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Static pressure issue

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I have a 1500sqft house with a 3ton ML180uh070p36a-53 Lennox air handler. The static pressure according to the manual should be .5 max while heating, and .8 cooling.Pressure between the filter and the intake side of the fan while cooling is -.34, and +.58 between the fan and the cooling coil. I am over .12 static pressure. 

I can get the -.34 down a touch with a different filter maybe, but it's - .30 without a filter.  Can I add a vent in a room that is not part of the 1500SqFt that doesn't have ac and lower this pressure? If so, what size return & piping should I use ? 

TIA

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,635
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    I would check the static pressure on the discharge side of the coil before you do anything. If the coil is plugged or dirty adding ductwork will not help.
  • RPK
    RPK Member Posts: 109
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    Based on the measurements you gave your total external static pressure is 0.92”, checking static pressure downstream of the coil as EBEBRATT-Ed recommended is a good place to start. Do you know what fans speeds have been selected? The manual should have instructions and checking and adjusting airflow, that would also be good info to have before thinking about altering ductwork.
  • HVACNUT
    HVACNUT Member Posts: 5,865
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    What size furnace (not air handler) came out?
    If it has a 3 ton drive with a PSC motor, and all ductwork isn't sized properly, there will be issues. 
    What size is the air conditioning? 
    Upflow or horizontal mount?
    You could try lowering the blower speed on both cool and heat terminals on the circuit board, but make sure heat rise and sub cooling are still within specs.
    Intplm.
  • WildOates
    WildOates Member Posts: 5
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    Thanks for all the responces, I greatly appreciate the help.

    The unit is upright, and blows from bottom up.
    Not sure what the furnace is size is, I assume its design to do 2000sq ft as its packaged with the air handler. Part number is MX 600041-20, but I have not found the specs online yet. 

    I recheck measurements today. They are as follows. 

    On top of coil .46
    Between fan and coil .57
    Between filter and Fan .37


    The blower motor is set as follows.
    BLACK (High) Parked 
    BROWN (Med. High) wired to Heat
    YELLOW (Med Low) wired to Cool
    RED (Low)  Parked


    Thoughts?
    Park Yellow and try Red? 



  • pecmsg
    pecmsg Member Posts: 4,895
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    Your at .9

    what’s the temperature rise / drop
  • bburd
    bburd Member Posts: 924
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    Generally speaking, cooling requires a higher blower speed than heating.

    Bburd
  • WildOates
    WildOates Member Posts: 5
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    Hiw do I test for temperature rise and drop?
  • pecmsg
    pecmsg Member Posts: 4,895
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    air temperature in and out.

  • WildOates
    WildOates Member Posts: 5
    edited April 30
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    The air temp in was 71, the temp out was 50.

    What does this test help determine? Any next steps or thoughts on lowering the pressure?

  • WildOates
    WildOates Member Posts: 5
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  • GW
    GW Member Posts: 4,704
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    always confusion on this topic. Normally, the ratings are 'external to the unit', Not, external to the blower. That's a big difference, the coil gobbles up a bit.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • GW
    GW Member Posts: 4,704
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    your drop is 21 (dry bulb), which is good.

    But the real numbers need to include humidity numbers. I like to talk in 'wet bulb' numbers. If you can drop 10 deg wet bulb (Wb), that's very good. You can fiddle the fan speeds to see what speed is getting you the largest Wb drop, that's your sweet spot.

    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com