preferred to remove moisture from the air. This again needs to be properly calculated in order to not cause problems with the additional condensate on the coil freezing up.

    For the heat mode, the blower should be set to whatever speed keeps the temperature rise of the air across the heat exchanger closest to the mid-range of the temperature rise allowances that are listed on all furnace name plates.

    The bottom line is that you should never just change blower speeds without knowing what the quality of the air in the system is. This requires testing with air measuring devices such as anometers, manometers and magnehelic gauges. We wouldn't just take a guess at how much medicine we take, would we?
    Thanks .... Since I know nothing or next to it about this technolgy ... this is wonderful information and a great site.

    GM

  6. #6
    Quote Originally Posted by m kilgore View Post
    Your blower speeds are set up to provide certain CFM'S depending on what type of system you have.

    I would think that a good tech would have set up all of the blower speeds for you and not told you what you may want to do. Did they check the static pressure after changing the speeds?

    This all needs to be set up by your contractor and if I were you I wouldn't mess with it.
    If by contractor you mean the person that installed the system at this point I can't say that I trust the work that was done on the initial install 4.5 yrs ago. I have two systems and the system that servses the main floor and basement has never seemed to operate correctly. Without going into a lot of detail there seems to be an inordinate amount of time that the system calls for Aux Heat during the heating season. For example, when the outside temp is moderate (35-40), after the set point is reached, etc. The other system has no such issues. The tech in question (different company) was here looking at another issue with the heat pump itself when I mention this to him ... thats when he opened up the furnace/air handler to take a look see. He did not by any means suggest ths was my problem, which I think may be an inadequate system and/or a problem with the wiring. I have been through numerous service calls for this issue including changing out 2 Honeywell Chronotherm IV thermostats without any resolution. Any thoughts? Thermostat settings are @ 68 and I am located in Maryland.
    Last edited by GeorgeMJr; 08-01-2008 at 11:52 AM.

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